PULSE OXIMETRY

August 24th, 2015

PULSE OXIMETRY

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Prologue:

All of us know how important oxygen is for our survival. Hypoxia means low oxygen supply and/or utilization by organ or tissue. Hypoxemia means low oxygen content of arterial blood. Hypoxaemia invariably leads to hypoxia but hypoxia can occur even without hypoxaemia. Arterial blood oxygen saturation is now considered the 5th vital sign, joining: temperature, respiratory rate, heart rate and blood pressure. Hypoxemia can be present before recognizable signs of respiratory distress become evident and the traditional sign of circumoral cyanosis is a late indicator of decreased oxygenation. Blood gas analysis was for many years the only available method of detecting hypoxemia in critically ill patients, but this technique is painful, has potential complications, and does not provide immediate or continuous data. Pulse oximetry is an objective estimation of oxygenation, and it is simple, reliable, and accurate when used appropriately. It has the unique advantage of continuously monitoring the saturation of haemoglobin with oxygen, easily and noninvasively, providing a measure of cardio-respiratory function. Pulse oximetry is arguably the greatest advance in patient monitoring since electrocardiography. Hypoxaemia is commonly found in all aspects of medical practice and is a major cause of organ dysfunction and death. Since its introduction into clinical use in the 1980s, pulse oximeters have become ubiquitous clinical monitoring devices used throughout medical practice from operating theatres and intensive care units to outpatient departments and general practice clinics. However, clinically relevant principles and inherent limitations of pulse oximetry are not always well understood by health care professionals. Most of us have a thermometer, blood pressure cuff, or glucometer at home to track specific health concerns. We are just learning how helpful pulse oximeters are at home. The pulse oximeter is inexpensive and very easy to use as a trending tool for families at home.

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Abbreviation and synonyms:

O2 = Oxygen

CO2 = Carbon dioxide

CO = Carbon monoxide

PaO2 = partial pressure of oxygen in arterial blood expressed in mm Hg.

SaO2 = Oxygen saturation of hemoglobin in arterial blood measured by ABG/Co-oximetry expressed as percentage

SpO2 = Oxygen saturation of hemoglobin in arterial blood measured by a pulse oximeter expressed as percentage

CaO2 = Oxygen content of arterial blood in ml (dissolved oxygen plus oxygen bound to hemoglobin)

ABG = Arterial blood gases

EtCO2 = End-tidal carbon dioxide

SpHb = Hemoglobin estimated by non-invasive pulse co-oximeter

Oxyhemoglobin = Hemoglobin with attached oxygen

Deoxyhemoglobin = Hemoglobin without attached oxygen = Reduced hemoglobin

Functioning Haemoglobin = Hemoglobin which is capable of carrying oxygen. Functioning hemoglobin includes oxygenated hemoglobin (O2Hb) and deoxygenated hemoglobin (Hb).

Non-functioning Hemoglobin = Hemoglobin which is not capable of carrying oxygen. Non-functioning hemoglobin includes carboxyhemoglobin (COHb) and methemoglobin (MetHb).

Pulse oximetry  = Technique of measuring oxygen saturation of hemoglobin by shining red and infrared light through a peripheral site, such as a finger, toe, or nose.

Pulse oximeter = device that can detect a pulsatile signal in an extremity such as the finger or toe and can calculate the amount of oxygenated haemoglobin and the pulse rate.

Capnograph = monitor that detects the amount of carbon dioxide in each breath.

Hypoventilation = Breathing at a rate and/or depth that is less than normal.

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Note:

There is a confusing terminology in pulse oximetry. Everybody uses the term ‘oxygen saturation’ but it is not oxygen that is saturated with hemoglobin but hemoglobin is saturated with oxygen. 70 % oxygen saturation means 70 % of hemoglobin is saturated with oxygen (oxyhemoglobin) and remaining 30 % hemoglobin is without oxygen (deoxyhemoglobin). Hence the term ‘oxygen saturation of hemoglobin’ is more appropriate.

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Oxygen content in blood:

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Oxygen:

The fundamental purpose of the cardiorespiratory system is to deliver O2 and nutrients to cells and to remove CO2 and other metabolic products from them. Proper maintenance of this function depends not only on intact cardiovascular and respiratory systems but also on an adequate number of red blood cells and hemoglobin and a supply of inspired gas containing adequate O2. Body cells need oxygen to perform aerobic respiration. Respiration is one of the key ways a cell gains useful energy. The energy released in respiration is used to synthesize the adenosine triphosphate (ATP) to be stored. The energy stored in ATP can then be used to drive processes requiring energy, including biosynthesis, locomotion, or transportation of molecules across cell membranes. Decreased O2 availability to cells results in an inhibition of oxidative phosphorylation and increased anaerobic glycolysis. This switch from aerobic to anaerobic metabolism, the Pasteur effect, maintains some, albeit reduced ATP production. In severe hypoxia, when ATP production is inadequate to meet the energy requirements of ionic and osmotic equilibrium, cell membrane depolarization leads to uncontrolled Ca2+ influx and activation of Ca2+-dependent phospholipases and proteases. These events, in turn, cause cell swelling and, ultimately cell death. Human beings depend on oxygen for life. All organs require oxygen for metabolism but the brain and heart are particularly sensitive to a lack of oxygen. Shortage of oxygen in the body is called hypoxia. A serious shortage of oxygen for a few minutes is fatal.

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Survival time before cellular damage occurs after total loss of oxygen delivery (anoxia):

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Oxygen transport from air to tissues:

Oxygen in the atmosphere is brought into the lungs by breathing, and into the blood via lung capillaries. Then it is transported throughout the body by the blood. Each lung contains nearly 300 million alveoli which are surrounded by blood capillaries. Since alveolar walls and capillary walls are very thin, oxygen passing into the alveoli immediately transfers into the blood capillaries. (Usually in adults, the transfer would take about 0.25 seconds while resting.) A large proportion of the oxygen diffusing into the blood binds to hemoglobin in the red blood cells, while a part of the oxygen dissolves in the blood plasma. Blood enriched with oxygen (arterial blood) flows through pulmonary veins, then into the left atrium and left ventricle, and finally circulates throughout the body’s organs and their cells. The amount of oxygen transported around the body is determined mainly by the degree to which hemoglobin binds to oxygen (lung factor), hemoglobin concentration (anaemic factor), and cardiac output (cardiac factor). Oxygen saturation is an indicator of oxygen transport in the body, and indicates if sufficient oxygen is being supplied to the body.

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Oxygen transport:

Oxygen is inhaled into the lungs, and carbon (carbon dioxide) is exhaled from the lungs to the air. This process is called ventilation. Inhaled air flows into the upper airway, then into the peripheral airways, and is finally distributed into the lungs. This process is called distribution. The lungs consist of tissues called alveoli. Oxygen is absorbed from the alveoli, then into the lung capillaries via alveolar membranes, while carbon dioxide moves from the lung capillaries to the alveoli. This process is called diffusion.

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Oxygen is carried around the body attached to an iron-containing protein called haemoglobin (Hb) contained in red blood cells. After oxygen is breathed into the lungs, it combines with the haemoglobin in red blood cells as they pass through the pulmonary capillaries. The heart pumps blood continuously around the body to deliver oxygen to the tissues.

There are five important things that must happen in order to deliver enough oxygen to the tissues:

• Oxygen must be breathed in (or inspired) from the air into the lungs.

• Oxygen must pass from the air spaces in the lung (called the alveoli) to the blood. This is called alveolar gas exchange.

• The blood must contain enough haemoglobin to carry sufficient oxygen to the tissues.

• The heart must be able to pump enough blood to the tissues to meet the patient’s oxygen requirements.

• The volume of blood in the circulation must be adequate to ensure oxygenated blood is distributed to all the tissues.

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Function of Hemoglobin:

To support oxygen transport, hemoglobin must bind O2 efficiently at the partial pressure of oxygen (PO2) of the alveolus, retain it, and release it to tissues at the PO2 of tissue capillary beds. Oxygen acquisition and delivery over a relatively narrow range of oxygen tensions depend on a property inherent in the tetrameric arrangement of heme and globin subunits within the hemoglobin molecule called cooperativity or heme-heme interaction. At low oxygen tensions, the hemoglobin tetramer is fully deoxygenated. Oxygen binding begins slowly as O2 tension rises. However, as soon as some oxygen has been bound by the tetramer, an abrupt increase occurs in the oxygen binding. Thus, hemoglobin molecules that have bound some oxygen develop a higher oxygen affinity, greatly accelerating their ability to combine with more oxygen.

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Bound and dissolved oxygen:

Binding sites for oxygen are the heme groups, the Fe++-porphyrin portions of the hemoglobin molecule. There are four heme sites, and hence four oxygen binding sites per hemoglobin molecule. Heme sites occupied by oxygen molecules are said to be “saturated” with oxygen. The percentage of all the available heme binding sites saturated with oxygen is the hemoglobin oxygen saturation (in arterial blood, the SaO2).

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Since each hemoglobin molecule can bind to 4 molecules of oxygen, it may bind with 1 to 4 molecules of oxygen. However, hemoglobin is stable only when bound to 4 molecules of oxygen or when not bound to any oxygen. It is very unstable when bound to 1 to 3 molecules of oxygen. Therefore, as shown in the above figure, hemoglobin exists in the body in the form of deoxygenated hemoglobin (Hb) with no oxygen bound, or as oxygenated hemoglobin (O2Hb) with 4 molecules of oxygen. When all Hemoglobin molecules are bound with 4 molecules of oxygen, we call oxygen saturation 100 %. When 50 % hemoglobin molecules are bound with 4 molecules of oxygen, we call oxygen saturation 50 %. This oxygen saturation in percentage is measured by pulse oximetry.

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Hypoxia and hypoxaemia:

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Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during hypoventilation training or strenuous physical exercise. Hypoxia in which there is complete deprivation of oxygen supply is referred to as “anoxia”.  Hypoxia means low oxygen supply and/or utilization by organ or tissue. Hypoxemia means low oxygen content of arterial blood. Hypoxaemia invariably leads to hypoxia but hypoxia can occur even without hypoxaemia.  Ischemia, meaning insufficient blood flow to a tissue, can also result in hypoxia. This is called ‘ischemic hypoxia’. This can include an embolic event, a heart attack that decreases overall blood flow, or trauma to a tissue that results in damage. An example of insufficient blood flow causing local hypoxia is gangrene that occurs in diabetes. Diseases such as peripheral vascular disease can also result in local hypoxia.  Hypoxemic hypoxia (hypoxic hypoxia) refers specifically to hypoxic states where the oxygen content of arterial blood is insufficient due to poor oxygenation. This can be caused by alterations in respiratory drive, such as in respiratory alkalosis, physiological or pathological shunting of blood, diseases interfering in lung function resulting in a ventilation-perfusion mismatch, such as a pulmonary embolus, or alterations in the partial pressure of oxygen in the environment or lung alveoli, such as may occur at altitude or when diving. Hemoglobin plays a substantial role in carrying oxygen throughout the body, and when it is deficient, anemia can result, causing ‘anaemic hypoxia’. A chronic hypoxic state can result from a poorly compensated anaemia. Histotoxic hypoxia results when the quantity of oxygen reaching the cells is normal, but the cells are unable to use the oxygen effectively, due to disabled oxidative phosphorylation enzymes. This may occur in cyanide poisoning. An another instance of hypoxemic hypoxia would be when carbon monoxide is present in the blood, as hemoglobin has a higher affinity to carbon monoxide than oxygen. Not only does the carbon monoxide prevent the oxygen from reaching the cells, it is also a metabolic poison, compromising the cell’s ability to transport oxygen resulting in Histotoxic hypoxia. Pulse oximetry can measure hypoxemic hypoxia due to poor oxygenation by measuring oxygen saturation of hemoglobin but cannot measure anemic, circulatory, ischaemic or histotoxic hypoxia.

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If the O2 consumption of tissues is elevated without a corresponding increase in perfusion, tissue hypoxia ensues and the PO2 in venous blood declines. Ordinarily, the clinical picture of patients with hypoxia due to an elevated metabolic rate, as in fever or thyrotoxicosis, is quite different from that in other types of hypoxia: the skin is warm and flushed owing to increased cutaneous blood flow that dissipates the excessive heat produced, and cyanosis is usually absent.

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Carbon dioxide:

Carbon dioxide is produced by cell metabolism in the mitochondria. The amount produced depends on the rate of metabolism and the relative amounts of carbohydrate, fat and protein metabolized. The respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed while food is being metabolized.  RQ = CO2 eliminated/O2 consumed. The amount is about 200ml/min when at rest and eating a mixed diet; this utilises 80% of the oxygen consumed, giving a respiratory quotient of 0.8  A carbohydrate diet gives a RQ of 1 and a fat diet 0.7.

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Carbon dioxide transport in the blood:

There are 3 ways in which carbon dioxide is transported in the blood:

1. Dissolved CO2:

Carbon dioxide is 20 times more soluble than oxygen. About 5 % of carbon dioxide is transported unchanged, simply dissolved in the plasma. Arterial blood contains about 2.5 ml per 100 ml of dissolved carbon dioxide and venous blood 3 ml per 100 ml. A cardiac output of 5 liter per minute will carry 150 ml of dissolved carbon dioxide to the lung, of which 25 ml will be exhaled. Because of this high solubility and diffusing capacity, carbon dioxide partial pressure of alveolar and pulmonary end-capillary blood are virtually the same. Even a large shunt of 50% will only cause an end-pulmonary capillary/ arterial carbon dioxide gradient of about 0.4 kPa.

2. Bound to hemoglobin and plasma proteins:

Carbon dioxide combines reversibly with haemoglobin to form carbaminohaemoglobin. Carbon dioxide does not bind to iron, as oxygen does, but to amino groups on the polypeptide chains of haemoglobin. Carbon dioxide also binds to amino groups on the polypeptide chains of plasma proteins. About 10 % of carbon dioxide is transported bound to haemoglobin and plasma proteins

3. Bicarbonate ions (HCO3-):

The majority of carbon dioxide is transported in this way. Carbon dioxide enters red blood cells in the tissue capillaries where it combines with water to form carbonic acid (H2CO3). This reaction is catalysed by the enzyme carbonic anhydrase, which is found in the red blood cells. Carbonic acid then dissociates to form bicarbonate ions (HCO3-) and hydrogen ions (H+). This reaction also occurs outside the red blood cells, in the plasma, but is much slower due to the lack of carbonic anhydrase, so approximately 75% of carbon dioxide is transport in the red blood cell and 25% in the plasma. The hydrogen ions, formed from the dissociated carbonic acid, combine with the haemoglobin in the red blood cell.

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After releasing oxygen to the tissues, some of the Hb—which is now deoxygenated Hb—may pick up some of the carbon dioxide (CO2) formed as a by-product of cellular aerobic metabolism to form carbaminohemoglobin. Approximately 5%-10% of CO2 is transported as carbaminohemoglobin; the majority of CO2 (85% – 90%) is transported as bicarbonate. CO2 is transported to the lungs where it is released into the alveoli and eliminated in the process of ventilation.

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Measurement of oxygen:

Oxygen can be measured in three forms:

1. Partial pressure of oxygen (PO2)/partial pressure of arterial oxygen (PaO2)

2.  Oxygen saturation in arterial blood (SaO2) / Calculated estimate of oxygen saturation (SpO2) by pulse oximetry

3. Oxygen content in arterial blood (CaO2)

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Concept of partial pressure:

According to Dalton’s Law, the total pressure of a mixture of gases is the sum of the pressures of the individual gases.  In dry air, at an atmospheric pressure of 760 mm Hg, 78% of the total pressure is due to nitrogen molecules and 21% is due to oxygen. So atmospheric pressure of air is sum total of partial pressure of nitrogen and oxygen. Thus the PO2 that we breathe in is 160mm (760 X 0.21). After adjusting for dead airway space, elevation, patient temperature, and water vapor, the range of a normal PaO2 should be between 90-106 mm of Hg.

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The figure below shows fall in PO2 from 160 mm Hg in atmosphere to 100 mm Hg in alveoli and oxygenation of blood:

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PaO2 is partial pressure of oxygen in arterial blood. The arterial PO2 is frequently described as the PaO2 to denote that this is an arterial sample, as opposed to a venous or capillary PO2. PaO2, the partial pressure of oxygen in the plasma phase of arterial blood, is registered by an electrode that senses randomly-moving, dissolved oxygen molecules. The amount of dissolved oxygen in the plasma phase — and hence the PaO2 — is determined by alveolar PO2 and lung architecture only, and is unrelated to anything about hemoglobin. (With one exception: when there is both anemia and a sizable right to left shunt of blood through the lungs. In this situation a sufficient amount of blood with low venous O2 content can enter the arterial circulation and lead to a reduced PaO2. However, with a normal amount of shunting, anemia and hemoglobin variables do not affect PaO2.) Since PaO2 reflects only free oxygen molecules dissolved in plasma and not those bound to hemoglobin, PaO2 cannot tell us “how much” oxygen is in the blood; for that you need to know how much oxygen is also bound to hemoglobin, information given by the SaO2 and hemoglobin content. By administering supplemental oxygen or placing a patient in a hyperbaric chamber, PaO2 can be increased considerably resulting in increase of amount of oxygen that is dissolved in the arterial blood. The higher the partial pressure of oxygen, the more oxygen will be dissolved in blood. The normal partial pressure of oxygen in a human arterial blood is about 80-100 mm of mercury, and it refers only to the free oxygen within the blood, meaning the type that isn’t bound to hemoglobin.

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One of the main functions of blood is to receive oxygen from the lungs and transport it into the body’s tissues. At the same time, blood receives carbon dioxide from the tissues, and brings it back to the lungs. The amount of gas dissolved in a liquid (blood, in this case) is proportional to the pressure (partial pressure) of the gas. In addition, each gas has a different solubility. There are two mechanisms by which oxygen could be coalesced with blood. The first is when oxygen is dissolved in plasma due to the partial pressure difference of oxygen that is present in the surrounding atmosphere and the blood in the lungs. Partial pressure is the pressure exerted by a single component of a mixture of gases, commonly expressed in mm Hg; for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. This causes oxygen to dissolve in the plasma of the blood, for each 1mmHg partial pressure of oxygen 0.003ml dissolves in the plasma. Only about 0.3 ml of gaseous oxygen dissolves in 100 ml blood per mmHg (pressure). This amount is only 1/20 of carbon dioxide solubility. This suggests that a human could not get sufficient oxygen if solubility were the only way to get oxygen in the blood. For this reason, hemoglobin (Hb) has an important role as a carrier of oxygen. This is the second mechanism when oxygen binds with hemoglobin that is found in the red blood cells and forms oxyhemoglobin, which thereafter could be transported to all over the body, where the oxygen could be taken up, relieving the hemoglobin back to its original state. Here for every 1gm of hemoglobin, 1.34 ml of oxygen is carried. Since 100 ml of blood contain about 15 g of hemoglobin, the hemoglobin contained in 100 ml of blood can bind to 20.1 ml of oxygen. The dissolved fraction is available to tissues first and then, the fraction bound to hemoglobin. So as tissues metabolize oxygen or if oxygen becomes difficult to pick up through the lungs, the dissolved oxygen and the oxygen bound to hemoglobin will eventually become depleted. The dissolved oxygen can be measured by arterial blood gas analysis but this is not yet a practical field application. This fraction is not measured by pulse oximeter. The presence of available oxygen in form of oxyhaemoglobin in the blood could be simplified or rather related to what we call the oxygen saturation that is calculated by the pulse oximeter. The standard range for oxygen saturation is from 95-100% although a value up to 90% is accepted.

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The PO2 of RBCs is the same as the PO2 of the plasma, yet the oxygen content of the plasma is minute, compared to the oxygen content of RBCs because RBCs contains hemoglobin that binds a lot of oxygen while the plasma contains only minute amounts of dissolved oxygen.

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Correlation of partial pressure of oxygen and oxygen saturation of hemoglobin:

Oxygen molecules that pass through the thin alveolar-capillary membrane enter the plasma phase as dissolved (free) molecules; most of these molecules quickly enter the red blood cell and bind with hemoglobin. There is a dynamic equilibrium between the freely dissolved and the hemoglobin-bound oxygen molecules. However, the more dissolved molecules there are (i.e., the greater the PaO2) the more will bind to available hemoglobin; thus SaO2 always depends, to a large degree, on the concentration of dissolved oxygen molecules (i.e., on the PaO2). Because there is a virtually unlimited supply of oxygen molecules in the atmosphere, the dissolved O2 molecules that leave the plasma to bind with hemoglobin are quickly replaced by others; once bound, oxygen no longer exerts a gas pressure. Thus hemoglobin is like an efficient sponge that soaks up oxygen so more can enter the blood. Hemoglobin continues to soak up oxygen molecules until it becomes saturated with the maximum amount it can hold – an amount that is largely determined by the PaO2. Of course this whole process is near instantaneous and dynamic; at any given moment a given O2 molecule could be bound or dissolved. However, depending on the PaO2 and other factors, a certain percentage of all O2 molecules will be dissolved (about 1.5%) and a certain percentage will be bound (about 98.5%). PaO2 measures the oxygen that has passed through the lungs and into the blood. SaO2 measures the oxygen that has saturated the Hemoglobin in red blood cells after oxygen has passed into the blood from the lungs. In summary, PaO2 is determined by alveolar PO2 and the state of the alveolar-capillary interface, not by the amount of hemoglobin available to soak them up. PaO2, in turn, determines the oxygen saturation of hemoglobin (along with other factors that affect the position of the O2-dissociation curve, discussed below). The SaO2, plus the concentration of hemoglobin (15 gm/dl), determine the total amount of oxygen in the blood or CaO2 (vide infra). If the air is thin (at Mount Everest-low atmospheric pressure) or the lungs cannot take in oxygen appropriately due to any number of diseases, then obviously little oxygen gets into the lungs, into circulation, or both, thereby decreasing arterial partial pressure of oxygen. After oxygen has entered and dissolved within the blood, then, and only then, can oxygen bind to the hemoglobin in our blood. It is SaO2 that measures oxygen saturation of hemoglobin, and it should be clear that it depends on the partial pressure of arterial oxygen. If PaO2 drops, there’s less dissolved oxygen, and therefore less saturation of hemoglobin with oxygen. But oxygen saturation is tricky! If all of a sudden someone loses a lot of hemoglobin, as long as PaO2 remains the same, so will oxygen saturation. That’s because oxygen saturation measures the percentage of oxygen-binding sites occupied by oxygen on any and all remaining hemoglobin, not the total amount of oxygen bound to hemoglobin! Therefore both oxygen saturation and the partial pressure of oxygen in arterial blood are independent of the amount of hemoglobin in the blood. It is important to understand the difference between the PaO2, the oxygen saturation (SaO2), the oxygen content and the oxygen delivery rate.

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The PaO2 and the SaO2 are related to each other by the oxygen hemoglobin dissociation curve discussed vide infra. This curve plots the oxygen saturation (in %) on the vertical axis and PaO2 on the horizontal axis. The oxygen saturation % steadily increases as the PO2 increases up to about a PO2 of 100 mmHg at which point the oxygen saturation is 99% to 100% (i.e., all the hemoglobin oxygen binding sites contain oxygen). If the patient breathes supplemental oxygen, the inspired PO2 increases to 200 mmHg, 400 mmHg or higher depending on how much oxygen is inhaled. Thus, a patient breathing supplemental oxygen may have a PaO2 as high as 400 mmHg, but his oxygen saturation is still 100%, since it can’t get any higher than this. The higher PaO2 will increase dissolved oxygen in plasma but oxygen carried by hemoglobin will remain same.

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Oxygen saturation:

Red blood cells contain hemoglobin. One molecule of hemoglobin can carry up to four molecules of oxygen after which it is described as “saturated” with oxygen. If all the binding sites on the haemoglobin molecule are carrying oxygen, the haemoglobin is said to have a saturation of 100%. Oxygen is carried in the blood attached to haemoglobin molecules. Oxygen saturation is a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry. One haemoglobin molecule can carry a maximum of four molecules of oxygen. One hundred haemoglobin molecules could together carry a maximum of 400 (100 X 4) oxygen molecules, if these 100 haemoglobin molecules were carrying 380 oxygen molecules they would be carrying (380 / 400) X 100 = 95% of the maximum number of oxygen molecules that could carry and so together would be 95% saturated. Most of the haemoglobin in blood combines with oxygen as it passes through the lungs. A healthy individual with normal lungs, breathing air at sea level, will have an arterial oxygen saturation of 95% – 100% (PaO2 80 to 100mm). If the level is below 90 percent, it is considered low resulting in hypoxemia. Blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules (O2) enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation. Extremes of altitude will affect these numbers. Venous blood that is collected from the tissues contains less oxygen and normally has a saturation of around 75% (PaO2 40mm). Arterial blood looks bright red whilst venous blood looks dark red. The difference in colour is due to the difference in haemoglobin saturation.

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Oxygen saturation formula:

Oxygen saturation is a measurement of the percentage of oxygen binding sites that contain oxygen. If all the oxygen binding sites contain oxygen, then the oxygen saturation is 100%. Oxygen saturation is defined as the ratio of oxy-hemoglobin to the total concentration of hemoglobin present in the blood (i.e. Oxy-hemoglobin + reduced hemoglobin). When arterial oxy-hemoglobin saturation is measured by an arterial blood gas it is called SaO2. When arterial oxy-hemoglobin saturation is measured non-invasively by a finger pulse oximeter or handheld pulse oximeter, it is called SpO2. Note that SaO2/SpO2 alone doesn’t reveal how much oxygen is in the blood; for that we also need to know the hemoglobin content.

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However in practice there will always be some haemoglobin that is dysfunctional or combined with something other than oxygen and so is not available to carry oxygen.

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Functional oximetry vs. fractional oximetry:

It is important to understand the principle of the pulse oximeter so that a clinician has an understanding of what is actually being measured by the pulse oximeter and what its limitations are.  An understanding of fractional oximetry (SaO2) versus functional oximetry (SpO2) is necessary. Oximeters can measure either functional or fractional oxygen saturations. Functional saturation is the ratio of oxygenated haemoglobin to all haemoglobin capable of carrying oxygen; fractional saturation is the ratio of oxygenated haemoglobin to all haemoglobin (including that which does not carry oxygen). Fractional saturation is approximately 2% lower than functional saturation. SpO2 represents an estimate of functional arterial hemoglobin saturation, which refers only to the arterial hemoglobin that is capable of transporting oxygen (functional hemoglobin = oxyhemoglobin/ [oxyhemoglobin + deoxyhemoglobin]). Functional saturation differs from fractional hemoglobin saturation (Fractional hemoglobin = oxyhemoglobin/ total hemoglobin), which can be measured by most blood gas analyzers with co-oximetry. The total hemoglobin denominator in the calculation of fractional hemoglobin might include abnormal or variant hemoglobin molecules with limited oxygen-carrying properties. Therefore, the terms “functional” and “fractional” hemoglobin saturation are not interchangeable.  In situations such as dyshemoglobinemias, pulse-oximetry readings do not adequately reflect the oxygen-carrying properties of arterial blood.

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SaO2 is defined as the oxyhemoglobin (O2Hb) divided by the total hemoglobin (including all hemoglobin species) in a sample and can be written as:

SaO2 = O2Hb / [O2Hb + Hb + MetHb + COHb]

Where O2Hb is oxyhemoglobin, Hb is deoxyhemoglobin, Met Hb is methemoglobin, and COHb is carboxyhemoglobin.

You multiply above fraction by 100 to get SaO2 in percentage. These values are determined by analysis of arterial blood sample using co-oximetry.

SpO2 is defined as the oxyhemoglobin divided by all the functional hemoglobin in a sample and can be written as:

SpO2 = O2Hb/ [O2Hb + Hb] It is determined by pulse oximetry.

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The three most important measures of oxygen in blood are:

1. SaO2.  It’s a percentage that shows how saturated your arterial blood (hemoglobin) is with oxygen.  It’s obtained from an ABG with co-oximeter, so it’s very accurate.  Normal is 95-98%, although 90% or better is usually considered acceptable. It determines fractional oxygen saturation.

2. PaO2.  It’s the partial pressure of arterial oxygen.  It’s obtained from an ABG, and is an accurate measure of dissolved oxygen in arterial blood.  A normal range is 80-100 mm Hg, although 60 or better is usually considered acceptable.

3. SpO2. It’s similar to SaO2, although it’s estimated by pulse oximetry. A normal value is 95-98%, although 90% or better is usually considered acceptable. It determines functional oxygen saturation.

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Some important considerations:

1. CaO2 is arterial oxygen content. Unlike either PaO2 or SaO2, the value of CaO2 directly reflects the total number of oxygen molecules in arterial blood, both bound and unbound to hemoglobin. CaO2 depends on the hemoglobin content, SaO2, and the amount of dissolved oxygen. Units for CaO2 are ml oxygen/100 ml blood (see below).

2. PaO2 is a sensitive and non-specific indicator of the lungs’ ability to exchange gases with the atmosphere. In patients breathing ambient or “room” air (FIO2 = 0.21), a decreased PaO2 indicates impairment in the gas exchange properties of the lungs, usually signifying V-Q imbalance. PaO2 is a very sensitive indicator of gas exchange impairment; it can be reduced from virtually any parenchymal lung problem, including asthma, chronic obstructive pulmonary disease, and atelectasis that doesn’t show up on a chest x-ray.

3. FIO2 is the same at all altitudes. The percentage of individual gases in air (oxygen, nitrogen, etc.) doesn’t change with altitude, but the atmospheric (or barometric) pressure does. FIO2, the fraction of inspired oxygen in the air, is thus 21% (or 0.21) throughout the breathable atmosphere. PaO2 declines with altitude because the inspired oxygen pressure declines with altitude (inspired oxygen pressure is fraction of oxygen times the atmospheric pressure). Average barometric pressure at sea level is 760 mm Hg; it has been measured at 253 mm Hg on the top of Mt. Everest (8,848 metres above sea level). As one ascends rapidly to 3000 m (10,000 ft), the reduction of the O2 content of inspired air (FiO2) leads to a decrease in alveolar PO2 to approximately 60 mmHg, and a condition termed high-altitude illness develops. At higher altitudes, arterial saturation declines rapidly and symptoms become more serious; and at 5000 m, unacclimated individuals usually cease to be able to function normally owing to the changes in CNS functions.

4. Normal PaO2 decreases with age. A patient over age 70 may have a normal PaO2 around 70-80 mm Hg, at sea level. A useful rule of thumb is normal PaO2 at sea level (in mm Hg) = 100 minus the number of years over age 40.

5. The body does not store oxygen. If a patient needs supplemental oxygen it should be for a specific physiologic need, e.g., hypoxemia during sleep or exercise, or even continuously (24 hours a day) as in some patients with severe, chronic lung disease.

6. Supplemental O2 is an FIO2 > 21%. Supplemental oxygen means an FIO2 greater than the 21% oxygen in room (ambient) air. When you give supplemental oxygen you are raising the patient’s inhaled FIO2 to something over 21%; the highest FIO2 possible is 100%. To give more oxygen requires a hyperbaric chamber.

7. High FIO2 doesn’t affect COPD hypoxic drive. The reason a high FIO2 may raise PaCO2 in a patient with COPD is not because the extra oxygen cuts off the hypoxic drive. Modest rise in PaCO2 occurs mainly because the extra oxygen alters V/Q relationships within the lungs, creating more physiologic dead space.

8. A given liter flow rate of nasal O2 does not equal any specific FIO2. The often-quoted rule that 2 l/min = an FIO2 of 24%, 3 l/min = 28%, etc., is an illusion, based on nothing experimental or scientific. The actual FIO2 with nasal oxygen depends on the patient’s breathing rate and tidal volume, i.e., the amount of room air inhaled through the mouth and nose that mixes with the supplemental oxygen.

9. Face masks cannot deliver 100% oxygen unless there is a tight seal. So-called non-rebreather face masks can deliver an FIO2 up to around 80%. It is a mistake to label a patient with any loose-fitting face mask as receiving an “FIO2 of 100%.”  So100% oxygen can only be delivered with a ventilator or tight-fitting face mask.

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Oxygen content of arterial blood (CaO2):

Tissues need a requisite amount of O2 molecules for metabolism. Neither the PaO2 nor the SaO2 provide information on the number of oxygen molecules, i.e., of how much oxygen is in the blood. (Note that neither PaO2 nor SaO2 have units that denote any quantity.) Of the three values used for assessing blood oxygen levels, how much is provided only by the oxygen content, CaO2 (ml O2/dl). This is because CaO2 is the only value that incorporates the hemoglobin content.

Oxygen content can be measured directly or calculated by the oxygen content equation:

Oxygen content of blood = bound oxygen + dissolved oxygen

Bound oxygen = Hb in blood x 1.34 mlO2/ gm Hb x SaO2 in fraction (100% = 1)

Dissolved oxygen = PaO2 x 0.003mlO2/mmHg

In other words

CaO2 = [Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 fraction] + [PaO2 x (0.003 ml O2/mm Hg/dl)]

This calculation gives O2 in ml per 100 ml of blood. If the haemoglobin level is halved, the oxygen content of arterial blood will be halved.

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The oxygen carrying capacity of one gram of hemoglobin is 1.34 ml. With a hemoglobin content of 15 grams/dl blood and a normal hemoglobin oxygen saturation (SaO2) of 98%, arterial blood has a hemoglobin-bound oxygen content of 15 x .98 x 1.34 = 19.7 ml O2/dl blood. An additional small quantity of O2 is carried dissolved in plasma: 0.003 ml O2/dl plasma/mm Hg PaO2, or 0.3 ml O2/dl plasma when PaO2 is 100 mm Hg. Since normal CaO2 is 16-22 ml O2/dl blood, the amount contributed by dissolved (unbound) oxygen is very small, only about 1.4% to 1.9% of the total. Given normal pulmonary gas exchange (i.e., a normal respiratory system), factors that lower oxygen content – such as anemia, carbon monoxide poisoning, methemoglobinemia, shifts of the oxygen dissociation curve – do not affect PaO2. PaO2 is a measurement of pressure exerted by uncombined oxygen molecules dissolved in plasma; once oxygen molecules chemically bind to hemoglobin they no longer exert any pressure. PaO2 affects oxygen content by determining, along with other factors such as pH and temperature, the oxygen saturation of hemoglobin (SaO2). The familiar O2-dissociation curve can be plotted as SaO2 vs. PaO2 and as PaO2 vs. oxygen content. For the latter plot the hemoglobin concentration must be stipulated. When hemoglobin content is adequate, patients can have a reduced PaO2 (defect in gas transfer) and still have sufficient oxygen content for the tissues (e.g., hemoglobin 15 grams%, PaO2 55 mm Hg, SaO2 88%, CaO2 17.8 ml O2/dl blood). Conversely, patients can have a normal PaO2 and be profoundly hypoxemic by virtue of a reduced CaO2. This paradox – normal PaO2 and hypoxemia – generally occurs one of two ways: 1) anemia, or 2) altered affinity of hemoglobin for binding oxygen. A common misconception is that anemia affects PaO2 and/or SaO2; if the respiratory system is normal, anemia affects neither value. (In the presence of a right to left intrapulmonary shunt anemia can lower PaO2 by lowering the mixed venous oxygen content; when mixed venous blood shunted past the lungs mixes with oxygenated blood leaving the pulmonary capillaries, lowering the resulting PaO2) Obviously, however, the lower the hemoglobin content the lower the oxygen content. It is not unusual to see priority placed on improving a chronically hypoxemic patient’s low PaO2 when a blood transfusion would be far more beneficial. Anemia can also confound the clinical suspicion of hypoxemia since anemic patients do not generally manifest cyanosis even when PaO2 is very low. Cyanosis requires a minimum quantity of de-oxygenated hemoglobin to be manifest – approximately 5 grams% in the capillaries. A patient whose hemoglobin content is 15 grams% would not generate this much reduced hemoglobin in the capillaries until the SaO2 reached 78% (PaO2 44 mm Hg); when hemoglobin is 9 grams% the threshold SaO2 for cyanosis is lowered to 65% (PaO2 34 mm Hg). Altered hemoglobin affinity may occur from shifts of the oxygen dissociation curve (e.g., acidosis, hyperthermia), from alteration of the oxidation state of iron in the hemoglobin (methemoglobinemia), or from carbon monoxide poisoning. Carbon monoxide by itself does not affect PaO2 but only SaO2 and O2 content. To know the oxygen content one needs to know the hemoglobin content and the SaO2; both should be measured as part of each arterial blood gas test. A calculated SaO2 may be way off the mark and can be clinically misleading. This is true even without excess CO in the blood.

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How much oxygen in blood:

In a patient who is in good health:

• Each gram of haemoglobin combines with 1.34 ml of oxygen. Therefore, in blood with a normal haemoglobin concentration of 15g/dl, 100 ml of blood carries approximately 20 ml of oxygen combined with haemoglobin. In addition, a small quantity of oxygen is dissolved in the blood.

• The heart normally pumps approximately 5000 ml of blood per minute to the tissues in an average sized adult. This delivers about 1000 ml of oxygen to the tissues per minute.

• The cells in the tissues extract oxygen from the blood for metabolism, normally around 250ml of oxygen per minute. This means that if there is no oxygen being exchanged in the lung, there is only enough oxygen stored in the blood for around 3 minutes (only 75% of the oxygen carried by the haemoglobin is available to the tissues).

• Anaemic patients have lower levels of haemoglobin and are therefore unable to carry as much oxygen in the blood. At a haemoglobin concentration of less than 6g/dl, delivery of oxygen to the tissues may become too low to meet the metabolic demands. Patients who suffer major blood loss during surgery and become acutely anaemic should be given 100% oxygen to breathe. This will increase the amount of dissolved oxygen in the blood and will improve tissue oxygen delivery by a small amount. Blood transfusion may be life-saving.

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The oxygen content is determined by the oxygen saturation percentage and the hemoglobin concentration. A patient with hemoglobin of 14 has twice as much oxygen per ml of blood compared to a patient with a hemoglobin of 7, assuming that they both have 100% oxygen saturations. Similarly, the visual presence of cyanosis is dependent upon the concentration of desaturated (blue) hemoglobin. Thus, a patient with hemoglobin of 7 at 80% saturation has a deoxygenated hemoglobin concentration of 1.4. This patient will visually appear to be just as blue (though paler) as a patient with a hemoglobin of 14 at 90% saturation, since this latter person also has a deoxygenated hemoglobin concentration of 1.4. Additionally, a patient with hemoglobin of 14 at 80% saturation will look more cyanotic than a patient with a hemoglobin of 7 at 80% saturation. In this comparison, the more cyanotic patient is doing better with a higher oxygen content and oxygen delivery.

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The hematocrit is the percentage of the blood that contains RBCs. The hematocrit is directly proportional to the hemoglobin concentration. The hematocrit (in percent) is roughly three times the hemoglobin concentration (in gm per dl). Chronically hypoxic patients can survive by raising their hematocrit as a compensation maneuver. Chronic hypoxia stimulates erythropoietin which stimulates RBC production raising the hematocrit. Thus, a patient with a hemoglobin of 12 (hematocrit 36) and an oxygen saturation of 100%, has the same oxygen content as a patient with an oxygen saturation of 80% and a hemoglobin of 15 (hematocrit 45). The former patient looks pink, while the latter patient looks blue.

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Oxygen delivery:

The last factor is the oxygen delivery rate. This is determined by the oxygen content and the cardiac output. Conceptually, imagine a patient with a weak heart and only half the cardiac output of a normal patient with signs of congestive heart failure. If pulmonary edema were not present, and such a patient had an oxygen saturation of 100%, their hemoglobin would have to be twice as high as another patient with a normal cardiac output to achieve the same oxygen delivery rate. This might be better understood by measuring a patient’s venous blood gas. In room air, a normal arterial O2 saturation would be 100 %, and the venous O2 saturation would be about 75%. However, if a patient had a very low cardiac output, the arterial O2 saturation might still be 100%, but the venous O2 saturation might be 50%. This occurs because the cardiac output is so low, that much more oxygen is extracted from the RBCs as they pass through the capillaries. Mixed venous oxygen saturation (SvO2) is the percentage of oxygen bound to hemoglobin in blood returning to the right side of the heart.  This reflects the amount of oxygen “left over” after the tissues remove what they need. It is used to help us to recognize when a patient’s body is extracting more oxygen than normally. An increase in extraction is the body’s way to meet tissue oxygen needs when the amount of oxygen reaching the tissues is less than needed.

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Oxygen Haemoglobin dissociation curve:

The oxygen–hemoglobin dissociation curve plots the proportion of hemoglobin in its saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis. The oxyhemoglobin dissociation curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SaO2) and partial pressure of oxygen in the blood (PaO2), and is determined by what is called “Hemoglobin affinity for oxygen”; that is, how readily hemoglobin acquires and releases oxygen molecules into the fluid that surrounds it. The amount of oxygen dissolved in the blood is proportional to the partial pressure of oxygen. The amount of oxygen bound to hemoglobin will increase as the partial pressure of oxygen increases. But the amount of oxygen bound to hemoglobin does not increase in proportion to the partial pressure of oxygen. The increase may be indicated by an S-shaped curve as shown in the figure below. This is called the oxygen dissociation curve. The oxygen dissociation curve is called the “standard oxygen dissociation curve” in which the body temperature is 37°C, pH 7.4. The curve may shift to the right or left, depending on patient conditions. If the body temperature decreases and pH increases, the curve will shift to the left. If the temperature increases and pH decreases, the curve will shift to the right.

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At high partial pressures of oxygen, haemoglobin binds to oxygen to form oxyhaemoglobin.  When the blood is fully saturated, all the red blood cells are in the form of oxyhaemoglobin.  As the red blood cells travel to tissues deprived of oxygen the partial pressure of oxygen will decrease. Consequently, the oxyhaemoglobin releases the oxygen to form haemoglobin. The sigmoid shape of the oxygen dissociation curve is a result of the co-operative binding of oxygen to the four polypeptide chains. Co-operative binding is the characteristic of a haemoglobin to have a greater ability to bind oxygen after a subunit has bound oxygen. Thus, haemoglobin is most attracted to oxygen when three of the four polypeptide chains are bound to oxygen.

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The hemoglobin tetramer can bind up to four molecules of oxygen in the iron-containing sites of the heme molecules. As oxygen is bound, 2,3-BPG and CO2 are expelled. Salt bridges are broken, and each of the globin molecules changes its conformation to facilitate oxygen binding. Oxygen release to the tissues is the reverse process, salt bridges being formed and 2,3-BPG and CO2 bound. Deoxyhemoglobin does not bind oxygen efficiently until the cell returns to conditions of higher pH, the most important modulator of O2 affinity (Bohr effect). When a tissue is more active, the amount of carbon dioxide produced will be increased (PCO2 is higher). Carbon dioxide reacts with water as shown in the following equation:

CO2+ H2O <—->  H+ + HCO-3

What this means is that as the amount of carbon dioxide increases, more H+ are formed and the pH will decrease. Thus, a lower pH in the blood is suggestive of an increased carbon dioxide concentration which in turn is suggestive of a more active tissue that requires more oxygen. According to Bohr, the lower pH will cause Hb to deliver more oxygen! The high content of carbon dioxide in venous capillary blood reduces the affinity of haemoglobin for oxygen leading to release of oxygen to the tissues. The oxygen dissociation curve shifts to the right (Bohr effect).

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The partial pressure of oxygen dissolved in the plasma is measured as the PaO2. The oxygen dissociation curve shows the relation between SaO2 and PaO2. An SaO2 greater than 95% correlates to the normal range of PaO2, which is 80 to 100 mm Hg. A PaO2 of 60 mm Hg or less correlates to a SaO2 of less than 90% per the dissociation curve. Changes in temperature and pH cause a shift in this relation. As pH increases (alkalosis) or temperature decreases (hypothermia), the shift is to the left as hemoglobin binds more tightly with oxygen delaying its release to tissues. Acidosis (low pH) and fever shift the curve to the right, as the hemoglobin molecule loosens its affinity for oxygen, making it easier for oxygen to be released to the tissues.

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mm Hg O2 saturation
27 50 % This is the partial pressure of O2 with 50% saturation.
40 75 % This is the partial pressure of O2 in venous blood (PvO2).
60 90 %    Sats < 90% are entering the steep part of the curve.
100 98 % This is the partial pressure of O2 in arterial blood (PaO2).

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When oxygen saturation is measured in arterial blood (SpO2/SaO2):

97% saturation = 97 PaO2 (normal)

90% saturation = 60 PaO2 (danger)

80% saturation = 45 PaO2 (severe hypoxia)

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Clinical signs of hypoxemia:

Signs and symptoms of hypoxemia:

a. restlessness

b. altered or deteriorating mental status

c. increased pulse rate

d. increased or decreased respiratory rate

e. cyanosis (late sign)

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What is obvious breathing?

Normal breathing at rest is simply not obvious; one has to look very closely for chest movement to appreciate breathing. If a patient’s breathing is obvious on initial contact (for example, when you first see the patient on walking into the room) it is abnormal. Six signs that may make someone’s breathing obvious to the observer – all abnormal – are:

• flaring of nostrils with breathing

• tachypnea (generally, to be obvious, respiratory rate is > 24 breaths/min)

• noisy breathing (wheezing, stridor, moaning, etc.)

• use of accessory breathing muscles (neck muscles, intercostal muscles, etc.)

• pursed lip breathing (often seen in severe COPD)

• Cheyne-Stokes breathing (alternating periods of apnea with tachypnea; apnea periods may last up to 30 seconds)

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Fallibility of clinical signs of hypoxia:

Many studies have examined the use of simple clinical signs in assessing cardiopulmonary status in infants and children. In general these studies have shown that cardiorespiratory disease is frequently present when these signs are manifest, but of equal importance, the studies indicate the many children who have significant cardiorespiratory disease have none of these signs. Data from physiologic studies indicate that mild to moderate hypoxia produces at most a modest and temporary increase in ventilation. Transient hyperventilation is rapidly followed by a return to normal ventilatory levels. This biphasic response is a result of the way ventilation is controlled by the brainstem. Moderate hypoxia initially stimulates peripheral receptors to increase ventilation; however, the increase in ventilation produces a decrease in the PaCO2, an even more potent modulator of ventilation. In response to the decrease in the PaCO2, and because of a direct central depressive effect of hypoxia, the brainstem down-regulates the respiratory drive and returns ventilation back to baseline levels. Thus, most healthy individuals exposed to moderate hypoxia will not have a significant increase in their ventilation. Decreasing arterial oxygen pressure to less than 40 to 50 mm Hg produces a sustained increase in ventilation as the respiratory stimulation produced by hypoxia exceeds the inhibition generated by decreasing carbon dioxide levels.  It is important to note, however, that most of the initial increase in ventilation is accomplished by augmenting tidal volume and peak flows while keeping respiratory rate constant.  An increased respiratory rate occurs as a late response to severe hypoxemia. These physiologic findings suggest that in the clinical setting, respiratory rate should not be a sensitive indicator of arterial oxygen levels and cardiorespiratory status. One study confirms this concept. Only 48% of the children with SpO2 values of less than 90% had respiratory rate elevations above the 80th percentile for their age, and less than one third had rates in the upper 5th percentile for their age. The majority of the moderately hypoxic children in this study had respiratory rates that were indistinguishable from those of other children in the study. The fact that hypoxia may not be accompanied by an increased ventilatory drive may explain many of this study findings. In particular, this study demonstrates that after receiving triage pulse oximetry values, physicians were significantly more likely to change the treatment of children with SpO2 values of less than 95% compared with those having saturation values of 95% or greater. This is likely because of the difficulty physicians have in detecting cardiopulmonary and gas exchange abnormalities in patients who did not have evidence of respiratory distress. Without some sign of respiratory compromise, clinicians may often underestimate cardiorespiratory and gas exchange difficulties. Patients with pulmonary diseases such as viral respiratory tract infections, pneumonia, asthma, and bronchitis were most likely to have abnormal pulse oximetry values and were also most likely to have their medical treatment changed. This suggests that there were two reasons that pulse oximetry altered medical treatment: physicians either failed to appreciate subtle cardiopulmonary problems, or they did not recognize the severity of the illnesses they had diagnosed. Routine pulse oximetry measurements often alerted physicians to these problems by revealing SpO2 difficulties.

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Respiratory rate vs. SpO2:

Respiratory rate measurements are notoriously sensitive to measurement techniques and are often assessed inaccurately. Even if the respiratory rate is accurately measured, it is found that respiratory rates correlated poorly with SpO2 levels and that clinicians often changed their medical treatment after receiving pulse oximetry measurements. This confirms the findings of many investigators and demonstrates the inadequacy of the respiratory rate alone in screening for significant cardiopulmonary disease and gas exchange abnormalities.

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Hypoxemia is an important and potentially avoidable cause of morbidity and mortality in many hospital settings, including the intensive care unit (ICU), emergency department, procedure suite, and operating room. Rapid, accurate detection of hypoxemia is critical to prevent serious complications; however, oxygenation is difficult to assess on the basis of physical examination alone. The human eye is poor at detecting hypoxaemia. The traditional sign is cyanosis, which is defined as a concentration of more than 5 g/100 ml of reduced haemoglobin in capillary blood and depends on arterial oxygenation, skin perfusion, and haemoglobin content. The presence of central cyanosis, a blue coloration of the tongue and mucous membranes, is thought to be a more reliable indicator of hypoxaemia as these tissues are less likely to be poorly perfused. This definition translates to an oxyhaemoglobin saturation of about 75% with normal perfusion, which is clinically important hypoxaemia. The ability to detect cyanosis depends on the experience and eyesight of the observer, the colour balance of the ambient lighting, and the skin pigmentation of the subject. Places where hypoxaemia may be expected (operating theatres, accident departments, endoscopy suites) should have lighting with blue coloration (“northern daylight”) to facilitate detection. Several studies-the earliest was by Comroe and Bothelo in 1947 have shown that even under ideal conditions skilled observers cannot detect hypoxaemia until the oxyhaemoglobin saturation is under 80%. The pulse oximeter thus extends our clinical senses rather than replacing them. Because desaturation is detected earlier by pulse oximetry than by clinical observation, the use of pulse oximetry is recommended for any patient at risk for hypoxemia. Blood gas analysis was for many years the only available method of detecting hypoxemia in critically ill patients, but this technique is painful, has potential complications, and does not provide immediate or continuous data. Pulse oximetry allows noninvasive measurement of arterial hemoglobin saturation, without the risks associated with arterial puncture. Over the past 30 years, pulse oximetry has become the standard for continuous and/or noninvasive assessment of arterial oxygen saturation. Arterial oxygen saturation determination with pulse oximetry is now in such ubiquitous use that it has been called the “fifth vital sign”. Hypoxemia can be present before recognizable signs of respiratory distress-tachycardia, tachypnea, cyanosis, agitation, and lethargy-appear. But it wasn’t until the early 1980s that technology allowed for the easy and noninvasive measurement of arterial oxygen saturation. Initially used during surgery to prevent accidental death by oxygen desaturation, pulse oximeters are now found in nearly all settings, from EDs and ICUs to general units, and even in home care. The results of bedside pulse oximetry are at the heart of a wide range of clinical practice guidelines for patient care from the neonatal diagnosis of congenital heart disease to the management of chronic obstructive pulmonary disease and emergency oxygen therapy. Despite the widespread use of pulse oximetry in clinical monitoring, many practitioners are unaware of the potential limitations of this technology.

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The difficulty that physicians have in detecting hypoxemia was recently exemplified in a study of over 14000 patients being evaluated at the UCLA Emergency Department. Patients were monitored by oximetry but recordings were given to physicians only after they completed their initial assessment. Changes in diagnostic testing and treatment were most likely at an O2 saturation of 89%, and changes were actually less common at lower saturations, probably because the physicians were able to detect evidence of hypoxemia without requiring a pulse oximeter. With the proliferation of pulse oximeters in different locations of the hospital throughout the 1980s, several investigators demonstrated that episodic hypoxemia is much more common than previously suspected with an incidence ranging from 20–82%. The significance of episodic desaturation on patient outcome is largely unknown. In patients admitted to a general medical service, Bowton et al. found that O2 saturation <90% of at least 5 min duration occurred in 26% of the patients. On follow-up over the next 4–7 months, those patients experiencing hypoxemia during the first 24 h of hospitalization had more than a threefold higher mortality than patients who did not desaturate. Although episodic desaturation may simply be a marker of increased risk rather than the direct cause of decreased survival, an increased mortality rate was still observed in patients with episodic hypoxemia when the investigators corrected for severity of illness. Whether or not the early detection and treatment of episodic hypoxemia can affect patient outcome remains unknown.

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Methods for measuring oxygen saturation level:

Pulse Oximeter:

A pulse oximeter is a device intended for the non-invasive measurement of arterial blood oxygen saturation and pulse rate. Typically it uses two LEDs (light-emitting diodes) generating red and infrared lights through a translucent part of the body. Bone, tissue, pigmentation, and venous vessels normally absorb a constant amount of light over time. Oxy-hemoglobin and its deoxygenated form have significantly different absorption pattern. The arteriolar bed normally pulsates and absorbs variable amounts of light during systole and diastole, as blood volume increases and decreases. The ratio of light absorbed at systole and diastole is translated into an oxygen saturation measurement. Pulse oximeter is discussed in detail later on in the article. Pulse oximetry will not measure the oxygen saturation correctly for other hemoglobins such as methemoglobin or carboxyhemoglobin. However, for sickle hemoglobin or fetal hemoglobin, the measurement is nearly as accurate as for hemoglobin A.

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Co-oximeter:

Pulse oximeters estimate oxygen saturation by comparing the absorbance of light at two wavelengths. Infrared light is absorbed by oxyhemoglobin, whereas red light is absorbed by deoxyhemoglobin. The absorbance characteristics of methemoglobin are similar to those of oxyhemoglobin, falsely elevating pulse-oximeter readings. Co-oximeters measure light absorbance at four or more discrete wavelengths, providing accurate measurement of oxygen saturation, methemoglobin, and carboxyhemoglobin.  Co-oximeter is a device that measures the oxygen carrying state of hemoglobin in a blood specimen. Co-oximetry is useful in defining the causes for hypoxemia, hypoxia, or oxygen deficiency at the tissue level. The test is done with a device that measures absorption at several wavelengths to distinguish oxyhemoglobin from carboxyhemoglobin and determine the oxyhemoglobin saturation: the percentage of oxygenated hemoglobin compared to the total amount of hemoglobin, including carboxyhemoglobin (COHb), methemoglobin (metHb), oxyhemoglobin (O2Hb), and reduced hemoglobin (Hb). When a patient presents with carbon monoxide poisoning (CO), the Co-oximeter will detect the levels of each hemoglobin and will report the oxyhemoglobin saturation as markedly reduced. Traditionally, this measurement is made from arterial blood processed in a blood gas analyzer with a Co-oximeter.  More recently, pulse Co-oximeters have made it possible to estimate carboxyhemoglobin with non-invasive technology similar to a pulse oximeter [vide infra].  In contrast, the use of a standard pulse oximeter is not effective in the diagnosis of CO poisoning as patients suffering from carbon monoxide poisoning may have a normal oxygen saturation reading on a pulse oximeter.

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Oxygen saturation is measured by co-oximetry but this requires a blood sample.  Co-oximetry is capable of determining the true oxygen saturation for methemoglobin and carboxyhemoglobin. If the true oxygen saturation is known, then the PO2 can be estimated or calculated using the oxygen hemoglobin dissociation curve assuming that the patient is circulating hemoglobin A (which is not always the case).

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Arterial blood gas (ABG) analysis:

This is a blood test using samples extracted from an artery. The test determines the pH of the blood, the partial pressure of carbon dioxide and oxygen, and the bicarbonate level. Many blood gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxy-hemoglobin, carboxyhemoglobin and methemoglobin. The arterial blood gas analysis determines gas exchange levels in the blood related to lung function.

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An arterial blood gas (ABG) measures three components: pH, PCO2, PO2. All the other numbers on a blood gas are calculated. The bicarbonate (HCO3) value is calculated based on the measured pH and the measured PCO2, using the Henderson-Hasselbalch equation. The base excess (BE) is calculated using a similar equation. The oxygen saturation is calculated based on the assumption that normal adult hemoglobin (HbA) is the dominant hemoglobin in the sample (using the oxygen hemoglobin dissociation curve). How do venous and capillary blood gasses differ from an arterial blood gas? Looking at the three blood gas measurements: 1) The venous bicarb and the arterial bicarb are roughly the same. 2) The venous PCO2 is slightly higher than the arterial PCO2 because additional CO2 is picked up from the tissues, but the difference between the two is rather small. 3) The venous PO2 is substantially lower than the arterial PO2. Since only the PCO2 and the bicarb contribute to the pH, the venous pH and the arterial pH are roughly the same. A venous or a capillary blood gas very closely approximates the arterial pH, PCO2 and bicarb (or BE), under ideal conditions with well perfused tissues, but they do not approximate the arterial PO2. All that can be said about a venous PO2 is that it is lower than the arterial PO2. All that can be said about a capillary PO2 is that it lies somewhere between the venous PO2 and the arterial PO2. Fortunately, pulse oximetry accurately reflects the arterial PO2. Therefore, a venous blood gas or capillary blood gas done in conjunction with a pulse oximeter measurement, should accurately reflect the arterial blood gas as long as the capillary source is well perfused. Often, no blood gas is needed at all. The bicarb value can be obtained by ordering a standard set of electrolytes, the PO2 can be accurately estimated using a pulse oximeter, and the PCO2 can be clinically estimated using auscultation by listening for the degree of air exchange or by capnography.

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The means used to determine oxygen saturation vary. Oxygen saturation is a percentage value indicating the amount of hemoglobin that is saturated with oxygen.

There are three different ways to determine oxygen saturation.

They are the fractional oxygen saturation, the function oxygen saturation, and the calculated oxygen saturation measurements.

1. The first method of determining oxygen saturation is by measuring the O2Hb and comparing it to all the hemoglobin measured. This method is common for fractional oxygen saturation measurements (FO2Hb) from co-oximetry. The equation for which is: FO2Hb = [O2Hb /tHb] x 100

2. The second method of determining oxygen saturation is by measuring the O2Hb and comparing it to O2Hb + deoxyHb. This is referred to as functional hemoglobin saturation and can be determined by using co-oximetry as well as pulse oximetry. This allows clinicians to assess how much of the hemoglobin capable of carrying oxygen is actually saturated with oxygen molecules. The equation for this measurement is: SaO2= 100 X O2Hb / [O2Hb + deoxyHb].

3. The third method of determining oxygen saturations is by calculating the oxygen saturation (ScO2) using an equation or algorithm using a measured PO2, pH, PCO2, and a calculated/ default hemoglobin. The challenge with the calculated oxygen saturation is that clinicians must often assume normal hemoglobin values in their critically ill patients that receive a blood gas and that there are no other inhibitors such as MetHb or COHb.

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When comparing the above three different means of obtaining the oxygen saturation measurement, only O2Hb and SaO2 measured by co-oximeter provides direct measurement information to assess the oxygenation of hemoglobin. The use of ScO2 (calculated oxygen saturation) restricts’ the clinician’s ability to make a true determination of a patient’s oxygenation status by only assessing the oxygenation of the blood plasma and often assuming normal or default hemoglobin values in a patient. Therefore, in order to make an accurate assessment of a patient’s oxygenation statues, the PO2 measurement is needed in conjunction with the O2Hb measurement from a co-oximeter. Understanding the intent of an ABG is to measure both the acid-base balance and the oxygenation of a patient is fairly simple. However it is important for clinicians to understand the need to measure both the PO2 and O2Hb (by co-oximetry) in order to perform an accurate patient assessment of oxygenation. Once clinicians understand the need for co-oximetry with all ABG tests, the accuracy of a patient’s oxygenation will be assured.

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Other technologies that measure blood oxygen saturation:

Near-infrared spectroscopy (NIRS):

Near-infrared spectroscopy (NIRS) is a non-invasive technique for measuring blood oxygen saturation that may be more accurate and sensitive than pulse oximetry, especially in areas of prime interest such as cerebral tissue. NIRS is based on the light absorption characteristics of oxygenated and deoxygenated hemoglobin and provides a continuous measure of regional O2 saturation in a tissue field containing both venous and arterial blood. NIRS employs two photo-detectors adjacent to a single light source to measure light reflected by perfused tissue. The depth at which reflected light penetrates tissue is a function of the source-sensor distance that measures a shallow signal and a deep signal and subtracts commonalities without interference from the skin, skull, or subcutaneous tissue. The NIRS technique reduces placement constraints and affords greater subject mobility than finger-mounted pulse oximeters. The central position of NIRS sensors allows measurement of cerebral oxygenation, which is highly sensitive to acute changes in air oxygen content.  NIRS readings are independent of arterial pulse and in-house research has confirmed that NIRS is faster in reaching oxygen saturation benchmarks compared to a finger pulse oximeter. Although promising, research identified some drawbacks when using the NIRS (INVOS 5100C) sensor to detect varying levels of hypoxia exposure. Approximately 10% of subjects had baseline readings near or below the manufacturer recommended cut off (50%) for reliable readings. For subjects with low baselines, a large bias tended to exist between NIRS (normalized) and finger oximeter readings during minimum saturation plateaus, calling into question NIRS accuracy. The end result could be unacceptably high rates of false alarms for these individuals. Also, sensitivity to the placement of the sensors caused a fairly high degree of variation in daily baseline readings within individuals, such that baseline would likely need to be established prior to every flight. The baseline process takes approximately 10 minutes to complete which may be difficult to obtain during pre-flight procedures. Furthermore, similar to pulse oximetry NIRS is sensitive to G-induced drops in SPO2 which may make it difficult to determine whether a desaturation event is the product of stagnant or hypoxic hypoxia.

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NIRS tissue oxygenation compared to pulse oximetry in critically ill patients: 2007 study:

Tissue oxygen monitoring based on the principle of Near Infrared Spectroscopy (NIRS) is a more sensitive non-invasive measure of oxygenation compared to conventional pulse oximetry. In septic patients undergoing vasopressor therapy, continuous measurement of blood oxygenation by pulse oximetry becomes erroneous and unreliable. Tissue oxygen saturation measurement is a superior way to continuously monitor the patient’s clinical status and guide therapeutic decisions.

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Cerebral oximeter:

Cerebral oximetry is a non-invasive optical technology that measures cerebral cortex blood hemoglobin-oxygen saturation. Cerebral oximetry estimates the oxygenation of regional tissue by transcutaneous measurement of cerebral cortex using NIRS.

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Occlusion spectroscopy technology:

OrSense’s NBM200 is based on the company’s proprietary SpectOLight technology, which uses an optical measurement platform combined with a ring-shaped sensor that is fitted on the subject’s finger. A gentle pressure is applied by the sensor, temporarily occluding the blood flow in the finger. New blood dynamics are created, generating a unique, strong optical transmission signal, with a high signal-to-noise ratio which is wholly blood specific. During the occlusion, optical elements in the sensor perform a sensitive measurement of the light transmitted through the finger. This method, called Occlusion Spectroscopy, provides a quick, accurate and painless measurement of the subject’s blood constituents. The NBM 200MP system utilizes OrSense’s proprietary SpectOLightTM occlusion spectroscopy technology, a novel and improved method for measuring hemoglobin oxygen saturation. The system offers non-invasive, continuous and accurate measurement of oxygen saturation in states of hypovolemia, hypothermia and vasoconstriction, as well as during regular perfusion. In addition to oxygen saturation, the system provides Hemoglobin (Hb) values. The NBM 200MP’s superior performance was validated by multi-center trials in the United States and Europe.

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Vital signs:

Vital signs (often shortened to just vitals) are used to measure the body’s basic functions. These measurements are taken to help assess the general physical health of a person, give clues to possible diseases, and show progress toward recovery. The normal ranges for a person’s vital signs vary with age, weight, gender, and overall health. There are four primary vital signs: body temperature, blood pressure, pulse (heart rate), and breathing rate (respiratory rate). However, depending on the clinical setting these may include other measurements called the “fifth vital sign” or “sixth vital sign”. The fifth vital sign, pulse oximetry, routinely is used in every emergency department (ED) throughout the world. It is used to determine the baseline oxygenation of a patient in respiratory distress, to assess a patient’s response to therapeutic decisions, and to monitor a child during a conscious sedation or resuscitation. It is important to understand how the device functions and the limitations of this routinely used technology. Understanding that pulse oximetry measures functional saturation will help the clinician understand the limitations of this technology in the setting of a carbon monoxide exposure. It is also very important clinically to understand the limits of pulse oximetry in the setting of high venous pressures (congestive heart failure) or anemia. Certain clinical factors, such as sickle cell anemia, do not affect pulse oximetry, and the results provide meaningful information. As with every diagnostic test that a clinician performs, the information obtained is useful only if it can be interpreted accurately and applied appropriately to the individual patient.

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Pulse oximetry as a fifth paediatric vital sign: 1997 study:

The study included 2127 consecutive children presenting to triage at a university emergency department. Of 305 children having triage pulse oximetry values less than 95%, physicians ordered second oximetry for 49, additional chest radiography for 16, complete blood counts for 7, arterial blood gas measurements for 4, spirometry for 2, and ventilation-perfusion scans for 2. Physicians ordered 39 new therapies for 33 patients, including antibiotics for 15, supplemental oxygen for 11, and beta-agonists for 8. Five patients initially scheduled for hospital discharge were subsequently admitted. Physicians changed or added diagnoses in 25 patients. Using pulse oximetry as a routine fifth vital sign resulted in important changes in the treatment of a small proportion of paediatric patients.

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Pulse oximetry as a fifth vital sign in emergency geriatric assessment: a1998 study:

The study included 1,963 consecutive adults aged > or = 65 years presenting to triage at a university ED. 397 (20.2%) geriatric patients had triage pulse oximetry values <95%. Physicians ordered repeat oximetry for 51 patients, additional chest radiography for 23, CBC for 16, ABGs for 15, spirometry for 5, and ventilation-perfusion scans for none. Physicians ordered 49 new therapies for 44 patients, including antibiotics for 14, supplemental O2 for 29, and beta-agonists for 6. Nine patients initially scheduled for ED release were subsequently admitted to the hospital. Physicians changed or added diagnoses for 27 patients. Using pulse oximetry as a routine fifth vital sign resulted in important changes in the diagnoses and treatments of a small proportion of emergency geriatric patients.

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History of pulse oximetry:

Modern day pulse oximetry had its beginnings in avionics research. In the early days of high altitude flight, it was important to study the effects of cabin pressure on the oxygenation of blood in the circulatory system of pilots. In 1935, Karl Matthes, a German scientist, introduced the first ear oxygen saturation meter using 2 photo sensors and lights initially in the red and green wavelengths, subsequently changed to light in the red and infrared wavelengths. Several years later, a US scientist, Glenn Millikan, produced a lightweight portable ear oxygen meter for use in pilots. It was Millikan who coined the term oximeter to describe his device. The oximeter was first commercialized in the 1960s by Hewlett Packard (Palo Alto, California) who sold a $10,000 device for use in pulmonary and sleep laboratories. It was not until the early 1970s that 2 Japanese bioengineers, Takuo Aoyagi and Michio Kishi discovered that the transmission of the red and infrared frequencies of light through an earlobe showed variations corresponding with the pulsatile flow of arterial blood perfusing the tissue. They established that by measuring the pulsatile component of light transmission through living tissues they could eliminate the variable absorption of light by bone, skin, and venous circulation. They also discovered that the transmission of light in the red and infrared wavelengths could be used to calculate oxygen saturation in the arterial circulation of tissue being analyzed. The first pulse oximeters were manufactured in Japan in the late 1970s by Nihon Kohden and Minolta, but their clinical utility was unknown at the time. Following studies indicating that these devices could have widespread medical applications, pulse oximeters were commercialized in the United States in 1981 by Biox/Ohmeda (Ohmeda Medical; Boulder, Colorado) and by Nellcor (Covidien; Mansfield, Massachusetts) in 1983. The devices began to be used clinically, mostly by anaesthesiologists to monitor patients undergoing sedation and anesthesia. Over the next several years, accumulated data indicated that pulse oximeters could prevent 2000 to 10,000 anesthesia deaths each year from undetected hypoxemia. In 1986, the American Society of Anesthesiologists recommended that these devices be used to monitor patients undergoing anesthesia.  Over the next decade, pulse oximetry spread from the operating room to the emergency department, and then came to be used routinely in medical offices. Prior to the introduction of pulse oximetry, a patient’s oxygenation could only be determined by arterial blood gas, a single-point measurement that takes several minutes for sample collection and processing by a laboratory. In the absence of oxygenation, damage to the brain starts within 5 minutes with brain death ensuing within another 10–15 minutes. The worldwide market for pulse oximetry is over a billion dollars. With the introduction of pulse oximetry, a non-invasive, continuous measure of patient’s oxygenation was possible, revolutionizing the practice of anesthesia and greatly improving patient safety. By 1987, the standard of care for the administration of a general anesthetic in the U.S. included pulse oximetry. From the operating room, the use of pulse oximetry rapidly spread throughout the hospital, first to the recovery room, and then into the various intensive care units. Pulse oximetry was of particular value in the neonatal unit where the patients do not thrive with inadequate oxygenation, but too much oxygen and fluctuations in oxygen concentration can lead to vision impairment or blindness from retinopathy of prematurity (ROP). Furthermore, obtaining an arterial blood gas from a neonatal patient is painful to the patient and a major cause of neonatal anemia.  In 1995, Masimo introduced Signal Extraction Technology (SET) that could measure accurately during patient motion and low perfusion by separating the arterial signal from the venous and other signals. In 2011, an expert workgroup recommended newborn screening with pulse oximetry to increase the detection of critical congenital heart disease (CCHD). In 2011, the US Secretary of Health and Human Services added pulse oximetry to the recommended uniform screening panel. Before the evidence for screening using signal extraction technology, less than 1% of newborns in the United States were screened. Today, the Newborn Foundation has documented near universal screening in the United States and international screening is rapidly expanding.

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Principles of pulse oximetry:

Pulse oximetry uses light to work out oxygen saturation. Light is emitted from light sources which goes across the pulse oximeter probe and reaches the light detector. If a finger is placed in between the light source and the light detector, the light will now have to pass through the finger to reach the detector. Part of the light will be absorbed by the finger and the part not absorbed reaches the light detector. The amount of light that is absorbed by the finger depends on many physical properties and these properties are used by the pulse oximeter to calculate the oxygen saturation. Under normal physiological conditions arterial blood is 97% saturated, while venous blood is 75% saturated. The difference in absorption spectra of  O2Hb and deoxyHb is used for the measurement of arterial oxygen saturation because the wavelength range between 600 nm and 1000nm is also the range for which there is least attenuation of light by body tissues (tissue and pigmentation absorb blue, green and yellow light and water absorbs the longer infra-red wavelength).

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The principle of pulse oximetry is based on two technologies: infrared spectroscopy and pulse plethysmography.

1. Infrared spectroscopy detects the absorption of light by various tissues at two different wavelengths, namely the visual red and the infrared spectrum.

2. Pulse plethysmography describes the change in light absorption due to the pulsatile variation in volume of arteries and the transformation into a pulse waveform.

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The theory behind spectroscopy is described by the Beer-Lambert law, which states that the absorption of light by a tissue is proportional to the concentration of the tissue and the path length through that tissue. Therefore, the tissue to which the probe is applied has to be sufficiently thin and translucent. The diodes in the probe emit energy alternately at 660nm (visible red light spectrum) and 940nm (infrared light spectrum). The absorption of light at these wavelengths by Hb differs, depending on the degree of its oxygenation: reduced Hb absorbs more red light compared to oxyHb, which absorbs more infrared light. The photodetector measures the amount of light absorbed at each wavelength, from which the amount of oxyHb and deoxyHb is calculated by a microprocessor and displayed on the monitor.

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Modern pulse oximetry was born with the realization that pulsatile changes in light transmission through living tissues are due to alteration of the arterial blood volume in the tissue. Measurement of the pulsatile component would eliminate the variable absorption of light by bone, tissue, skin, pigment, etc from analysis. The most important premise of pulse oximetry therefore, is that the only pulsatile absorbance between the light source and the photo detector is that of arterial blood. Two wavelengths of light are used; 660 nanometers (red) and 940 nanometres (near infrared). At 660nm, reduced hemoglobin absorbs about ten times as much light as oxyhemoglobin. At the infrared wavelength, (940nm), the absorption coefficient of oxyhemoglobin is greater than that of reduced hemoglobin. The pulse oximeter directly senses the absorption of red and infra-red light, and the ratio of pulsatile to nonpulsatile light at the red and infrared wavelengths are translated through complex signal processing to a function of the arterial oxygen saturation. A microprocessor integrates the data, and through an elaborate calibration algorithm based on human volunteer data, the oxygen saturation can be estimated.

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Physics of pulse oximetry:

Pulse oximetry depends on spectral analysis for measurement of oxygen saturation; i.e. the detection and quantification of components in solution by their unique light absorption characteristics. The pulse oximeter combines the two technologies of spectrophotometry (which measures haemoglobin oxygen saturation) and optical plethysmography (which measures pulsatile changes in arterial blood volume at the sensor site). Detection of oxygen saturation of hemoglobin by spectrophotometry is based on Beer-Lambert law. This is a combination of two laws describing absorption of monochromatic light by a transparent substance through which it passes:

Beer’s law: the intensity of transmitted light decreases exponentially as the concentration of the substance increases. August Beer, German Physicist (1825-1863)

Lambert’s law: the intensity of transmitted light decreases exponentially as the distance travelled through the substance increases. Johann Lambert, German Physicist (1728-1777).

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Oxyhemoglobin absorbs more light in the infrared spectrum (850 to 1000 nm) whereas deoxyemoglobin absorbs more light in the red spectrum (600 to 750 nm). The pulse oximeter has two light emitting diodes (LED) of different wavelengths, one red and the other infrared. Typically the red LED has a wavelength of 660 nm and the infrared a wavelength of 940 nm. The LEDs are pulsed on and off hundreds of times per second and a photodetector collects the red and infrared light that passes through the tissue the pulse oximeter is placed on. A ratio of red to infrared light absorption is developed and applied to an internal algorithm in the pulse oximeters software. A number is then displayed on the readout. Newer pulse oximeters can compensate for extraneous light and the rapid sampling rate allows for detection of pulsatile blood flow which is assumed to be arterial. In clinical practice, a pulse oximeter is a non-invasive estimate of SpO2. This in turn can be used to estimate a patient PaO2 using the oxyhemoglobin dissociation curve.

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The light absorbed by non-pulsatile tissues is constant (DC). The non-constant absorption (AC) is the result of pulsatile blood pulsations. The photo detector generates a voltage proportional to the transmitted light. The AC component of the wave accounts for between 1-5% of the total signal. The high frequency of the diodes allows the absorption to be calculated many times per second. This reduces movement effects on the signal. The microprocessor analyses both the DC and AC components at 660 nm and 940 nm. The absorption of oxyhaemoglobin and deoxyhaemoglobin at these two wavelengths is very different. Hence, these two wavelengths provide good sensitivity.

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The figure above shows a schematic representation of the layers of human tissues that absorb light energy at the measuring site and the components of light absorption (constant—DC and variable—AC) by distinct tissue characteristics.  The pulse oximeter is able to differentiate between the absorption of light in the pulsatile (AC – alternating current) and the non-pulsatile (DC – direct current) flow under the probe. The AC component is derived from arterial blood pulsation, whereas the DC component is derived from all other static tissues, where the majority of total absorption occurs. The photodetector records the light transmitted through both pulsatile and non-pulsatile tissues. The AC component, the signal of interest, represents only up to two per cent of the total absorption (Magee, 2005). This explains how even small interferences, such as movement or vasoconstriction, may have a considerable impact on its accuracy. The difference in light absorption depends on variation in the amount of blood flowing underneath the probe, the erythrocyte concentration, local blood velocity and the distance between the light source and the detector.

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Isobestic point:

This is the point at which two substances absorb a certain wavelength of light to the same extent. In oximetry, the isobestic points of oxyhaemoglobin and deoxyhaemoglobin occur at 590 nm and 805 nm. These points may be used as reference points where light absorption is independent of the degree of saturation. Some earlier oximeters corrected for haemoglobin concentration using the wavelength at the isobestic points. Thus comparison of absorbencies at different wavelengths  allows estimation of the relative concentrations of O2Hb and deoxyHb (i.e. saturation). Modern pulse oximeters may use two or more wavelengths, not necessarily including an isobestic point.

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Currently available pulse oximeters are equipped with 2 light-emitting diodes (LEDs), 1 emitting at the red spectrum and the other at the infrared spectrum, most commonly at wavelengths of 660 and 940 nm, respectively. Emission of these 2 wavelengths alternates at frequencies of 0.6 to 1.0 kHz, and the nonabsorbed energy is detected by a semiconductor. A microprocessor subtracts the absorption by constant absorbers, thus rendering the final signal, which is displayed electronically as a plethysmographic wave form. The SpO2 is calculated from the conversion of the ratio of absorption ratios by using dedicated calibration algorithms stored in the microprocessor of the device. These algorithms are derived through SaO2 measurements in healthy volunteers breathing mixtures of decreased oxygen concentrations and are usually unique for each manufacturer.

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The pulse oximeter readings lag behind the patient’s condition because there is a response delay as a result of signal averaging in the monitor. The length of signal averaging can be set on some machines for 4, 8, or 16 seconds, with most oximeters having a common default setting of 8 seconds. This means there is an interval after the actual arterial blood oxygen saturation starts to fall before it is detected by oximetry because the signal is averaged over several seconds. The PaO2 could potentially decrease to a critical level before the decreased SpO2 is displayed by the oximeter. The clinician needs to be aware of this time delay between a potentially hypoxic event such as a respiratory obstruction and the pulse oximeter registering a low oxygen saturation.

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Calibration Adjustment:

Earlier I discussed how the pulse oximeter uses Beer’s and Lambert’s Law (absorbance depends on concentration and path length) as part of its factors that it uses to compute oxygen saturation. Unfortunately, there is a problem. In physics, the Beer and Lambert law have very strict criteria to be accurate. For an example, the light that goes through the sample should go straight through. However, in real life, this does not happen. Blood is not a neat red liquid. Instead, it is full of various irregular objects such as red cells etc. This makes the light scatter, instead of going in a straight line. Therefore Beer and Lamberts Law cannot be applied strictly. Because Beer and Lamberts law cannot be applied strictly, there would be errors if they were used to directly calculate oxygen saturation. A solution to this is to use a “calibration graph” to correct for errors. A test pulse oximeter is first calibrated using human volunteers. The test pulse oximeter is attached to the volunteer and then the volunteer is asked to breathe lower and lower oxygen concentrations. At intervals, arterial blood samples are taken. As the volunteers’ blood desaturates, direct measurements made on the arterial blood are compared simultaneously with the readings shown by the test pulse oximeter. In this way, the errors due to the inability of applying Beers and Lamberts law strictly are noted and a correction calibration graph is made. However, in order to not harm the volunteers, the oxygen saturation is not allowed to drop below about 75 – 80 %. A copy of this correction calibration graph is available inside the pulse oximeters in clinical use. When doing its calculations, the computer refers to the calibration graph and corrects the final reading displayed. As mentioned before, the volunteer studies described before do not allow the saturation to go below about 75 – 80 %. For saturations below this, the calibration curve is mathematically estimated .Therefore; pulse oximeters are typically less accurate below saturations of about 75 – 80 %.

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The pulse oximeter uses empirical calibration curves developed from studies of healthy volunteers to calculate SpO2. Pulse oximeters use two light emitting diodes (LEDs) of specific and differing wavelength (typically 660 and 940 nm) to measure the combined absorption by a mixture of oxyhaemoglobin and deoxyhaemoglobin of red and infrared light measured using a photodiode. The photodiode measures the variation in the intensity of light falling upon it, and converts this into an electrical voltage. The ratio of the absorption at these two wavelengths is called the R value, and is compared with R values that are calibrated against direct measurements of arterial oxyhaemoglobin saturation (SaO2) and arterial partial pressure of oxygen (PaO2) for an individual model of pulse oximeter, using a volunteer population sample. Volunteers breathe controlled hypoxic gas mixtures to create a range of SaO2 values between 70% and 100% against which the SPO2 of an individual pulse oximeter sensor may be calibrated. Pulse oximeters cannot determine the concentrations of oxyhemoglobin or deoxyhemoglobin; they provide an estimate of SaO2 rather than a direct measurement. For each of the two wavelengths of light used in pulse oximeters, a ratio of the relative absorbance of oxyhemoglobin and deoxyhemoglobin is calculated. This ratio is empirically related to SaO2, as measured in experimental studies in human volunteers. Since it is unethical to induce a degree of oxygen saturation below 70% in volunteers, pulse oximeter readings of approximately 70% represent the lowest limit of accurate output. It is recommended that readings lower than approximately 70% should be regarded as inaccurate since they represent extrapolation of the empirical data. Thus, pulse oximeters do not measure SaO2 but provide estimates. The accuracy of commercially available oximeters differs widely, probably due to the algorithm differences in signal processing.

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The pulse amplitudes (Vpp) of the red and infrared (IR) signals are measured and converted to Vrms, in order to produce a ratio value: Ratio = (Red_AC_Vrms/Red_DC) / (IR_AC_Vrms/IR_DC). The SpO2 can be determined using the ratio value and a look-up table that is made up of empirical formulas. The pulse rate can be calculated based on the pulse oximeter’s Analog-to-Digital Converter (ADC) sample number and sampling rate. A look-up table is an important part of a pulse oximeter. Look-up tables are specific to a particular oximeter design and are usually based on calibration curves derived from, among other things, a high number of measurements from subjects with various SpO2 levels. Figure below shows an example of a calibration curve.

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The performance of each device is strictly related to the reliability and complexity of the algorithms used in signal processing and to the speed and quality of the microprocessor. There are numerous studies of the accuracy and precision of pulse oximeters in various adult and paediatric populations. Most manufacturers claim mean differences (bias) of ≤2% with SDs (precision) of ≤4%.  It should be noted, however, that these results have been reported in subjects with SaO2 levels that exceed 80%; the performance of pulse oximeters deteriorates remarkably when SaO2 decreases to <80%.  95% confidence limit for Pulse Oximetry is +/- 4% at SpO2 >70% (the error is higher at SpO2 <70%). Correlation coefficients between pulse oximetry and direct blood oxygen saturation measurements are excellent, ranging from 0.77–0.99 when oxygen saturation is >70%.

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Accounting for ambient (room) light:

The pulse oximeter probe has a red LED and one infrared LED. On the other side, is a light detector. However, you will note that, though there are only two LEDs, the light detector is exposed to three sources of light. In addition to the red and infrared LED light sources, there is also light in the room (ambient light) that the pulse oximeter is working in. Some of this room light can also reach the detector. The pulse oximeter has to work with these three sources of light. It wants the red and infrared light to calculate oxygen saturation. On the other hand, the room light is unwanted “noise”, and needs to be taken account of. In reality, both LEDs are never lit together. Instead, the pulse oximeter rapidly switches the LED’s on and off in a particular sequence. First, the pulse oximeter activates the red LED light. The red light goes through the finger and reaches the detector. Stray room light also reaches the detector. The detector therefore records red light and room light that falls on it. Next, the pulse oximeter switches off the red LED light and switches on the infrared LED light. The infrared light goes through the finger and reaches the detector. Stray room light also reaches the detector. The detector therefore records infrared light and room light that falls on it. Finally the pulse oximeter switches off both the red and infrared LED lights. Now the only light that falls on the detector is the room light. The pulse oximeter now records the room light level. Because the pulse oximeter now knows the level of room light, it is able to subtract it from the readings to get the actual red and infrared light levels.

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Pulse plethysmography:

Plethysmographic trace (Pleth):

Pulse oximeters often show the pulsatile change in absorbance in a graphical form. This is called the “plethysmographic trace ” or more conveniently, as “pleth”. The pleth is an extremely important graph to see. It tells you how good the pulsatile signal is. If the quality of the pulsatile signal is poor, then the calculation of the oxygen saturation may be wrong. The pulse oximeter uses very complicated calculations to work out oxygen saturation. A poor pleth tracing can easily fool the computer into wrongly calculating the oxygen saturation. As human beings, we like to believe what is good, so when we see a nice saturation like 99 %, we tend to believe it, when actually the patient’s actual saturation may be much lower. So always look at pleth first, before looking at oxygen saturation. The pleth is affected by factors that affect the peripheral blood flow. For an example, low blood pressure or peripheral cold temperature can reduce it. Sophisticated uses of the pleth are being developed. For example, it may be used to guide fluid therapy. Most pulse oximeters display oxygen saturation, heart rate and a plethysmographic trace. The most important function of the plethysmogram is to provide information regarding whether the pulse oximeter is working correctly. Readings displayed are only accurate and, therefore, reliable if this trace resembles an arterial pressure waveform and if the pulse rate displayed equals the actual patient’s pulse rate. The plethysmogram is also useful as an indicator of cardiac rhythm, as arrhythmias may result in changes in its regularity. Changes in cardiac output may be assessed by a change in amplitude of the trace and the area under the curve.

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When properly attached, the ideal plethysmograph waveform shows a dicrotic notch as shown in the figure below:

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Pulse oximetry signals:

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A number of physiologic variables affect SpO2 reading:

1. Arterial blood flow to the vascular bed

2. Temperature of the digit or the area where the oximetry sensor is located

3. Patient’s oxygenation ability

4. Percentage of inspired oxygen

5. Ventilation-perfusion mismatch

6. Amount of ambient light seen by the sensor

7. Venous return at the probe location

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Procedure of pulse oximetry:

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Pulse oximetry is a simple non-invasive method of monitoring the percentage of haemoglobin (Hb) which is saturated with oxygen. The pulse oximeter consists of a probe attached to the patient’s finger or ear lobe which is linked to a computerised unit. The unit displays the percentage of Hb saturated with oxygen together with an audible signal for each pulse beat, a calculated heart rate and in some models, a graphical display of the blood flow past the probe. Audible alarms which can be programmed by the user are provided. An oximeter detects hypoxia before the patient becomes clinically cyanosed. A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient’s blood (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin, producing a photoplethysmogram. The pulse oximeter may be incorporated into a multiparameter patient monitor. Most monitors also display the pulse rate. Portable, battery-operated pulse oximeters are also available for transport or home blood-oxygen monitoring. Continuous monitoring of arterial blood gases requires either repeated arterial punctures or an indwelling arterial catheter, and so may be difficult in many circumstances. Instead, the oxygen saturation fraction of hemoglobin can be measured continuously using pulse oximetry. However, since oxygen content varies relatively little with PaO2 at saturations above 90%, it is difficult to know the precise PaO2 using this device. In addition, PaCO2 is needed to fully assess the mechanism of hypoxemia, a value that is not revealed by pulse oximetry.

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The body’s need for oxygen is certain. Its availability at a tissue level is sometimes in doubt. Blood gas measurements provide critical information regarding oxygenation, ventilation, and acid-base status. However, these measurements only provide a snapshot of the patient’s condition taken at the time that the blood sample was drawn. It is well known that oxygenation can change very quickly. In the absence of continuous oxygenation monitoring, these changes may go undetected until it is too late. Pulse oximeters measure blood oxygen saturation noninvasively and continuously. Pulse oximeters are used widely in emergency departments, anaesthesiology, and critical care. However, data on the role of pulse oximeters in general practice is limited. A recent survey of GPs revealed a minority (9%) reported they used a pulse oximeter to measure pulse rate, or to assess respiratory status (20%). In clinical examination, a traditional sign of hypoxia is central cyanosis. However, studies have shown clinicians have difficulty in reliably detecting hypoxaemia until the saturation is <80%.

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Pulse oximeters may be used in a variety of situations but are of particular value for monitoring oxygenation and pulse rates throughout anaesthesia. They are also widely used during the recovery phase. The oxygen saturation should always be above 95%. In patients with long standing respiratory disease or those with cyanotic congenital heart disease readings may be lower and reflect the severity of the underlying disease. In intensive care oximeters are used extensively during mechanical ventilation and frequently detect problems with oxygenation before they are noticed clinically. They are used as a guide for weaning from ventilation and also to help assess whether a patient’s oxygen therapy is adequate. In some hospitals oximeters are used on the wards and in casualty departments. When patients are sedated for procedures such as endoscopy, oximetry has been shown to increase safety by alerting the staff to unexpected hypoxia.

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Pulse oximetry provides a simple, non-invasive approximation of arterial oxygenation in a wide variety of clinical settings including emergency and critical-care medicine, hospital-based and ambulatory care, perioperative monitoring, inpatient and outpatient settings, and for specific diagnostic applications. Pulse oximetry is of utility in perinatal, paediatric, adult and geriatric populations but may require use of age-specific sensors in these groups. It plays a role in the monitoring and treatment of respiratory dysfunction by detecting hypoxaemia and is effective in guiding oxygen therapy in both adult and paediatric populations. Pulse oximetry does not provide information about the adequacy of ventilation or about precise arterial oxygenation, particularly when arterial oxygen levels are very high or very low. Arterial blood gas analysis is the gold standard in these settings. Pulse oximetry may be inaccurate as a marker of oxygenation in the presence of dyshaemoglobinaemias such as carbon monoxide poisoning or methaemoglobinaemia where arterial oxygen saturation values will be overestimated. Technical considerations such as sensor position, signal averaging time and data sampling rates may influence clinical interpretation of pulse oximetry readings.

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Pulse oximeters are in common use because they are:

1. non invasive

2. cheap to buy and use

3. can be very compact

4. detects hypoxaemia earlier than you using your eyes to see cyanosis.

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What does a pulse oximeter measure?

•The oxygen saturation of haemoglobin in arterial blood – which is a measure of the average amount of oxygen bound to each haemoglobin molecule. The percentage saturation is given as a digital readout.

•The pulse rate – in beats per minute, averaged over 5 to 20 seconds.

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A pulse oximeter gives no information on any of these other variables:

•The oxygen content of the blood

•The amount of oxygen dissolved in the blood

•The respiratory rate or tidal volume i.e. ventilation

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Oximeters give no information about the level of CO2 and therefore have limitations in the assessment of patients developing respiratory failure due to CO2 retention. On rare occasions oximeters may develop faults and like all monitoring the reading should always be interpreted in association with the patient’s clinical condition. Never ignore a reading which suggests the patient is becoming hypoxic. There is no doubt that pulse oximetry is the greatest advance in patient monitoring for many years and it is hoped that their use will eventually become routine during anaesthesia and surgery worldwide.

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Normal values of pulse oximetry:

In a healthy person, oxygen saturation levels in arterial blood vary between 95 and 100 percent, according to the World Health Organization. A reading below 95 percent in a healthy person with normal lung function indicates low oxygen levels in the blood, a condition medically termed hypoxemia and requires medical investigation. People always want to know what their oxygen saturation “should be”.  A fit, healthy young person will probably have an oxygen saturation of 95 – 99%. This will vary with age, degree of fitness, current altitude, oxygen therapy etc. Normal oxygen saturation for aged 70 and above when awake at rest and at sea level is greater than 94%. In healthy infants and children, mean SpO2 values at sea level have been reported to be 97% to 99% and they might be lower in neonates and young infants (range: 93%-100%). Pulse oximeters can either be used to take a ‘one-off’ reading from someone or can be left on for period of time. A single one-off reading often isn’t much use, trends over a period of time give more information. It is important to remember that pulse oximetry is one way of monitoring breathing. It is also necessary, as a minimum, to record respiratory rate and if pulse oximetry is used the amount of oxygen they are receiving must be recorded. As with all clinical assessments the ‘whole picture’ must be looked at.

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Acceptable normal ranges for patients without pulmonary pathology are from 95 to 99 percent.  Usually, levels of SpO2 range from 96 to 99% in healthy individuals. However, when patients have pulmonary or cardiovascular chronic diseases at the same time as a common cold or pneumonia, the level of SpO2 may drop rapidly. SpO2 lower than 90% is denotes acute respiratory failure. When SpO2 drops by 3 to 4% from its usual level, even if it is not less than 90%, an acute disease may be suspected. In some patients, usual levels of SpO2 may be below 90%. Most other individuals will have fluctuations of 3 to 4%. Depending on individual pulmonary or cardiovascular conditions, the level of SpO2 may be relatively higher at rest, even though the level drops considerably during exercise or sleep. As with “normal” body temperature, the level of SpO2 varies from person to person. Since pulse oximeters may produce errors, there is no “correct” or “incorrect” result. Therefore, it is best to record the individual’s level of SpO2 over a long period, and determine their typical range at rest and at various levels of activity so that abnormal decreases can be detected.

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In the book “Manual of Elderly Home Care by Individual Illnesses,” published by Kinpodo Inc., two key insights into SPO2 rates are provided:

1. The ideal range of oxygen saturation is 96 to 98%. However, since some patients may have lower levels, the person’s normal levels should be determined.

2. If the level is lower than normal, first measure another finger. If the level is 3 to 5% lower than the usual stable level, or lower than 90%, consult your personal physician.

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It is important to remember that pulse oximeters measure and calculate the oxygen saturation of the hemoglobin in arterial blood, not the actual oxygen content of the blood; therefore, they do not provide a measure of actual tissue oxygenation or how well the patient is ventilated. Be cautious interpreting readings when there has been a sudden change in SpO2. One example would be a sudden decrease from 97% SpO2 to 85% SpO2; this is physiologically impossible. Evaluate this information in conjunction with the patient’s clinical condition and limitations of pulse oximetry. Oxygen saturation values below 70% obtained by pulse oximetry are unreliable. Any time hypoxia is suspected, but not confirmed with pulse oximetry, ABGs should be performed. Even when the pulse oximeter reads the SpO2 as normal, the patient could have undetected carbon dioxide retention. Therefore, it is important not to rely on the information from pulse oximeters alone in the assessment and diagnosis of hypoxemia.

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What are low oxygen levels?

Generally, hypoxemia is defined as a SpO2 level less than 95%, with severe hypoxemia being an SpO2 level less than 90% and a PaO2 level less than 70 mmHg. Oxygen saturation levels less than 90 percent should be considered a medical emergency, WHO advises.

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Pulse Oximetry: What do the Numbers mean?

SpO2, % PaO2, mm Hg Oxygenation Status
95–100 80–100 Normal
91–94 60–80 Mild hypoxemia
86–90 50–60 Moderate hypoxemia
Less than 85 Less than 50 Severe hypoxemia

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Circadian Variability of Pulse Oximetry:

Living organisms frequently present changes at the biochemical, cell and/or functional level during the 24h cycle, and the presence of this biological clock is an important advantage for adapting to an environment. The cardiovascular system and the respiratory tract present this type of circadian variation. Nevertheless, one of the possible consequences, which is the circadian modification of SpO2, has not been fully explored. Peripheral oxygen saturation (SpO2) measured by pulse oximetry is widely used in clinical practice, but its fluctuations over the course of the 24h of a day have not been explored at length. In a study done in children who were hospitalized due to non-cardiopulmonary diseases, it was found that SpO2 had a circadian variation. In another study, authors have evaluated whether this phenomenon is also present in clinically healthy children. The results corroborate the fact that there is a circadian variation in SpO2 and that it reaches maximal values in mid-afternoon and minimal values in the early hours of the morning.

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High altitude:

In Denver where the altitude is virtually exactly 5,280 feet, the normal range of pulse oximetry is 94-97% and very acceptable. If you live along or near any of our coastlines (sea level) your “normals” are higher because you are almost literally at sea level. Perhaps a range of 95%-99% would be your normal range. The reason for the difference is due to two values. The first is the percentage of oxygen in the air we all breathe. This one is easy. The percentage of oxygen in “room air” is 21%. Pulmonologists and respiratory therapists know this as the FIO2 or Fraction of Inspired Oxygen. The second value we need to know is the barometric pressure. Barometric pressure (Pb) can be measured in several different ways. In pulmonary medicine the millimetre (mm) of mercury (Hg) is used as reference. At sea level the Pb is normally reported as 760 mmHg. For reference, in Denver, the Pb is normally around 620 mmHg. Since the FIO2 stays exactly the same at 21% up to an altitude of 60 miles, we simply have to multiply the Pb by the FIO2 to see the how much oxygen is available for us to breath at any altitude. This is reported as the PIO2 or the Pressure of Inspired Oxygen. So 760 x 0.21= about 160mmHg is partial pressure of inspired oxygen at sea level, and but in Denver 620 x 0.21= about 130mmHg. That 30 mmHg difference in partial pressure of inspired oxygen can mean a great deal physiologically to patients who require supplemental oxygen. A patient doing well on 2 L/min in Denver, may not need oxygen at all if they travel to Miami which is at sea level.  Healthy individuals at sea level usually exhibit oxygen saturation values between 96% and 99%, and should be above 94%. At 5,280 feet altitude (one mile high) oxygen saturation should be above 92%.

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Normal SpO2 values in paediatrics:

Normal paediatric SpO2 values have not yet been established. Pulse-oximetry readings vary with age and altitude. The substantial variation of normal SpO2 values among studies can be attributed to differences in sample size, instruments used, health of participants, probe positioning, and measurement protocols. Thus, in healthy infants and children, mean SpO2 values at sea level have been reported to be 97% to 99% (−2 SDs, 95%–96%), and they might be lower in neonates and young infants (range: 93%–100%). At moderate altitudes SpO2 values are somewhat lower (mean: 97%–98%; −2 SDs, 93%–96%) and decrease further at high altitudes (>3000 m; mean: 86%–91%; −2 SDs, 74%–82%). Authors of a recent systematic review concluded that supplemental oxygen should be administered to children who reside at altitudes of >3000 m if the SpO2 is <85%. Most children also exhibit a progressive fluctuation in SpO2 during a 24-hour cycle. Maximal values occur in the late afternoon, whereas minimal values appear in the first morning hours. This pattern is evident regardless of whether children are asleep or awake. Basal SpO2 values reported by polysomnography or home monitoring range from 95% to 100%, but normal saturation nadirs can be as low as 84% to 86%.  However, although SPO2 values in the range of 90% to 93% are not uncommon during sleep, they might be associated with poorer academic performance.

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Sleep SpO2 in adults:

Typically normal oxygen saturations are within 94-97% while sleeping.  Patients with sleep breathing disorders, like sleep apnea may experience dips in this saturation. However, it is standard to try and keep saturation above 89%

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Temporary Hypoxemia during Exercise:

When you do any type of strenuous exercise, you will notice that your breath is quickened, your pulse becomes faster, and your lungs expand. All of these are physiological responses that your body makes to meet the much higher demand for oxygen from the muscles, and to prevent you from feeling hypoxic. When you work out, muscles utilize more oxygen and need to draw more oxygen from the blood, creating an oxygen debt which puts you into a temporary state of hypoxemia. Your body will then self-adjust its respiratory and circulatory systems so that it can maximize the oxygen intake and transport abilities to make up for the low blood oxygen saturation. It is normal for your oxygen saturation to drop slightly during exercise, because your muscles are extracting more oxygen to handle the extra activity. However significant drop of SpO2 during routine exercise suggest cardio-pulmonary illness.

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How to improve your Oxygen Levels:

To improve your oxygen level if you are feeling winded, adopt a pursed-lip breathing technique. Breath in through your nose, allowing your inhalation to slow a bit, giving your body the chance to exchange oxygen and carbon dioxide in your blood. Make sure to take a long, deep, full breath as you inhale, and then exhale fully to get rid of the carbon dioxide. Purse your lips as you exhale to allow a controlled amount of air to leave your body at time.

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Types of pulse oximetry:

Pulse oximetry is classified in two ways:

1. Transmissive vs. reflective oximetry

2. Continuous vs. intermittent oximetry

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Transmissive vs. reflective oximetry:

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Currently, the two basic types of pulse oximeter probes are transmission probes and reflectance probes.

Transmission probes:

With transmission probes, the light emitter and sensor are placed opposite each other on pulsatile tissue such as a digit or ear. The lights used to measure tissue oxygenation are typically placed across from a detector surrounding approximately 5-10 mm of tissue that contains pulsatile blood flow, such as a fingertip or ear lobe. In general, the transmission method can only be used on limited areas of the body, such as fingers, earlobes, etc. Furthermore, in some instances when the transmission method is used, physiological conditions such as stress and temperature can affect the accuracy of pulse oximetry readings.

Reflectance probes:

With reflectance probes, the light emitter and sensor are placed side by side on a flat body surface. The detector lies adjacent to the light source on a flat surface such as the forehead. This information can be used noninvasively to help evaluate the hemodynamic status of a patient and to detect hypoxemia in various clinical settings. Vasodilation and pooling of venous blood in the head due to compromised venous return to the heart, as occurs with congenital cyanotic heart disease patients, or in patients in the Trendelenburg position, can cause a combination of arterial and venous pulsations in the forehead region and lead to spurious SpO2 (Saturation of peripheral oxygen) results.

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It is interesting to note that the ratios of the `AC/DC’ ratios at 660 nm and 940 nm (at which many commercial devices operate) are very similar (approximately 0.5) in both reflection and transmission modes. This means that using the same pulse oximeter with either reflection or transmission probes will produce reliable results.

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Continuous vs. intermittent monitoring:

Continuous pulse oximetry monitoring is recommended for patients who:

•have a critical or an unstable airway

•are receiving conscious sedation during diagnostic procedures

•have a condition or history that suggests a risk of significant desaturation

•have known lung dysfunction

•have obstructive sleep apnoea or morbid obesity

•are in acute pain and receiving analgesics at dosages likely to cause respiratory depression

•have cardiopulmonary disorders severe enough to result in at least one documented desaturation episode treated with supplemental oxygen

•are at risk for desaturation at the time of discharge or transfer from an intensive or post-anesthesia care unit

•are undergoing haemodialysis.

Pulse oximetry should to used intermittently when the patient:

1. is on supplemental oxygen,

2. has a tracheostomy and is on long term mechanical ventilation with chronic stable respiratory failure with frequency of measurement dependent on the clinical conditions of a patient.

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Sleep vs. waking SpO2 levels:

With intermittent vital-sign and SpO2 monitoring, a true pulse oximetry reading may never be obtained. A caregiver who approaches a sleeping patient to obtain vital signs may awaken the patient, causing immediate vital-sign changes. Many patients have normal SpO2 levels when awake but decreased levels during sleep. Roughly one-third to one-half of adverse events requiring critical interventions in hospitals are related to altered respiratory function. Thus, high-risk patients should undergo frequent if not continuous pulse oximetry monitoring—especially those with sleep-disordered breathing, as in sleep apnea. When transferred to med-surg floors, patients with sleep apnea, those receiving opioids, and those recently transferred from post-anesthesia care units or intensive care units (ICUs) where continuous SPO2 monitoring is used are at high risk for needing ICU readmission because of the switch from continuous to intermittent vital-sign and SpO2 monitoring. Patients with sleep-disordered breathing are more prone to arrhythmias, myocardial infarctions, and stroke. The nursing staff needs to be able to monitor them more closely to prevent serious adverse events.

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How to use and choose pulse oximeter:

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Ignorance about pulse oximetry:

Several studies show that there’s a knowledge deficit about pulse oximetry among medical and nursing staff. In one study, researchers administered a 17-question survey on pulse oximetry to 442 nurses, physicians, and respiratory therapists; the respondents’ mean score was just 66%. Another study of 50 nursing and medical staff found “an alarming deficit” in their understanding of pulse oximetry.

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Do clinicians know how to use pulse oximetry? A literature review and clinical implications: a 2006 study.

Pulse oximetry has become one of the most commonly used tools in the clinical environment for assessing patients’ oxygenation status. It is employed almost continuously in critical care areas and frequently in the general ward environment. Although it is a much better tool for determining hypoxia than the human eye, its use is limited if clinicians do not understand relevant physiological principles, such as the oxyhaemoglobin dissociation curve and the inherent limitations of the device. Furthermore, the risk for compromised patient safety is significant if clinicians fail to recognise the potential for false or erroneous readings. This paper explores the research which has examined clinicians’ comprehension of pulse oximetry. Fourteen studies examining clinicians’ knowledge of pulse oximetry were reviewed. These studies revealed significant knowledge deficits about pulse oximetry amongst nurses, doctors and allied health professionals, all of whom used this technology frequently. Alarmingly, those lacking an adequate understanding of pulse oximetry included senior, experienced clinicians. Educators and clinicians alike must ensure that a safe level of knowledge for the use of pulse oximetry is maintained in order to ensure that patient outcomes are not compromised.

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Types of pulse oximeters:

Today’s market offers a wide range of Pulse Oximeters available from many well renowned companies.  If we are to look for the available models in circulation, it could be broken down into two large categories; one would be fingertip type and the other the handheld model.  The handheld pulse oximeter has become a vital instrument in the care of infants, children and adults with cardiopulmonary diseases. It is an accurate, simple and non-invasive method of measuring arterial oxygen saturation. The handheld pulse oximeter provides an easy and accurate way to monitor the blood oxygen saturation and pulse rate. The size, simplicity and convenience of this pulse oximeter are favorite features among many professionals. The handheld pulse oximeter makes use of a probe, which is placed in the person’s finger or earlobe and the reading appears on an easy-to-read liquid crystal display (LCD). The hand-held pulse oximeter is designed for monitoring neonatal through adult patients in almost any setting, from hospital to home, although it is more appropriate in a clinical setting than in the home. It is ideal for spot checks or continuous monitoring. The fingertip model is a small, cost effective pulse oximeter accurately measures blood oxygen saturation levels and heartbeat pulse rates on adult patients. It’s a very compact and self-contained unit to which you need to simply slip the finger. Seconds afterward, it will display your data on high quality easy-to-read liquid crystal display (LCD). The fingertip pulse oximeter is very simple to use and since there is no special learning needed to use it without any setting up, calibration or adaptive devices, it is ideal for use in the hospital or clinical environment, during an emergency or patient transport, or for in-home use as well. The portability of the fingertip pulse oximeter makes it a very popular choice for home use, sports personals, aviators and for medical professionals who are always on the move, it brings a whole new cost effective solution for spot-checking and short term monitoring.  A new addition to the fingertip model would be the Paediatric Finger pulse oximeter designed especially for children weighing 5-40kg used for spot-check of oxygen saturation and pulse rate.

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What to look for in a Spot-Check Oximeter?

Finger pulse oximeters are ideal for spot checks and are portable, battery operated and user friendly. However, other factors should be considered, such as confidence in the reliability of the oximeter long-term as well as the belief in the accuracy of the device in challenging patients. A lot of oximeters are on the market, and any oximeter may work well on a certain patient, but it is the challenging patient population like those with chronic conditions who require the most accurate data to aid in better and faster decision making. Patients with chronic diseases usually suffer from low blood flow (e.g. perfusion), which can impact accuracy. It is important to ask the manufacturer for proven accuracy claims backed by evidence such as published clinical papers. Good pulse oximeters will have specific labelling for challenging conditions.

Here are some factors to consider:

Ideal Features and Functions for Spot-Check Oximeters:

Feature

• Small and portable

• Lightweight

• Easy to use: automatic on/off, simple battery changes, easy-to-read results

• Flexible fit—all finger sizes from adult to paediatric

Function

• Reliable—meets ±2% accuracy with proven clinical data

• Works with a variety of blood pressures and perfusion levels

• Accurate to 70% saturation

• Accurate with some motion

• Durable—able to withstand drops and some moisture

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Oximeters are also classified as per technological features:

1. Best value

2. Oximeter with pleth-graph

3. Oximeter with pleth graph and alarm

4. Oximeter with continuous recording and memory (sleep study, exercise)

5. Pulse oximeter with Bluetooth support

6. Patient with very low blood perfusion

The best value category gives you well-built units with basic functions (pulse rate and blood oxygen saturation level). Any one from this category will serve you well unless you want more features or have special needs. Two most common features for oximeters are pleth graph and alarm. The pleth graph gives an indication of the change in volume of blood flow as the heart beats. The alarm gives an audio or visual signal when either the oxygen or pulse rate exceeds the normal range. Pleth graph is very useful to older patients. The plethysmograph can tell something about the condition of the patient’s heart, such as missing or irregular heartbeats, low blood flow… There are oximeters available if the patient has very poor blood circulation and more tolerant of motion.

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Pulse Oximeter Usage:

The pulse oximeter consists of a peripheral probe, together with a microprocessor unit, which displays a waveform, the calculated oxygen saturation percentage, and the averaged pulse rate. Alarms are available which sound when a low SpO2 level is detected, or when the pulse rate is either tachycardic or bradycardic. The probe of the device must be positioned in such manner that the emitter and the detector are exactly opposite to each other with 5 to 10 mm of tissue between them. Typical measuring sites include the finger, the toe, the pinna, and the lobe of the ear, whereas for neonates and infants measurements are commonly obtained from the palm or the sole by using specially designed probes. Less commonly used sites are the cheek and the tongue. The probe must be placed on a pulsing vascular bed. A sharp waveform with a clear dicrotic notch indicates a good signal. The machine then reads and averages the values that the waveform receives from the vascular bed, which are read over 5 to 20 seconds, depending on the machine’s internal setting. Averaging the signal reduces erroneous readings and distinguishes artifact from true signal. A pulse rate and percentage of oxygen saturation are interpreted from these averaged values.

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Correct use of the pulse oximeter includes proper placement of the probe. The emitter and detectors must be opposite each other, and light must not reach the detector other than through the tissue. Care must be used to ensure that the digit is fully inserted into the probe. Older products used a sensor cable that attached to a base pulse oximeter. Modern designs digitize the signals within a single enclosure, negating the need for a base unit in many cases. A modern design will also optionally feature a standardized wireless interface like low-power Bluetooth to send data to a capture or display device like a tablet or smartphone.

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Proper probe position:

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Improper probe position:

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The finger should be the first choice of site used for measurement. A nondisposable clip-type probe is adequate for most purposes, especially when a single or spot reading is being taken. Self-adhesive probes are more useful for long-term monitoring or when motion artifact is expected. Toes may be used instead of fingers, but poor signal because of decreased perfusion is more likely. The lobe or pinna of the ear can be used with a clip-type probe. Care must be taken when using the ear so that pressure from the clip does not impair perfusion. Forehead or nasal sensors may also be used but, depending on clinical area of use, may not be as readily available as finger probes.

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What is the best location for the pulse oximeter probe?

Choose a site with the best pulsatile vascular bed: the finger, toe, ear lobe, and bridge of the nose have been used. In infants, flexible probes work through the palm, foot, penis, or arm. The cheek or wing of the nostril have also been used. However, overall performance of finger probes is generally found to be better than performance of probes at other sites. Nose and forehead probes perform poorly when SpO2 is low. Manufacturers generally recommend use of the foot for infants.

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When placing probes on fingers or toes, remove nail polish, especially blue, black, green, brown/ red, or synthetic nails; or place the probe sideways on the finger. Synthetic nails and some colors of nail polish may result in errors of 3% to 6%. In addition, SpO2 values may be lower in dependent extremities than in nondependent sites. Blood flow to the extremity where the sensor is placed should not be impeded in any way. The sensor should be placed on the extremity opposite arterial lines and noninvasive blood pressure monitoring devices so that pulsatile flow is not interrupted.

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Approach Considerations:

There are several approaches to pulse oximetry.

Digit approach:

This is the preferred method. The transmission probe is placed on the end of a digit, usually the finger, with the emitter on one side and the sensor on the opposite side (see image below). The digit should be resting comfortably and out of excessive light. The probe is then connected to the monitoring unit. Excessive debris should be removed prior to probe attachment, as well as any nail polish or artificial nails.

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Ear approach:

A transmission probe is placed on the end of an ear lobe with the emitter on one side and the sensor on the opposite side (see image below). The probe is then connected to the monitoring unit.

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Palm/foot approach in neonates:

In neonates, in whom the digit or ear may be too small, a transmission probe may be placed over the palm or foot. The probe is then connected to the monitoring unit.

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Forehead approach:

A reflectance probe should be placed low across the forehead right above the eyebrows and away from a major vessel (see image below). The patient should be resting in an inclined position. A headband around the probe and across the forehead should also be placed. The probe is then connected to the monitoring unit.

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Pulse oximeter probes. A comparison between finger, nose, ear and forehead probes under conditions of poor perfusion: a 1991 study:

The performances of 10 pulse oximeters using finger probes were compared with the same pulse oximeters using alternative probes (eight finger probes, two nose probes and a forehead probe) in poorly perfused patients. All readings were then compared with directly measured arterial blood oxygen saturations. The mean difference (bias, ‘accuracy’), standard deviation (precision) and ‘drop out’ rate for each pulse oximeter combination was determined. An overall ranking of performance of each pulse oximeter was calculated using five criteria (accuracy, precision, number of readings within 3% of standard, percentage of readings given within 3% of standard, expected overread limit in 95% of cases). Nose and forehead probes performed poorly. Some ear probes performed well compared to some finger probes, but the overall performance of probes in other sites compared to finger probes was worse, (p = 0.05). Two of eight ear probes and no nose or forehead probes would be expected to be within 4% of the reference value in 95% of readings. The use of finger probes rather than probes in other sites is recommended in the patient with poor peripheral perfusion.

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Pulse oximetry has gained wide clinical acceptance in many areas. Small portable systems are available for use virtually anywhere. Almost every patient that has oxygen or mechanical ventilation requirements would benefit from clinical monitoring of their oxygen status by pulse oximetry. This may be in the form of continuous monitoring or by intermittent testing. The oxygen saturation as calculated by pulse oximetry has a 95% confidence rate of ±4%, so oximetry is considered to be reliable at readings that range between 70% and 100% SpO2. This means that, although pulse oximetry is not a replacement for blood gas testing, it can be used as a screening tool when poor oxygen saturation is suspected.

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Performing pulse oximetry:

1. Turn the machine on and allow for self-tests

2. Apply probe to patient’s finger or any other digit as recommended by the device manufacturer

3. Allow machine to register saturation level

4. Record time and initial saturation percent on room air if possible on/with the patient care report (PCR)

5. Verify pulse rate on machine with actual pulse of the patient

6. Monitor critical patients continuously until arrival at the hospital. If recording a one-time reading, monitor patients for a few minutes as oxygen saturation can vary

7. Document percent of oxygen saturation every time vital signs are recorded and in response to therapy to correct hypoxemia

8. In general, normal saturation is 95-99%. Below 95%, suspect a respiratory compromise.

9. Use the pulse oximetry as an added tool for patient evaluation. Treat the patient, not the data provided by the device.

10. The pulse oximeter reading should never be used to withhold oxygen from a patient in respiratory distress or when it is the standard of care to apply oxygen despite good pulse oximetry readings, such as chest pain

11. Factors which may reduce the reliability of the pulse oximetry reading include:

• Poor peripheral circulation (low blood volume, hypotension, vasoconstriction, hypothermia)

• Excessive pulse oximeter sensor motion

• Fingernail polish (may be removed with acetone pad)

• Carbon monoxide bound to hemoglobin

• Irregular heart rhythms (atrial fibrillation, SVT, etc.)

12. To improve quality of signal, hold finger dependent and motionless (motion may alter results) and cover finger sensor to occlude ambient light.

13. Assess site of oximetry monitoring for perfusion on a regular basis, because pressure ulcer may occur from prolonged application of probe.

14. Document inspired oxygen or supplemental oxygen and type of oxygen delivery device.

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Nursing considerations and care:

Choose sensor appropriate for the client’s size and location to be used (finger, toe, and ear). Inappropriate size or device may cause inaccurate results or pain. Remove any finger nail polish or artificial nails on the fingers to be used if possible. The sensor may be unable to provide an accurate reading through nailpolish or acrylic nails. Using alcohol ensures that the site and the sensor are clean and dry. Place the adhesive sensors and finger clip. Appropriate location ensures accurate sensor for adults on the client’s index, reading. middle or ring finger. Adhesive sensor also can be placed on client’s toe. A small earlobe clip is available for use on small adults, children’s, and infants. If necessary place newborn adhesive. Decreased circulation could skew result, check the client proximal oxygen saturation readings, pulse and capillary refill. Check the sensor’s markings and if sensor’s are not aligned, make sure the light emitting diode sensor and photo detector are correctly aligned, they should be opposite each other. The continuous pulse oximeter gives audible and visual alarms. Setting the alarm ensures notification to the nurse if the client values are out of the desired range, indicating the possible problem that requires intervention. Move an adhesive sensor every 4 hours and a clip type sensor at least every 2 hours. Watch for signs of tissue breakdown or irritation from adhesives or clips. Moving the sensor helps to prevent tissue irritation and necrosis. Clean the sensor with alcohol wipes when it is removed. The American Association of Critical-Care Nurses (AACN) recommends assessing the prospective site for signs such as cyanosis, decreased peripheral pulse, and decreased temperature, as these can indicate diminished blood flow and lead to inaccurate SpO2readings. The AACN further recommends reevaluating the sensor site periodically. When using disposable sensors, assess the site every two to four hours and replace the sensor every 24 hours. When using a reusable sensor, the site should be checked every two hours and changed every four hours. With reusable sensors, the manufacturer’s recommendations regarding cleaning agents should also be followed.

Special reminder:

• Documentation includes each oximeter reading and location of the sensor.

• If the client is not receive oxygen, the reading is documented “on room air”

• Document if the client is receiving supplemental oxygen and if so, how much (e.g. O2 at 3 l/m)

• Report any downward changes in oxygen saturation of 3% to 5%.

Remember: Values obtained by pulse oximetry are unreliable in the presence of vasoconstricting medications, IV dyes, shock, cardiac arrest, severe anemia, and dyshemoglobins (e.g., carboxyhemoglobin, methemoglobin).

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Sensor size:

Sensors are sized according to the patient’s weight; different manufacturers specify somewhat different ranges. It’s important to use the correct size to avoid skin complications and ensure accurate readings. Even when the correct size is used, skin breakdown at the placement site, caused by pressure from the sensor, has been reported.

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Adult sensor/probe:

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Neonate sensor/probe:

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Check that the right type of sensor is being used. The sensor site should be chosen based on which location has the best pulsatile vascular bed. Generally the finger is chosen first; however, forehead sensors are particularly useful in patients with poor peripheral circulation.  Forehead sensors are also a good alternative in patients under general anesthesia whose extremities aren’t readily accessible. To exclude motion artifact caused by shivering, patients should be kept warm. A study of trauma patients during prehospital transport found that those actively warmed with resistive heating blankets had significantly fewer oximeter alarms than those given wool blankets. The researchers attributed this to improved peripheral circulation in the actively warmed group. To avoid potential interference from ambient light, the sensor can be covered with the patient’s linens. Nail polish or artificial nails should be removed.

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Some Pointers for Nurses:

Here are some important things to keep in mind when using a pulse oximeter:

• Ensure that continuous monitoring is used only on patients whose condition requires it, such as patients with a compromised airway. If your patient has an inappropriate order on the chart, alert the prescriber and ask that it be updated.

• Be aware of situations for which pulse oximetry is contraindicated, such as during CPR.

• Know causes of erroneous readings, such as movement or carbon monoxide poisoning.

• Choose the correct sensor size for the patient.

• Check the skin under the sensor and rotate the sensor site periodically.

• Explain the equipment and the reasons that alarms might sound to patients and family members, to reduce their anxiety.

• 100% oxygen should be administered to all patients despite a good SpO2 if they have respiratory distress

• Make sure that all dirt and nail polish or any obstructive covering is removed to prevent the unit from giving a false reading

• Attempt to obtain a room air reading and a reading with supplemental oxygen

• Do not read while BP being taken as it may give false readings

• Although the pulse oximeter displays the heart rate, the unit should not be used in place of the cardiac monitor and a physical assessment of the heart rate

• Many patients with COPD have chronic low oxygen readings and may lose their respiratory drive if administered prolonged high oxygen therapy; routinely assess pulse oximetry as well as respiratory drive when administering oxygen to these patients; do not withhold oxygen from any patient that requires it.

• The room air pulse oximetry reading is not required if the patient has been placed on supplemental oxygen prior to EMS arrival

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Treatment guidelines:

SpO2 Reading Interpretation Action
100% to 95% Ideal Range No supplemental oxygen is needed
95% to 90% Mild to Moderate Hypoxemia Check airway, start oxygen therapy via nasal cannula at 4-6 l/m
90% to 85% Severe Hypoxemia Check airway, start aggressive oxygen therapy, high flow oxygen via nonrebreather mask at 15 l/m. Consider bag valve mask ventilation with 100% oxygen if the patient does not have adequate ventilations.
85% to less Respiratory Failure Assist ventilations with 100% oxygen and bag valve mask; consider CPAP or intubation

1. All patients who require vital signs to be taken should have oxygen saturation measured and recorded as part of the vital signs

2. Measure oxygen saturation before applying oxygen and repeat the measurement after oxygen has been applied, do not delay oxygen administration in patients experiencing severe respiratory distress

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How do I clean/sterilize the probe after use on one baby and before being used on another?

Cleanse the probe with alcohol; let it dry before using on another baby.

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Improving an oximeter signal:

Warm and rub skin

Apply a topical vasodilator – e.g., glyceryl trinitrate (GTN) cream

Try an alternative probe site

Try a different probe

Try a different machine

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Using Pulse Oximeter with Cold Hands:

Pulse oximeter usually runs slow, if at all, in a cold environment. Cold hands and fingers mean that the blood flow and circulation to your hand is reduced and may cause problem for the oximeter to detect a good pulse signal. When this happens, a pulse oximeter may take several minutes to return a reading and sometimes the reading may be inaccurate. Under this situation, try to warm up the patient’s hands prior to taking a measurement. One good way is to massage patient’s hands by rubbing them gently against each other. Doing some hand exercise would also increase blood circulation.

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Challenges of pulse oximetry:

One drawback of continuous pulse oximetry monitoring may be the cost of integrating it into a central monitoring system. Others include false alarms, staff complacency with alarms, and patient-related issues, such as limited ambulation, failure to keep sensors on, or failure of sensors to read properly. Many of these problems can be addressed when implementing a monitoring program.

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False alarms:

Patient movement and low perfusion can increase false alarms and cause erroneous measurements. Also, if the oximetry sensor is placed on the same side as an automatic inflatable blood pressure cuff, a false alarm may sound when the cuff inflates. Frequent false alarms can cause “alarm fatigue” in caregivers. Hearing the same alarm go off or hearing frequent alarms on specific patient leads can desensitize nurses to alarms and cause them to miss significant true alarms. Also, use of the monitor may lead them to focus more on the monitor than the patient. In addition, false alarms may require staff interventions that interfere with patients’ sleep, and can cause anxiety in patients and families. Bedside equipment alarms can be frightening to patients and families, especially if they aren’t attended to promptly. Quality assurance studies conducted by member hospitals of the Child Health Corporation of America’s Pulse Oximetry Forum indicate that in paediatric populations, the false alarms that occur during continuous pulse oximetry cause needless anxiety for patients and families. Nurses should explain why pulse oximetry is being used, how it works, and what the readings indicate in language the patient and family can comprehend. The factors that can lead to false alarms should also be explained, as should the importance of frequent site assessment and rotation. Finally, nurses can remind prescribers to change the order from continuous monitoring to intermittent, as appropriate. Newer pulse oximetry technologies (sometimes called “smart” technologies) are designed to decrease false alarms, increase the reliability of true alarms, and alert clinicians to patterns or trends that give early warning of respiratory decompensation. Consider, for example, a patient with sleep apnea: If the patient stops breathing for several seconds, the SpO2 value may remain in the normal range or rise above the alarm limit range; or it may be slightly below the alarm range and then return to normal. In this case, the alarm may not sound because the time limit wasn’t violated; if the alarm does sound, the nurse might consider it a false alarm because it occurred only momentarily. With newer technology, the repeated pattern of lower SPO2 value and alarm violation alerts the staff to review the patterns and assess the patient further. Also, some newer oximetry systems have visual graphs that show the length and degree of desaturations, which are more telling than a single number or trend.

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Home use:

Technology can be slow and initially expensive, so the use of pulse oximeters at home is just getting started. But if we have a need for a pulse oximeter, they are now easy to obtain and reasonably priced. If you are buying one on your own, you need to look at the specifications and what it will measure. If you have a heart condition and you know your oxygen saturation is usually 85%, you don’t want to get a pulse oximeter that only measures 90 to 100% accurately. A good home pulse oximeter should measure 70% and above with good accuracy.  Having a monitor at home can be important for many people. If saturations vary within the normal range, that is typical and okay. But if, for example saturations are in the range of 94% and your child takes a brisk walk and returns short of breath with saturation readings at 86%, then we need a doctor to assess those numbers and decide if an action or treatment is necessary or if there is a problem that needs addressed medically. We can only track this over time if we have a home pulse oximeter. In summary, using a pulse oximeter at home is a quick, easy, inexpensive way to track oxygen saturation.

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For patients on long-term oxygen therapy, pulse oximetry arterial oxygen saturation (SpO2) measurements are unnecessary except to assess changes in clinical status, or to facilitate changes in the oxygen prescription.  Home pulse oximetry is also indicated when there is a need to monitor the adequacy of SpO2 or the need to quantitate the response of SpO2 to a therapeutic intervention.

Consider a pulse oximeter for home use for the following indications:

A. To determine appropriate home oxygen liter flow for ambulation, exercise, or sleep;

B. To monitor individuals on a ventilator at home;

C. When a change in the individual’s physical condition requires an adjustment in the liter flow of their home oxygen needs;

D. When weaning the individual from home oxygen;

E. For interstage monitoring of children undergoing the Norwood procedure for hypoplastic left heart syndrome.

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Experimental and investigational indications of pulse oximetry at home include:

A. Asthma management

B. Diagnosing nocturnal hypoventilation associated with neuromuscular disorders

C. Evaluating and teaching continuous positive airway pressure (CPAP)

D. When used alone as a screening/testing technique for suspected obstructive sleep apnea.

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Pulse Oximetry Tips for Home Use:

Once you purchase a home pulse oximeter, take it with you to your doctor’s office for further operating instructions. With your doctor’s approval, you can work together to learn how to adjust your oxygen flow based on your fluctuating oxygen saturation levels.

Additionally, keep in mind the following tips before you start to use a pulse oximeter at home:

•Monitor and keep a log of your oxygen saturation levels at various times during the day and during specific activities. Share them with your doctor so she can get a better understanding as to how rest and activity affect your oxygen saturation levels.

•Work carefully with your doctor to develop a target oxygen saturation level. Under the instruction of your doctor, adjust your oxygen flow rate to maintain your target oxygen saturation level.

•Never titrate oxygen without specific instruction from your health care provider.

•Never rely on a pulse oximeter to determine how you should be feeling. If your oxygen saturation level is normal but you are severely short of breath and/or are experiencing other troubling symptoms, seek emergency medical attention and notify your health care provider as soon as possible.

•A sudden drop in oxygen saturation can be a sign of trouble. Call your doctor as soon as possible if your normal oxygen flow rate fails to maintain your target oxygen saturation level.

• You can use your oximeter at rest or during activities, such as walking or other exercise. However, your oximeter should not be submerged in water.

• Do not smoke! Smoking reduces the amount of oxygen reaching your tissues—while the oximeter will falsely suggest that oxygen level is satisfactory.

• A sudden drop in your oxygen level—for example during a severe cold or the flu—can be a sign of trouble. Call your doctor if your normal oxygen setting is no longer maintaining your saturation and you feel sick. Also, call your supplier if you feel your oxygen system is not working.

• A high resting pulse rate of greater than 100 or a low pulse of less than 40 (check with your doctor to determine your individual pulse ranges) are also reasons to call your doctor.

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How to buy a Home Pulse Oximeter:

Common features:

1. FDA Certified: Pulse oximeter is a class II device and FDA registration is required before selling in US. Although almost all oximeters for sale on the market are now certified, this was not the case a few years ago. You can verify the certification by going to the FDA Medical Device Data Base and enter the manufacturer name in the search field to find out for sure.

2. Accuracy and reliability: The primary purpose of a pulse oximeter is to measure your oxygen saturation (SpO2) and pulse rate. So the key selection criterion is to find one that produce accurate results within its operating range consistently and reliability. Pulse oximeters generally use similar mechanisms for reading data and differ in how they are manufactured. If you need an accurate reading, you should validate your pulse oximeter by comparing it with others, such as those in your doctor’s office or medical clinics. Most oximeters can take a reading within a few seconds and have an accuracy of ±3%. The accuracy is often affected by motion. If your hand trembles, find a model that is more tolerant to hand movements or hold your hand still while taking readings.

3. Ease of use: Fingertip pulse oximeters operate by inserting your finger into the sensor and then pressing one button. They are easy to operate. Make sure the display is large enough for you to read. Some can display the data in different ways making them easier to read.

4. Sensor size: Make sure you can insert your finger comfortably in the sensor. This is normally not an issue for clip-on type. For children and persons with small hands, consider a paediatric pulse oximeter.

5. Other features: There are other features, non-essential, but will assist you in using the oximeter:

•Memory: Save previous readings and timestamps; generate various statistics.

•Computer interface: Save readings to a computer for further analysis by you or your doctor.

•Software program: Analyze the data.

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Pulse oximetry increasing usage:

According to a report by Frost & Sullivan entitled U.S. Pulse Oximetry Monitoring Equipment Market, US sales of oximeters were worth $201 million in 2006. According to a report by iData Research the U.S. pulse oximetry monitoring market for equipment and sensors was over 700 million USD in 2011. In 2008, more than half of the major internationally exporting medical equipment manufacturers in China were producers of pulse oximeters. In June 2009, video game company Nintendo announced an upcoming peripheral for the Wii console, dubbed the “Vitality Sensor”, which consists of a pulse oximeter. This marks the onset of the use of this device for non-medical, entertainment purposes.

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An estimation of the pulse oximetry gap:

No study has ever quantified the extent to which pulse oximetry devices are available to operating room personnel in low and middle-income countries. Even basic information such as the number of operating rooms and the types of monitoring devices is lacking. Anecdotal evidence suggests the presence of an enormous and pervasive “pulse oximetry gap,” defined as the number of pulse oximeters needed to achieve 100% penetrance in a given setting. To estimate this “gap,” other data sources must be examined. We must first estimate the total number of operating rooms in resource-constrained settings. This will give us a sense of the “operating room market.” Once this market is estimated, the gap in pulse oximeter availability can be evaluated. Given the universal use of pulse oximetry in high-income countries, the gap is assumed to be present predominantly in low and middle-income countries.

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Pulse oximetry market:

The table above shows that pulse oximetry penetrance is low in low income countries.

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As demonstrated by the population-based estimate in table above, which exceeds 1 million pulse oximetry devices, the hospital bed and operative volume approaches probably both underestimate the true pulse oximetry market. They do not take into account labor rooms, post anaesthesia recovery rooms, emergency rooms, intensive care units, and other areas where pulse oximetry clearly has a place in clinical evaluation and monitoring. They also do not account for the future market as surgical services increase in the developing world. There is a vast distance between what is currently provided and what is actually needed in terms of surgical services in much of the developing world. As countries address the shortfall of surgical services, the need for and use of pulse oximetry for safe anaesthesia monitoring will need to increase in parallel.

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Functions, uses and indications of pulse oximetry:

The basic rationale behind pulse oximetry is that hypoxaemia may be detected early and treatment can begin before serious or irreversible adverse effects occur. A pulse oximeter is a device intended for the non-invasive measurement of arterial blood oxygen saturation (SpO2) and pulse rate. Oximeters are widely used in hospitals, medical clinics, operating rooms, and homes. Both oxygen saturation level and pulse rate are vital signs of a patient. Oximeters are inexpensive and can report an accurate reading within seconds. Speed is important especially in an emergency situation. Pulse oximeter is used medically by patients with asthma, emphysema, chronic obstructive pulmonary disease (COPD), and other respiratory conditions. Patients with serious respiratory problems should have their SpO2 levels check regularly and especially if they are not feeling well. For many patients, doctors often recommend exercise to improve their physical state. However exercise can result in increasing shortness of breath, patients should monitor their oxygen saturation with pulse oximeters while exercising so they can adjust the pace as the oxygen saturation decreases. Patients with serious cardiac condition would often experience low SpO2 levels. Pulse oximeters would help them to monitor their conditions and use supplementary oxygen when required. Pleth graph produced by a pulse oximeter shows the change in blood volume during a heart pulse is often a good indication of certain heart conditions. Pilots, mountain climbers and people in high altitudes also use pulse oximeters to help guard against hypoxia. Proper breathing techniques, such as pursed lip breathing, can increase your oxygen saturation level. Lots of patients with low oxygen saturations are able to increase their saturations all the way up to 93% with good breathing techniques. Practice and pulse oximeter will help patients to achieve this level of efficiency. Pulse oximeter can also help athletes in high altitude training. The reduction in oxygen level can increase red blood cells in athletes and help to increase his/her endurance.

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Functions of pulse oximeter:

Do remembering that the Pulse Oximeter measures a very important parameter of our body, that is important in ensuring our survival, the pulse oximeter take not only a prominent role for diagnosis in the medical field but also a great beneficial role for sports personals and pilots. With the development of the microprocessor and better sensor, the Pulse Oximeter has stepped into a whole new dimension and gained great acceptance in its clinical application may it be in the hospital institution or at home. If we are to break down the uses of a Pulse Oximeter from a clinical point of use, it could be stated that the any patient with unstable oxygenation has significant benefits from this device, this includes patients at the intensive care unit, at operations, recovery, and hospital ward setting. The general assessment of a patient’s need for oxygen is the most essential part in maintaining life as life cannot continue in the absence of oxygen. Therefore the pulse oximeter plays an important role as a general condition assessment device just like one that checks blood pressure, sugar levels and temperature. The pulse oximeter aids in other patient condition evaluation such as blood flow assessment, cardiopulmonary arrest, asthma and seizures. Because of its simplicity, versatility and speed, pulse oximeters are of critical importance in emergency medicine and more of a necessity for patients with respiratory and cardiac problems, for diagnosis of some sleep disorders such as apnea and hypopnea. It has definitely become a gold standard of use in ambulances, patients under anesthesia, neonates in the intensive care, newborn nurseries and delivery suites; the pulse oximeter serves an important role in transport internally within the hospitals and externally in the ambulance and Air transport. The function and role of the pulse oximeter could not be forgotten from a general diagnostic value as it is very useful in the initial staging of diagnosis as in PFT lab, exercise lab and the sleep lab. Finally it has a great use as an all-purpose assistant and aids in sub-acute care centers and home care patients being an indicator when supplement oxygen should be administered to the patients. The use of the Pulse Oximeter is not constrained to the medical institution, the non-medical oximeters are rather sporty versions of the pulse oximeter designed specifically for high altitude performance sports and the aviator market. Often coming as fingertip pulse oximeters, they are designed to provide correct blood Oximetry and pulse rate measurement while in motion. At higher altitude, it should be noted that blood oxygen saturation decreases because of reduced amount of oxygen in the air; this makes the finger pulse oximeter a very versatile piece of instrument allowing you to accurately assess how well you are adapting to high altitude, by measuring your saturated blood oxygen content and heart rate. Portable, battery operated pulse oximeters are very useful for pilots operating in a non-pressurized aircraft above 10,000 feet where supplemental oxygen is required. Prior to the oximeter’s invention, many complicated blood tests needed to be performed. Portable pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise.

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Uses of pulse oximetry:

The use of pulse oximetry for patient assessment and monitoring is well established in critical care, anesthesiology, and emergency departments.  In recent years, the availability of small, user-friendly, portable and affordable pulse oximeters, including those worn on the finger-tip has opened up the potential for use of this technique in an expanded variety of clinical settings, including primary care. In most countries, oximeters are only sold to patients under the guidance of a licensed healthcare professional, and use by patients should be supervised by their physicians or other qualified health care provider. Incorrect or inappropriate use of oximeters will not provide useful information, and they should be used as part of a broader clinical assessment and not in isolation. Examples of the use of pulse oximetry to monitor a patient’s clinical status include apnea monitoring, evaluation of periodic breathing (in infants), during transport (in the hospital or prehospital setting), and in critical care areas (e.g., the intensive care units and the ED). Pulse oximetry is used during airway procedures (e.g., intubations) and during lumbar punctures and other invasive procedures, (e.g., central lines), especially in infants. Pulse oximetry is used for monitoring patients on mechanical ventilation.  In patients with an endotracheal (ET) tube, pulse oximetry may be a clue to a misplaced or blocked ET tube. The most beneficial use of a pulse oximeter in an anesthetized or ICU patient is as an early warning device for hypoxemia. During anesthesia, this most commonly happens during induction and recovery. It can also indicate the continued need for oxygen supplementation. A study determined that pulse oximetry provided the first warning of an incident in 27% of situations. Additionally, the number of unanticipated intensive care unit admissions decreased after the introduction of pulse oximetry.  Other applications for use of pulse oximetry include controlling oxygen supplementation, monitoring circulation, determining systolic blood pressure, and monitoring vascular volume.

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Pulse oximeters are now used routinely in critical care, anaesthesiology, and A&E departments, and are often found in ambulances. They are an increasingly common part of a GP’s kit. Pulse oximetry’s role in primary care may include:

• Diagnosing and managing a severe exacerbation of chronic obstructive pulmonary disease (COPD) in the community.

• Grading the severity of an asthma attack. Where oxygen saturations are less than 92% in air, consider the attack potentially life-threatening.

• Assessing severity and oxygen requirements for patients with community-acquired pneumonia.

• Assessing severity and determining management in infants with bronchiolitis.

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Clinical uses of pulse oximetry:

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Indications for pulse oximetry are categorized into three groups:

1) A baseline indicator or monitor of a patient’s oxygenation status,

2) Evaluation of response to therapy, and

3) Monitoring during procedures.

Pulse oximetry is indicated in patients with cardiopulmonary disease; unstable or critically ill patients;  and patients with or the potential for apnea, hypoxia, respiratory distress/failure, or shock. Pulse oximetry has been used in the diagnosis of numerous cardiopulmonary diseases and to evaluate the response to treatment in various cardiopulmonary disorders ranging from asthma, chronic obstructive pulmonary disease, bronchiolitis, and reactive airway disease, to pneumonia, airway obstruction, heart failure, and cyanotic congenital heart disease.

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Indications for pulse oximetry include the following:

• Patients with suspected hypoxemia

• All cases of respiratory distress

• For the treatment of primary respiratory or cardiac disease

• All cases of altered or depressed level of consciousness

• Drug overdoses

• Any patient requiring intubation or BVM support

• Major trauma

• Smoke Inhalation (may not be accurate due to CO)

• Any patient on home oxygen, home ventilator, or BiPAP

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Where pulse oximeter is used:

Initially, pulse oximeters gained wide acceptance in hospital operation and anaesthesia rooms. Equipment used for patients in acute condition includes stationary pulse oximeters and bioinstrumentation systems which can simultaneously monitor other important vital signs, for example when using an electrocardiogram. During post-operational recovery or in subacute phases, telemetric, hand-held monitoring units are fixed to the bedside in addition to the stationary pulse oximeter. This equipment is used to warn of sudden deterioration of a patient’s condition. Meanwhile, small portable pulse oximeters are frequently used both in hospitals and for outpatient care.

The following section describes where small, portable pulse oximeters are used.

1. Hospitals:

Small, portable pulse oximeters are used in hospitals, especially by nurses in respiratory and cardiovascular wards. The main purpose is to monitor the vital signs of hospitalized patients. SpO2 is the fifth most important vital sign monitored, after pulse rate, body temperature, blood pressure, and respiration. It is monitored in the morning, afternoon and evening in order to check patient conditions.

2. Outpatient:

The pulse oximeter is used mainly in respiratory departments. Some physicians use the pulse oximeter to monitor SpO2 of patients who are suspected of having respiratory diseases in order to learn their normal values. They then use the values as reference data if the patient’s condition deteriorates.

3. Respiratory function tests and rehabilitation in hospitals:

The pulse oximeter is used for examination and assessment of respiratory function tests and walking tests. These tests may be conducted by laboratory technicians or physical therapists. The device is also used by physical therapists for risk management during patient rehabilitation to confirm a decrease in SpO2 and an increase in pulse rate as needed.

4. Clinics (Clinical internists):

Hypoxemia involves the respiratory, cardiovascular, and nervous systems. The pulse oximeter is used in the field of respiratory internal medicine and general internal medicine, and can determine the necessity of sending patients to specialist hospitals. It can also make differential diagnoses and analyze the severity of a condition. At the same time, the portable pulse oximeter is an essential device for home-visit medical service.

5. Home visit nursing:

Most patients receiving home visit nursing service are elderly. Generally they have some respiratory or cardiovascular system difficulties even if respiratory disease is not the main cause of their problems. SpO2 measurement has been widely used by home visit nurses as a method to quickly assess their patients’ respiratory and cardiovascular conditions.

6. Eldercare facilities:

Pulse oximeter use in eldercare facilities has not yet reached the level of usage by home visit nurses. However, it is expected that the devices will become more widely accepted for vital sign monitoring of patients in hospitals and daycare facilities, especially during those times (often during the Night) when their condition may deteriorate.

7. Other situations:

When the air pressure drops, the partial pressure of oxygen in the air decreases resulting in a decrease in oxygen saturation. The pulse oximeter is used to prevent accidents that might occur during flight and high altitude climbing. Patients receiving HOT (home oxygen therapy) who travel by air or participate in mountain climbing events are often equipped with small, portable pulse oximeters, as are many airliners and organzations involved in high attitude sports and hypoxic training.

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Common Areas for Use of Pulse Oximetry:

1 During anesthesia and postanesthesia care, including both general and conscious sedation

2 Intensive care units

3 Neonatal care units, including delivery, nursery, and neonatal intensive care unit

4 Hospital medical units

5 Transportation within the hospital and during ambulance or air ambulance transportation

6 Diagnostic testing, such as pulmonary function testing, exercise testing, and during sleep studies

7 Subacute care centers, such as nursing homes and rehabilitation centers

8 Home care patients

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Pulse oximetry, oxygen and anaesthesia:

Pre-oxygenation:

Breathing 100% oxygen prior to induction of anaesthesia (preoxygenation) increases the oxygen stores in the lungs. If a patient stops breathing and is not ventilated, the amount of oxygen in the lungs will rapidly diminish. If the patient has been given 100% oxygen to breathe for several minutes prior to induction of anaesthesia, the increased oxygen reservoir will supply much needed oxygen, adding potentially life-saving minutes. There are many situations where this may be important. One example is in the pregnant mother where the enlarged uterus reduces lung volume and the metabolic demands are increased by the foetus. Another example is in young children who have small lung volumes and high metabolic demands. They can use up oxygen very quickly and can sometimes be resistant to efforts to preoxygenate them.

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During anaesthesia, patients’ airways may become obstructed, their breathing may become depressed, their circulation may be affected by blood loss or an abnormal heart rhythm or the anaesthetic equipment may develop a problem such as an accidental disconnection or obstruction of the breathing circuit. These factors can result in a reduction of oxygen delivery to the tissues which, if not managed correctly, could lead to injury or death. The earlier the anaesthesia provider detects a problem, the sooner it can be treated so that no harm comes to the patient. During anaesthesia the oxygen saturation should always be 95 – 100%. If the oxygen saturation is 94% or lower, the patient is hypoxic and needs to be treated quickly. A saturation of less than 90% is a clinical emergency.

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It has been difficult to identify a specific reason for the decline in anaesthesia mortality over the past three decades. Improvements in monitoring, ventilator safety, and provider training all occurred during this time. Yet, most would agree that the implementation of monitoring standards was critical. These standards transformed pulse oximetry from a technology that was rarely used into an essential device in nearly every operating room in the developed world. They allowed anaesthesia providers to continuously monitor oxygenation and detect hypoxemia earlier. Anaesthesiologists no longer had to wait for clinical signs, such as cyanosis, to respond to a hypoxic patient. Consequently, technical mishaps such as circuit disconnection, airway dislodgement or obstruction, or inadequate oxygen administration were identified sooner and providers could respond before adverse events occurred. Surprisingly, the relatively rapid inclusion of pulse oximetry into the anaesthesia armamentarium occurred without level one (randomized) evidence. In fact, most of the early data were observational. One of the most influential studies, published by Cooper and colleagues in 1984, involved 139 anaesthesia provider interviews. Over 500 “incidents” and 70 “critical incidents” were discussed with investigators. From these interviews, the authors determined that the leading cause of mortality was the failure to deliver adequate amounts of oxygen. Pulse oximetry would have made a difference in many of these incidents. Since Cooper’s study, there have been at least seven randomized controlled trials on pulse oximetry. One had inadequate postoperative data, which limited its usefulness for this discussion. Of the remaining six, the study published by Moller and colleagues in 1993 was by far the largest and most informative. In this study, over 20,000 adults undergoing general or regional anaesthesia were randomized to either pulse oximetry or no pulse oximetry during surgery and in the postoperative recovery unit. The primary outcome measures were hypoxemia detection and perioperative and postoperative complications. The authors clearly state in the discussion that the study was not powered to detect differences in mortality. Nearly 2 million patients would have been needed to include mortality as an outcome. Several critical pieces of information were obtained from this trial. Of utmost importance, the rate of hypoxemia detection increased nearly 20 fold in the pulse oximetry group (p<0.0001). Endobronchial intubation and hypoventilation were also detected more frequently. Patients with pulse oximeters experienced 50% fewer myocardial ischemic events than those without pulse oximeters (p=0.03). Cardiac arrest was also less frequent with pulse oximetry, although this difference was not statistically significant (4 arrests among 9,578 patients with pulse oximetry; 11 arrests among 9,772 patients without; 1 sided p value=0.06). Clearly, pulse oximetry benefited patients. It allowed identification of inappropriate airway management by revealing hypoxemia, and it decreased the frequency of both myocardial ischemia (presumably by ensuring adequate oxygenation of the myocardium) and cardiac arrest. As expected, mortality rates were unchanged (3 deaths in oximetry group and 4 in the control) as were postoperative morbidity rates, which included respiratory, cardiovascular, neurologic and infectious complications. Of the remaining 5 randomized trials which included nearly 1,500 patients, pulse oximetry consistently allowed early detection of hypoxemia by anaesthesia providers.  None showed a mortality benefit. Although a randomized trial of two million patients addressing the effect of pulse oximetry on mortality would be powerful, this study will likely never be done; pulse oximetry is the standard of care today, and most would consider further attempts at randomization to be unethical. A 2014 Cochrane analysis of these trials concluded that the value of pulse oximetry “is questionable in relation to improved outcomes, effectiveness, and efficiency”; most anaesthesia experts around the world would disagree. Several retrospective reviews also strongly support the efficacy of pulse oximetry. One analysis of 2,000 anaesthesia-related adverse events showed a reduction in cardiac arrests when pulse oximetry was used.  Another review of 4,000 “incidents” in Australia and New Zealand revealed no cases of hypoxic brain injury from inappropriate ventilation after the introduction of pulse oximetry and capnography. Oximetry alone would have detected 82% of the relevant incidents and 60% prior to organ damage. Capnography alone would have detected 55% and 43%, respectively.

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In summary, pulse oximetry has been the standard of care in the developed world for nearly two decades. Though randomized data suggesting a mortality benefit are lacking, both expert consensus and a large volume of published data indicate that pulse oximetry is beneficial for patients. Anaesthesia providers in all settings have demonstrated a strong commitment to pulse oximetry since its inclusion into anaesthesia care. There are exceedingly few drawbacks to pulse oximetry once providers are appropriately trained. In resource limited settings, universal pulse oximetry could substantially improve the safety of anaesthesia. Today, if given the choice of one monitor, most anaesthesiologists would quickly choose the pulse oximeter over the electrocardiogram (ECG) or noninvasive blood pressure devices. However, pulse oximetry cannot reveal different types of cardiac arrhythmia and ST segment changes revealed by ECG monitor.

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Pulse oximetry vis-à-vis emergency and critical care:

First I will discuss role of pulse oximetry in emergency department (Emergency room [ER], accident and emergency [AE], emergency department [ED], casualty) and then I will discuss pulse oximetry in critical care (ICU).

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Pulse oximetry in emergency department (ED/ER/AE):

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Effect of routine emergency department triage pulse oximetry screening on medical management: 1995 study:

The study included 14,059 consecutive patients presenting to triage at a university ED. Of 1,175 patients having triage pulse oximetry values less than 95%, physicians ordered repeat pulse oximetry on 159 (13.5%), additional chest radiography on 5.4%, CBC count on 3.1%, arterial blood gases on 2.9%, spirometry on 0.9%, and ventilation-perfusion scans on 0.3%. Physicians ordered 178 new therapies on 134 patients (11.4%), including supplemental oxygen for 6.5%, antibiotics for 3.9%, and beta-agonists for 1.8%. Thirty-five patients (3.0%) initially scheduled for hospital discharge were subsequently admitted. Physicians changed or added diagnoses in 77 patients (6.6%). Providing physicians with routine triage pulse oximetry measurements resulted in significant changes in medical treatment of these patients.

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Effect of routine pulse oximetry measurements on ED triage classification: a 1998 study:

Pulse oximetry is commonly used to rapidly determine oxygen saturation and is incorporated in emergency triage as a screening for potential cardiopulmonary complications. This study examined the effect of routine pulse oximetry measurements on emergency department (ED) triage classification. Using a portable pulse oximeter, oxygen saturation of 1,235 adults presenting to a university-based, urban ED was obtained and each patient was assigned a classification of severity based on a standard 1-to-4 scale before and after the measurement. According to data obtained, a small but statistically significant group (2.8%) benefitted from the routine use of pulse oximetry in an emergency triage system and only 40% of these patients required admission or extended care. Although this group is small in number, the potential consequences of missing a hypoxic condition could be devastating for the individual patient. Since pulse oximetry is presently an inexpensive technology, it would seem to be a worthwhile screening tool for emergency triage.

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The accuracy of pulse oximetry in the emergency department: a 2000 study:

The objective of this retrospective study was to identify factors affecting the accuracy of pulse oximetry in the ED. Over a 3-year period, 664 consecutive emergency department (ED) patients had simultaneous arterial blood gas (ABG) and pulse oximeter readings taken. Pulse oximeter saturations (SpO2) were compared with ABG CO-oximeter saturations (SaO2) for accuracy. Multiple variables including age, sex, hemoglobin, bicarbonate, pH, and carboxyhemoglobin (COHb) were analyzed to see if they affected SpO2 accuracy. ROC curves were used to determine the best pulse oximeter threshold for detecting hypoxia. Using multivariate analysis, COHb was the only statistically significant factor affecting the accuracy of pulse oximetry. In patients with COHb < 2%, SpO2 overestimated SaO2 by more than 4% in 8.4% of cases. In patients with COHb ≥ 2%, SpO2 overestimated SaO2 by more than 4% in 35% of cases. The best pulse oximetry threshold for detecting hypoxia is 92%. At this threshold, if COHb is <2%, pulse oximetry has a sensitivity of 0.92 and specificity of 0.90. If COHb is ≥2%, sensitivity is 0.74 and specificity is 0.84. For patients likely to have a COHb < 2, pulse oximetry is an effective screening tool for detecting hypoxia. However, more caution must be exercised when using pulse oximetry in patients likely to have a COHb ≥ 2%.

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The accuracy of pulse oximetry in emergency department patients with severe sepsis and septic shock: a retrospective 2010 cohort study:

Sepsis results in characteristic microcirculatory derangements that could theoretically affect pulse oximeter accuracy. The cohort consisted of 88 subjects, with a mean age of 57 years (19 – 89). The mean difference (SpO2 – SaO2) was 2.75% and the standard deviation of the differences was 3.1%. Subgroup analysis demonstrated that hypoxemia (SaO2 < 90) significantly affected pulse oximeter accuracy. The mean difference was 4.9% in hypoxemic patients and 1.89% in non-hypoxemic patients (p < 0.004). In 50% (11/22) of cases in which SpO2 was in the 90-93% range the SaO2 was <90%. Though pulse oximeter accuracy was not affected by acidoisis, hyperlactatementa, anemia or vasoactive drugs, these factors worsened precision.  Pulse oximetry overestimates ABG-determined SaO2 by a mean of 2.75% in emergency department patients with severe sepsis and septic shock. This overestimation is exacerbated by the presence of hypoxemia. When SaO2 needs to be determined with a high degree of accuracy arterial blood gases are recommended.

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Pulse oximetry in critical care:

Pulse oximetry is a routine part of the monitoring and management of critically ill patients. Studies have proposed that specific pulse oximeter oxygen saturations (SpO2) be targeted to decrease the likelihood of hypoxemia, to titrate fractional inspired oxygen, and to wean mechanical ventilation. The accuracy of pulse oximetry to estimate arterial oxygen saturation (SaO2) in critically ill patients has yielded mixed results. Both the degree of inaccuracy, or bias, and its direction has been inconsistent. In addition, while certain studies of critically ill patients have demonstrated that hypoxemia, anemia, requirement for vasoactive drugs, and acidosis influence the accuracy of pulse oximetry, others have not. Data on the effects of other physiologic derangements, such as hyperlactatemia and bacteremia, are absent.  Pulse oximeters utilize the pulsatile nature of arterial blood flow to distinguish it from venous flow and estimate oxygen saturation in arterial blood. Processes that increase venous blood flow or alter pulsatility can interfere with the ability of pulse oximeters to estimate arterial oxygen saturation. Hemodynamic derangements in septic patients, such as arteriovenous shunting, cutaneous arteriolar dilation and decreased vascular resistance can alter pulsatility and venous blood flow and therefore theoretically affect pulse oximeter accuracy. When reproduced in healthy volunteers, cutaneous vasodilation has been shown to interfere with the pulse oximetry signal and significantly decrease its accuracy. This has also been demonstrated in animal models of severe sepsis.

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Because such recent oxygen therapies substitute the SpO2 for SaO2, the accuracy of pulse oximeters around 90% is crucial to avoid hypoxemia, but some studies suggest that SpO2 overestimates SaO2, especially in patients with critically illnesses. In a retrospective study including patients with septic shock, Wilson et al. reported that the mean bias (SpO2-SaO2) was positive and 2.75 +/- 3.1%. Wilson et al. also showed that among patients with 90%-93% SpO2 value, 50% of patients were with hypoxemia (SaO2< = 90%). Jubran et al.  retrospectively evaluated patients in the ICU and found that the cut-off value of SpO2 to detect hypoxemia (SaO2< = 90%) should be 94%. These results alert the possibility that SpO2 overestimates SaO2 in the ICU, and a cut-off value of SPO2< = 90% may leave patients at risk for hypoxemia. Because each pulse oximeter follows different algorithms, it is necessary to define optimal SpO2 values to avoid hypoxemia by gathering SaO2 and SpO2 data prospectively from patients in the ICU. Of note, patients in the ICU have different backgrounds and frequently have hemodynamic instability and hypoxemia. Studies have shown that these factors influence the SpO2 values. Therefore, patients with poor oxygenation and without hemodynamic instability, hypercapnia and acidosis may be ideal candidates for defining optimal SpO2 values to avoid hypoxemia.

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Accuracy of pulse oximetry in the intensive care unit: a 2001 study:

Pulse oximetry (SpO2) is a standard monitoring device in intensive care units (ICUs), currently used to guide therapeutic interventions. Few studies have evaluated the accuracy of SPO2 in critically ill patients. One hundred two consecutive patients admitted to the ICU in whom one or serial arterial blood gas analyses (ABGs) were performed and a reliable pulse oximeter signal was present. For each ABG, authors collected SaO2, SpO2, the type of pulse oximeter, the mode of ventilation and requirement for vasoactive drugs. Three hundred twenty-three data points were collected. The mean difference between SpO2 and SaO2 was -0.02% and standard deviation of the differences was 2.1%. From one sample to another, the fluctuations in SpO2 to arterial saturation difference indicated that SaO2 could not be reliably predicted from SPO2 after a single ABG. Subgroup analysis showed that the accuracy of SpO2 appeared to be influenced by the type of oximeter, the presence of hypoxemia and the requirement for vasoactive drugs. Finally, high SpO2 thresholds were necessary to detect significant hypoxemia with good sensitivity. Large SpO2 to SaO2 differences may occur in critically ill patients with poor reproducibility of SpO2. A SpO2 above 94% appears necessary to ensure a SaO2 of 90%.

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Pulse oximetry in COPD, Asthma and other respiratory illnesses:

Chronic respiratory diseases such as COPD and asthma are among the most common health conditions seen in primary care practices, affecting more than 1 billion patients worldwide. Primary care clinicians are also often the first point of contact for patients suffering from acute respiratory infections such as influenza and pneumonia. These health care professionals need tools to help them evaluate, monitor, and decide when to refer patients with respiratory conditions. In patients with COPD, pulse oximetry is useful in stable patients with severe disease (FEV1 < 50% predicted), and in patients with worsening symptoms or other signs of an acute exacerbation, as a tool for patients to use at home to assist with their management under physician guidance. It is important to note that pulse oximetry complements, rather than competes with, spirometry in the assessment of COPD patients. Spirometry remains the gold standard for diagnosing and staging COPD, while pulse oximetry provides a method for rapid assessment especially of short-term respiratory compromise. In patients with asthma, pulse oximetry complements peak flow meters in assessing the severity of asthma attacks/exacerbations and response to a treatment.

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Clinical Questions:

1. In patients with chronic obstructive pulmonary disease, is pulse oximetry effective in assessing the need for long-term oxygen therapy (LTOT), compared to arterial blood gas?

2. In patients with asthma, is oxygen saturation monitoring by pulse oximetry an objective measure of acute asthma severity compared to peak expiratory flow rate?

3. In patients with community-acquired pneumonia does pulse oximetry accurately stratify patients requiring hospital admission compared to signs and symptoms alone?

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Answers to clinical questions:

1. In terms of COPD, studies suggest that pulse oximetry is not a reliable method alone for diagnosis. COPD is currently diagnosed based on clinical features along with spirometry, where a ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) of less than 0.7 indicates airway obstruction. Oxygen saturations are not useful for diagnosis of COPD; saturations of <98% had sensitivity of 79%, but specificity of only 37%. However, pulse oximetry could have a valuable role in determining long-term oxygen therapy criteria in patients with COPD, and in indicating the need for referral to hospital in acute exacerbations.

2. The 2008 British Thoracic Society (BTS) guideline on the management of asthma and the Scottish Intercollegiate Guidelines Network recommend SpO2 monitoring by pulse oximetry as an objective measure of acute asthma severity, particularly in children, in both primary and secondary care. In children who require oxygen, pulse oximetry is recommended to determine the adequacy of oxygen therapy and the need for ABG analysis. According to these guidelines, a SpO2 <92% is considered life threatening and these patients require an ABG measurement. What is less clear is how useful SpO2 is compared to other measures of asthma severity in primary care, such as peak flow or clinical assessment.

3. Studies into the diagnosis of community acquired pneumonia (CAP) have indicated the identification of arterial hypoxaemia has direct treatment implications, including the delivery of supplemental oxygen and hospitalisation, for more intensive clinical observation. The routine use of pulse oximetry in patients suspected of having CAP would detect clinically unrecognised hypoxaemia, thereby identifying patients requiring hospitalisation.  A 2004 update of the BTS guideline for the management of CAP in adults recommended pulse oximetry, with appropriate training, should become increasingly available to GPs responsible for the assessment of patients in the out-of-hours setting, for assessment of severity and oxygen requirement for patients with CAP and other acute respiratory illnesses. The extent to which SpO2 sats provide diagnostic information that complements clinical assessment of children by GPs is not known. NICE lists SpO2 <95% as an amber flag feature in assessing children with acute febrile illness. This guideline also recommends measuring heart rate in children with acute illness. Accurate measurement of heart rate in children is difficult using non-electronic methods; however, its added value as a vital sign in children is still unclear in primary care.

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What is the normal range for pulse oximeter readings in a patient with COPD?

The patient with COPD probably lives with an O2 saturation of 88- 90(with the help of O2). His PaO2 is less than 80mm. He probably never reaches a normal O2 level. However, he has learned to live with these low values. He has adjusted to a life with less O2 and more CO2 on board. He eventually, over years, becomes exhausted and O2 sats will gradually drop in end-stage COPD. There is no set range specifically for COPD patients. However, if the patient has COPD with CO2 retention you generally want to keep SpO2 around 90-92% so you do not knock out there hypoxic drive.

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Home overnight pulse oximetry (OPO) has been used to evaluate nocturnal desaturation in patients with chronic obstructive pulmonary diseases (COPD).  However, Lewis et al (2003) found that nocturnal desaturation in patients with COPD exhibited marked night-to-night variability when measured by home OPO. A single home OPO recording may be insufficient for accurate assessment of nocturnal desaturation.  Gay (2004) stated that for COPD patients who exhibit more profound daytime hypercapnia, polysomnography is preferred over nocturnal pulse oximetry to rule out other co-existing sleep-related breathing disorders such as OSA (overlap syndrome) and obesity hypoventilation syndrome. An interesting observation was the presence of a moderate to strong correlation between the severity of airflow obstruction (FEV1 % predicted) and SpO2 in the COPD patients who presented with an acute exacerbation or worsening of dyspnoea (r = 0.55 and r = 0.31, respectively), whereas no relevant correlation was observed in the patients with stable COPD (r = 0.19). These observations suggest that with regard to primary care COPD, pulse oximetry is mainly useful in patients with (very) severe airflow obstruction (FEV1 % predicted ≤50%) and worsening of symptoms. This coincides with previous observations from a Spanish study in stable COPD patients, which showed that the rate of tests with SPO2 ≤92% increases when the FEV1 % predicted value is <50%.

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Current Clinical Uses of Pulse Oximetry in Primary Care COPD:

A. Stable disease:

• Establishing a baseline value in patients with stable disease.

• Monitoring of patients with exercise-related dyspnea.

• In patients with moderate to severe COPD, a screening tool to identify patients (i.e., those with SpO2 < 92%) who should be referred for comprehensive oxygen assessment.

• In patients with stable COPD or those recovering from an exacerbation at home, an SpO2 88% or less is a strong indication to initiate long-term oxygen therapy. However, ideally the decision to initiate oxygen therapy should be made based on arterial oxygen tension (PaO2 < 7.3 kPa / 55 mm Hg).

• Titrating oxygen flow setting in patients on long-term oxygen therapy, provided their disease is stable and they have good circulation. In general, the goal should be to maintain SpO2 > 90% during all activities.

• Evaluation of patients with severe disease (FEV1 < 50% predicted), cyanosis, or cor pulmonale for possible respiratory insufficiency/failure.

B. Exacerbations:

• Assessment of patients with acutely worsening symptoms, especially dyspnea, and determination of the severity of the exacerbation.

• Triage for arterial blood gas measurement, referral to emergency department, and/or determination of whether to initiate oxygen therapy or other treatment for exacerbation.

• Monitoring patients after the initiation of oxygen therapy. Measure SpO2 regularly—every 5 to 30 minutes, especially if the patient’s clinical condition deteriorates. For patients at risk of hypercapnic respiratory failure, aim to maintain SpO2 88-92%; for all other patients, aim for SpO2 94-98%.

• Evaluating patients for initiation of hospital-at-home/intermediate care, and monitoring them once they are enrolled in this form of care.

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The benefits of long-term oxygen therapy (LTOT) in patients with chronic obstructive pulmonary disease (COPD) have been reported by a number of investigators. Since the 1980s, domiciliary oxygen therapy has been generally accepted as an important part of the routine treatment of COPD patients with chronic severe hypoxaemia. The main indication for LTOT is a low arterial oxygen tension (PaO2), usually lower than 55 mmHg (7.3 kPa). The prescribed oxygen flow should increase PaO2 to at least 65 mmHg (8.7 kPa). The blood gas tensions used to qualify the patients for treatment are measured at rest. The oxygen flow rate is also adjusted in resting conditions. In some cases, arterial oxygen saturation (SaO2) during treadmill/cycle ergometer exercise or during sleep is also assessed, but rather to confirm the subject’s eligibility for LTOT than to establish the adequate oxygen flow rate. After the prescription of LTOT, the patients are followed in out-patient clinics or at home, and blood gas measurements are periodically performed at rest. Thus, there is no information about SaO2 in those patients during their daily activities at home. It is possible that some activities may cause important drops in SaO2, despite adequate oxygenation while resting 24 h.

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How accurate are pulse oximeters in patients with acute exacerbations of chronic obstructive airways disease? A 2001 study:

In conclusion, there is not sufficient agreement for oxygen saturation measured by pulse oximetry to replace analysis of an arterial blood gas sample in the clinical evaluation of oxygenation in emergency patients with COPD. However, oxygen saturation by pulse oximetry may be an effective screening test for systemic hypoxia, with the screening cut-off of 92% having sensitivity for the detection of systemic hypoxia of 100% with specificity of 86%.

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Ambulatory pulse oximetry monitoring in Japanese COPD outpatients not receiving oxygen therapy: a 2014 study:

This study aims to analyse the frequency of desaturation in COPD outpatients, and investigate whether the desaturation profile predicts the risk of exacerbation. The 24-hour ambulatory oximetry monitoring provided precise data regarding the desaturation profiles of COPD outpatients. Both daytime and night-time desaturations were infrequent. The proportion of ambulatory SpO2 values below 90% was not a significant predictor of exacerbation.

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Six-Minutes Walk test:

Doctors often use an assessment called the six-minute walk test for patients with heart and lung disease, such as congestive heart failure (CHF), chronic obstructive pulmonary disease (COPD) and asthma. The test provides information regarding a patient’s functional capacity and response to therapy for a wide range of chronic cardiopulmonary conditions.

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Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and disability worldwide, and is predicted to become the third highest cause of death by 2020. Desaturation profiles during a 6-minute walk test (6MWT) may predict prognosis primarily in patients with severe COPD with a percent predicted forced expiratory volume in one second (FEV1) of <50%. Time to desaturation during a 6MWT also predicts desaturation time in 24-hour ambulatory oximetry monitoring primarily in moderately hypoxaemic COPD patients with a resting partial pressure of arterial oxygen (PaO2) between 60 and 70 mmHg. However, it remains unknown whether desaturation profiles measured by ambulatory oximetry can predict prognosis in COPD patients. Transient desaturations have been observed in patients with moderate to severe chronic pulmonary disorders, even without significant resting hypoxemia. Point measurements of resting oxygen saturation by pulse oximetry (SpO2) and PaO2, the conventional parameters used to determine requirements of long-term oxygen therapy, are not sufficient for assessment of desaturation during activities of daily living. Field walking tests such as the 6MWT, which is the standard test used for assessment of functional exercise tolerance, do not always provide a good reflection of variations in oxygen saturation, because most activities of daily living are performed at submaximal levels of effort. 6MWT results did not predict the degree of desaturation during defecation in patients with chronic respiratory failure. Conventional assessment methods are therefore not satisfactory for obtaining a comprehensive understanding of oxygen saturation throughout the day.

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Oxygen desaturation during a 6 min walk test is a sign of nocturnal hypoxemia: a 2011 study:

Patients with chronic obstructive pulmonary disease (COPD) may experience sleep disordered breathing with nocturnal desaturation.  Results from the present study suggest that monitoring oxygen saturation changes during a 6MWT is useful in helping to identify COPD patients who may experience significant nocturnal desaturation.

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Asthma:

Clinical findings are usually insufficient to properly determine the severity of acute asthma. Significant changes in lung function may be present despite the lack of clinical manifestation, as first reported in the 1970′s and confirmed by subsequent studies. The severity of acute asthma is classified as mild, moderate, severe, and very severe based on clinical and functional criteria, the most widely used being pulse oximetry (SpO2) and peak expiratory flow (PEF). Few reports are available about possible correlations between these two methods in children and adolescents. Although the Global Initiative for Asthma (GINA) states that measurements of lung function and oximetry are critical for patient assessment, it is not clear whether both methods should be included in the evaluation of acute asthma, since no critical comparison of the two measurements has been done.

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Use of pulse oximetry in the hospital management of acute asthma in childhood: a 1993 study:

A post-nebulizer saturation of less than 91 % had a sensitivity of 100% [95% confidence interval (CI), (54–1001 with a specificity of 98%] (95% CI, 92–100) and a positive predictive value of 86% for severe asthma necessitating intravenous treatment.

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Pulse oximetry in the evaluation of the severity of acute asthma and/or wheezing in children: a 1999 study:

SpO2 levels correlated positively with FEV1 and FVC (25-75) values, and negatively with clinical scores and heart rate. The data revealed that a clinical score greater than 3 and an SpO2 < 94% were associated with increased severity of the asthma attack. In addition, SpO2 levels < or = 92% were associated with a 6.3-fold greater relative risk for requiring additional treatment. Authors concluded that determination of oxygen saturation by pulse oximetry is helpful in monitoring the severity of an acute exacerbation of asthma and/or wheezing, and has a prognostic value.

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Correlations between pulse oximetry and peak expiratory flow in acute asthma: a 2007 study:

The present prospective observational study was carried out to determine if there is correlation between pulse oximetry and peak expiratory flow determination in 196 patients with acute asthma aged 4 to 15 years diagnosed according to the Global Initiative for Asthma criteria. The results showed that one measure cannot substitute the other (Pearson’s coefficient <0.7), probably because they evaluate different aspects in the airways, suggesting that peak expiratory flow should not be used alone in the assessment of acute asthma in children and adolescents.

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Role of pulse oximetry during an asthma attack:

• Evaluation and assessment of severity, complementing peak flow meter data.

• Triage for arterial blood gas measurement, referral to emergency department, and/or determining when to initiate acute oxygen therapy.

• Monitoring patients after the initiation of oxygen therapy or response to other therapy

• Particularly important in children with severe acute wheezing.

• Follow-up of patients after a severe or complicated exacerbation.

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A National Heart, Lung and Blood Institute/World Health Organization Global Asthma Initiative Report concluded that pulse oximetry was not an appropriate method of monitoring patients with asthma.  The report explained that, during asthma exacerbations, the degree of hypoxemia may not accurately reflect the underlying degree of ventilation-perfusion (V-Q) mismatch.

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Foetal and paediatric pulse oximetry:

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Foetal Pulse Oximetry:

There is a new intervention in maternity care. And it may very well reduce some the need for some caesarean sections due to unreliable FHR tracings. It is the Fetal Pulse Oximetry. Introduced in the 1990s and approved by the FDA in 2000, this technology is based on the same principle as adult pulse oximetry, which has become common-place in hospitals world-wide. Fetal oximetry is a developing technique that uses reflectance oximetry, using LEDs of 735nm and 900nm. The fetal oxygen monitor has a single-use, disposable sterile sensor which is inserted through the birth canal once the membranes have ruptured, the cervix is < 2 cm, fetus is at -2 station or below, and gestational age is at least 36 weeks. The sensor rests against the fetal cheek, forehead or temple and is held in place by the uterus. The oxygen saturation is displayed on the monitor screen as a percentage. The normal oxygen saturation for a baby in the womb, receiving oxygenated blood from the placenta, is usually between 30 and 70 percent. Varney cautions that when the fetal oxygen saturation remains less than 30% or the signal is unobtainable for more than 10 minutes, the need for intervention is present. However, some conditions may alter readings including fetal scalp edema, caput succedaneum, dark/thick/curly hair, or vernix. There has been some interest in the use of fetal pulse oximetry in combination with routine cardiotocography (CTG) monitoring, although its use does not reduce the operative delivery rate. Contraindications to fetal oxygen monitoring include placenta previa, a FHR pattern that clearly indicates immediate delivery, other reasons for immediate delivery such as profuse vaginal bleeding, maternal HIV, active genital herpes or Hepatitis B infections.

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Paediatric pulse oximetry:

Accuracy of pulse oximetry in neonates, infants and children:

Pulse oximetry equipment is largely calibrated using adult patients. Various studies represent a comprehensive attempt to gain information on the accuracy of pulse oximetry devices in infants and children across a large range of oxygen saturations, child ages, and skin colors. The gold standard with which the instruments were compared was arterial oxygenation readings obtained by arterial blood gas measurements.

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Normal oxygen saturation values in paediatric patients: a 2005 study.

Although SpO2 of 95% and 96% are adequate (i.e., not requiring acute oxygen therapy), these values are associated with higher rates of respiratory and cardiovascular illnesses and thus should be considered potentially abnormal. SpO2 of 97% is on the border of normal. Normal SpO2 can occur with respiratory and cardiovascular illnesses, but SpO2 less than 97% is associated with a higher risk of respiratory and cardiovascular illnesses.

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Validation of oxygen saturation monitoring in neonates: a 2007 study.

The mean difference of oxygen saturation as determined by pulse oximetry and oxyhemoglobin in arterial blood samples was 2.5%. The safety limits for pulse oximeters are higher and narrower in neonates than in adults, and clinical guidelines for neonates may require modification.

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Pulse oximeter accuracy and precision affected by sensor location in cyanotic children: a 2008 study.

Children’s digits are often too small for proper attachment of oximeter sensors, necessitating sensor placement on the sole of the foot or palm of the hand. No study has determined what effect these sensor locations have on the accuracy and precision of this technology. The objective of this study was to assess the effect of sensor location on pulse oximeter accuracy (i.e., bias) and precision in critically ill children. Co-oximeter-measured arterial oxygen saturation (SaO2) was compared with simultaneously obtained pulse oximetry saturations (SpO2). A total of 98 measurements were obtained, 48 measurements in the upper extremities (finger and palm) and 50 measurements in the lower extremities (toe and sole). The median Sao2 was 92% (66% to 100%). There was a significant difference in bias (i.e., average SpO2 – Sao2) and precision (+/-1 sd) when the sole and toe were compared (sole, 2.9 +/- 3.9 vs. toe, 1.6 +/- 2.2, p = .02) but no significant difference in bias and precision between the palm and the finger (palm, 1.4 +/- 3.2 vs. finger, 1.2 +/- 2.3, p = .99). There was a significant difference in bias +/- precision when the Sao2 was <90% compared with when Sao2 was >or=90% in the sole (6.0 +/- 5.7 vs. 1.8 +/- 2.1, p = .002) and palm (4.5 +/- 4.5 vs. 0.7 +/- 2.4, p = .006) but no significant difference in the finger (1.8 +/- 3.8 vs. 1.1 +/- 1.8, p = .95) or toe (1.9 +/- 2.9 vs. 1.6 +/- 1.9, p = .65). The Philips M1020A pulse oximeter and Nellcor MAX-N sensors were less accurate and precise when used on the sole of the foot or palm of the hand of a child with an SaO2 <90%.

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Pulse oximeter accuracy and precision at five different sensor locations in infants and children with cyanotic heart disease: a 2010 study:

Cyanotic heart disease patients pose a unique dilemma in terms of the reliability and precision of the pulse oximetry readings and the determination of the best location of the sensor, especially in infants. An understanding of the bias and precision of the pulse oximetry at various sensor sites would go a long way in the effective management of patients with cyanotic heart disease in the perioperative period. Authors strongly recommend that clinicians should verify the measurements by a co-oximeter and evaluate the pulse oximetry sensor used with the particular body site reliability indices to avoid any unacceptable over- or underestimation of the SaO2. This becomes even more relevant in hypoxemic patients with low SaO2 readings as the margin of safety is very small. Authors found that sole is the most accurate site of sensor location in cyanotic heart disease paediatric patients. Authors could also re-establish the finding that at low saturation states, pulse oximetry accuracy deteriorates and tends to overestimate the SaO2. In terms of reproducibility, the best sensor site could not be determined definitely and consistently in our study.

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Accuracy of Pulse Oximetry in Children: a 2013 study:

The study objective was to measure the accuracy of pulse oximetry in the saturations from pulse oximetry (SpO2) range of 65% to 97%.  This institutional review board–approved prospective, multicenter observational study in 5 PICUs included 225 mechanically ventilated children with an arterial catheter. With each arterial blood gas sample, SpO2 from pulse oximetry and arterial oxygen saturations from Co-oximetry (SaO2) were simultaneously obtained if the SpO2 was ≤97%.  The lowest SPO2 obtained in the study was 65%. In the range of SpO2 65% to 97%, 1980 simultaneous values for SpO2 and SaO2 were obtained. The bias (SpO2 – SaO2) varied through the range of SpO2 values. The bias was greatest in the SpO2 range 81% to 85% (336 samples, median 6%, mean 6.6%, accuracy root mean squared 9.1%). SpO2 measurements were close to SaO2 in the SpO2 range 91% to 97% (901 samples, median 1%, mean 1.5%, accuracy root mean squared 4.2%). This study identified that the accuracy of pulse oximetry varies significantly as a function of the SpO2 range. Saturations measured by pulse oximetry on average overestimate SaO2 from Co-oximetry in the SpO2 range of 76% to 90%. Better pulse oximetry algorithms are needed for accurate assessment of children with saturations in the hypoxemic range.

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Congenital heart disease (CHD):

Cardiovascular malformations are the commonest type of congenital malformation, but a sizeable proportion is not detected by routine neonatal examination.  Cardiovascular malformations account for 6-10% of all infant deaths and 20-40% of deaths caused by congenital malformation. About 1-1.8 babies per 1000 live births have a duct dependent circulation, with a persistent ductus arteriosus being necessary for survival. These babies are at particular risk from the worldwide trend towards early discharge from maternity units, as the effects of ductal closure may not be apparent at an early discharge examination. Some 10-30% of babies who die from congenital heart disease do not have their condition diagnosed before autopsy. In Sweden over the past decade increasing proportions of babies with critical congenital heart disease have been leaving hospital with their condition undiagnosed. Screening infants with non-invasive measurement of oxygen saturation has been proposed as an aid for early detection of duct dependent circulation. Current routine screening for CHDs relies on a mid-trimester anomaly ultrasound scan in pregnant women, involving imaging of the heart chambers, and a postnatal clinical examination involving assessment of the cardiovascular system. Both of these have a relatively low detection rate and a number of babies are discharged from hospital before a CHD is diagnosed.

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Routine neonatal examination fails to diagnose more than half of babies with heart disease; examination at 6 weeks misses one-third. Spending more time on physical examination is unrewarding as only milder cases of pulmonic stenosis and other relatively benign forms of CHD are diagnosed, which has little impact on the morbidity and mortality from undiagnosed CHD. Pulse oximetry can pick up lesions producing low oxygen saturation levels consequent to substantial abnormal mixing of systemic and pulmonary blood streams or critical obstructive duct-dependent lesions (mostly cyanotic CHD). Although it may fail to detect acyanotic CHD and critical CHD with non-critical obstruction or mixing, these lesions do not contribute to early mortality and morbidity.  A recent systematic review of data from 229421 new born babies reported that pulse oximetry is having high specificity and acceptable sensitivity for detection of critical CHD. The false-positive rate for detection of critical congenital heart defects was particularly low when new born pulse oximetry was done after 24 h from birth than when it was done before 24 h. Although pulse oximetry is inexpensive and without side effects, it cannot detect CHD in every neonate with congenital heart disease, before they leave the hospital. Pulse oximetry is highly specific for detection of critical congenital heart defects with moderate sensitivity that meets criteria for universal screening. In a country with a huge population and poor prenatal diagnostic infrastructure, it is probably the best thing to do and should become a recommendation.

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Critical Congenital Heart Disease (CCHD):

According to the Centers for Disease Control and Prevention (CDC), congenital heart defects account for 24% of infant deaths due to birth defects. In the United States, about 4,800 (or 11.6 per 10,000) babies born every year have CCHDs. Babies with a CCHD are at significant risk for death or disability if their CCHD is not diagnosed and treated soon after birth. Pulse oximetry, which is a test to determine the amount of oxygen in the blood, is the recommended screening method to detect CCHDs in newborns.

There are seven defects classified as CCHD:

• Hypoplastic left heart syndrome

• Pulmonary atresia (with intact septum)

• Tetralogy of Fallot

• Total anomalous pulmonary venous return

• Transposition of the great arteries

• Tricuspid atresia

• Truncus arteriosus

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Gold standard:

Postnatal echocardiography is well established as the gold standard for diagnosing CHDs. However, it has to be remembered that, as studies of prevalence show, echocardiography may also contribute to an apparent rising incidence of CHDs mainly as a result of the detection of abnormalities which are of no functional or clinical significance. As a result, echocardiography is likely to have significant limitations as a screening tool, mainly because of the high false positive rate, but also as a result of cost and lack of availability of trained personnel to perform the examinations

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Pulse oximetry:

The rationale for pulse oximetry screening is based on the fact that hypoxaemia is present, to some degree, in the majority of CHDs. This may result in obvious cyanosis; however, mild degrees of hypoxaemia cannot be detected by clinical observation, even by experienced clinicians. The difficulty is exacerbated in infants with pigmented skin.

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A common feature of many forms of congenital heart disease is hypoxemia. Hypoxemia results from the mixing of systemic and venous circulations or parallel circulations as one might see in dextro-transposition of the great arteries. Hypoxemia may result in obvious cyanosis. However, generally, 4 to 5 g of deoxygenated hemoglobin is needed to produce visible central cyanosis, independent of hemoglobin concentration. For the typical newborn with a hemoglobin concentration of 20 g/dL, cyanosis will only be visible when arterial oxygen saturation is <80%; if the infant only has a hemoglobin concentration of 10 g/dL, the saturation must be <60% before cyanosis is apparent. Importantly, those children with mild hypoxemia, with arterial oxygen saturation of 80% to 95%, will not have visible cyanosis. Moreover, the identification of cyanosis is particularly problematic in black and Hispanic neonates because of skin pigmentation.

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Pulse Oximetry Screening of Newborns:

In the fall of 2011, universal pulse oximetry screening of newborns was recommended by Secretary Kathleen Sebelius of the Department of Health and Human Services, the American Academy of Paediatrics, the American College of Cardiology and the American Heart Association. The objective is to prevent morbidity and mortality associated with unrecognized critical congenital heart disease. The guideline recommends screening of all newborns in the well-baby or intermediate-care nursery between 24 and 48 hours of age, or as close as possible to discharge if the newborn is discharged prior to 24 hours of age. False positives increase when screening is performed before 24 hours of age or when the newborn is asleep. Currently, CCHD is not detected in some newborns until after their hospital discharge, which results in significant morbidity and occasional mortality. Furthermore, routine pulse oximetry performed on asymptomatic newborns after 24 hours of life, but before hospital discharge, may detect CCHD. Routine pulse oximetry performed after 24 hours in hospitals that have on-site paediatric cardiovascular services incurs very low cost and risk of harm.

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How should failed screens be handled?

Failed screens should be resolved prior to discharge by echocardiography; discussion with a pediatric cardiologist prior to obtaining an echocardiogram is strongly recommended.

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What is the sensitivity of the screen?

An estimated 1/500 to 1/1,000 newborns will fail the screen; 20% to 25% of those that fail will have critical congenital heart disease. The screen has a sensitivity of 60% to 75% for critical congenital heart disease, and thus a normal screen does not rule out heart disease.

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When should babies be screened?

Many normal newborns have oxygen saturations lower than 95 to 100 percent in the first hours of life as their bodies adjust to life outside the womb. By 24 hours of life this transition period should be done and oxygen saturations should be 95 percent or greater. Pulse oximetry screening should always be done after 24 hours to avoid falsely labelling a baby as failing the screening test. Some babies require supplemental oxygen after they are born. In this case, screening should be delayed until the baby no longer needs extra oxygen. If a baby is going home on supplemental oxygen, pulse oximetry screening for CCHD should be done prior to discharge.

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Where should babies be screened?

A pulse oximetry probe will measure the oxygen saturation in the right hand and in either of the feet. Measuring in these two places gives a more accurate picture of the function of the heart. Right upper extremity probe attachment is pre-ductal location giving more accurate result.

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How are babies screened?

“Two Sites, Three Strikes” is the easiest way to understand CCHD screening:

Two Sites- A pulse oximetry probe will measure the oxygen saturation in the right hand and the right or left foot. Measuring in these two places gives a more accurate picture of the function of the heart.

Three Strikes -A baby has three chances to pass pulse oximetry screening unless they are found to have very low oxygen saturation (less than 90 percent) in the hand or the foot at any point in the screening process.

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How does a baby pass or fail the screen?

Pass- Pulse oximetry reading greater than 95 percent in either hand or foot and difference between hand and foot less than or equal to 3 percent is an immediate pass and no further testing is needed.

Fail- Pulse oximetry reading less than 90 percent anywhere anytime is an immediate fail and baby requires further evaluation. Learn more about a failed screening.  Repeat if the pulse oximetry reading is between 90 and 94 percent in right hand and foot or if there is greater than 3 percent difference between two sites, the screen will be repeated one hour later. At the repeat screen the baby can pass, fail, or require one more repeat screen an hour later. After the third screen the baby must either pass or fail. Pulse oximetry between 90 and 94 percent in right hand and foot or greater than 3 percent difference between two sites on the third screen is considered a fail.

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Accuracy of pulse oximetry in screening for congenital heart disease in asymptomatic newborns: a systematic review of 2007.

Eight studies were included with a total of 35960 newborns. Pulse oximetry was performed on asymptomatic newborns in all studies; three studies excluding newborns with an antenatal diagnosis of congenital heart disease. Either functional or fractional oxygen saturation was measured by pulse oximetry with oxygen saturation below 95% as the cut‐off level in most studies. On the basis of the eight studies, the summary estimates of sensitivity and specificity were 63% (95% CI 39% to 83%) and 99.8% (95% CI 99% to 100%), respectively, yielding a false positive rate of 0.2% (95% CI 0% to 1%). Pulse oximetry was found to be highly specific tool with very low false positive rates to detect congenital heart disease. Large, well‐conducted prospective studies are needed to assess its sensitivity with higher precision.

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Impact of pulse oximetry screening on the detection of duct dependent congenital heart disease: a Swedish prospective screening study in 39821 newborns: a 2009 study.

Introducing pulse oximetry screening before discharge improved total detection rate of duct dependent circulation to 92%. Such screening seems cost neutral in the short term, but the probable prevention of neurological morbidity and reduced need for preoperative neonatal intensive care suggest that such screening will be cost effective long term.

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Pulse oximetry as a screening test for congenital heart defects in newborn infants: a 2012 study.

Fifty-three of the 20,055 babies screened had a major CHD (24 critical and 29 serious), a prevalence of 2.6 per 1000 live births. Pulse oximetry had a sensitivity of 75.0% [95% confidence interval (CI) 53.3% to 90.2%] for critical cases and 49.1% (95% CI 35.1% to 63.2%) for all major CHDs. Pulse oximetry is a simple, safe, feasible test that is acceptable to parents and staff and adds value to existing screening. It is likely to identify cases of critical CHDs that would otherwise go undetected. It is also likely to be cost-effective given current acceptable thresholds. The detection of other pathologies, such as significant CHDs and respiratory and infective illnesses, is an additional advantage. Other pulse oximetry techniques, such as perfusion index, may enhance detection of aortic obstructive lesions.

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Pulse oximetry with clinical assessment to screen for congenital heart disease in neonates in China: a prospective study of 2014:

Several pioneering studies have provided evidence for the introduction of universal pulse oximetry screening for critical congenital heart disease. However, whether the benefits of screening reported in studies from high-income countries would translate with similar success to low-income countries is unknown. Authors assessed the feasibility and reliability of pulse oximetry plus clinical assessment for detection of major congenital heart disease, especially critical congenital heart disease, in China. In the pilot study, 6785 consecutive newborn babies were screened; 46 of 49 (94%) cases of asymptomatic major congenital heart disease and eight of eight (100%) cases of asymptomatic critical disease were detected by pulse oximetry and clinical assessment. In the prospective multicentre study, we screened 122738 consecutive newborn babies (120707 asymptomatic and 2031 symptomatic), and detected congenital heart disease in 1071 (157 critical and 330 major). In asymptomatic newborn babies, the sensitivity of pulse oximetry plus clinical assessment was 93·2% (95% CI 87·9–96·2) for critical congenital heart disease and 90·2% (86·4–93·0) for major disease. The addition of pulse oximetry to clinical assessment improved sensitivity for detection of critical congenital heart disease from 77·4% (95% CI 70·0–83·4) to 93·2% (87·9–96·2). The false-positive rate for detection of critical disease was 2·7% (3298 of 120 392) for clinical assessment alone and 0·3% (394 of 120 561) for pulse oximetry alone. Pulse oximetry plus clinical assessment is feasible and reliable for the detection of major congenital heart disease in newborn babies in China. This simple and accurate combined method should be used in maternity hospitals to screen for congenital heart disease.

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Use signal extraction technology for neonatal pulse oximetry:

The CCHD workgroup cited the results of two large, prospective studies of 59,876 subjects that exclusively used signal extraction technology to increase the identification of CCHD with minimal false positives. The CCHD workgroup recommended newborn screening be performed with motion tolerant pulse oximetry that has also been validated in low perfusion conditions. In 2014, a third large study of 122,738 newborns (discussed above) that also exclusively used signal extraction technology showed similar, positive results as the first two large studies.

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Limitations to newborn pulse oximetry in detection of CCHD:

There are technical limitations to oximetry measurement in the newborn. As discussed earlier, the mean SpO2 in the newborn at >24 hours of age is 97% to 98%; however, when continuous pulse oximetry is used, multiple investigators have demonstrated periodic and/or sustained desaturation below 95% during sleep, feeding, and crying.  Sustained rather than variable hypoxemia is consistent with the diagnosis of cyanotic congenital heart disease. Low oximetry readings in the setting of normal arterial oxygen saturation have been reported by multiple investigators. In fact, falsely low oximetry readings in the newborn population are known to be associated with low peripheral perfusion and motion artifact, probe placement site and partial probe detachment, and hyperbilirubinemia or dyshemoglobinemias. It is known that technical differences between the various types of oximeters in general use include measurement of functional or fractional oxygen saturation, preset signal-averaging times, and methods for the exclusion of motion artifact. There has been some research into the variability among various commercially available pulse oximeters; however, most of the variability occurs in the cyanotic range (<90%) or at the highest saturations (99% to 100%). The peak performance of the commercially available oximeters occurs in the range of 92% to 97%. Therefore, in the critical range for oximetry screening (94% to 97%), the variability of the most commonly used oximeters should be negligible.  There has also been concern that pulse oximeters may not be as accurate in darkly pigmented adults and children. At low SpO2 levels (<70%), commercially available oximeters appear to overestimate arterial saturation by 3% in darkly pigmented subjects. However, when SpO2 is >90%, measurement bias related to skin pigmentation appears negligible (<0.2%). Lastly, the quality of oximetry measurements may be lower when performed in a screening setting.

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Disease-Specific Applications of pulse oximetry in paediatric practice:

Respiratory Applications:

In paediatric practice, pulse oximetry must be readily available in any situation associated with hypoxemia. Oxygen saturation is a particularly sensitive indicator of disease severity in conditions associated with ventilation/perfusion (V/Q) mismatch, such as exacerbations of asthma or chronic lung disease of prematurity, acute bronchiolitis, and pneumonia. Conversely, SpO2 is not a reliable indicator of disease severity in proximal (laryngeal or tracheal) airway obstruction such as acute laryngotracheitis, foreign-body aspiration, and vocal cord dysfunction. The principle mechanism of hypoxemia in such cases is hypoventilation, which primarily leads to an increase in PaCO2. These patients might not present with particularly low SpO2 readings. Current guidelines state that oxygen saturation should be monitored by pulse oximetry during asthma exacerbations to assess severity of the disease and response to treatment. Mild asthma exacerbations are associated with SpO2 values of >95%, moderate exacerbations with values of 90% to 95%, and severe exacerbations with values of <90%. Although SpO2 values of <92% at presentation have been suggested to predict hospitalization or return to the hospital, more recent studies have not confirmed this finding.  Instead, a 1-hour post-treatment SpO2 of <92% to 94% has been shown to be a better predictor of the need for hospitalization. To date, there is no consensus on the SpO2 thresholds that should be used to admit, treat, and discharge infants with acute bronchiolitis. The American Academy of Paediatrics guideline recommends administration of supplemental oxygen if SPO2 values fall to <90. Pulse oximetry is essential for prompt detection and management of pediatric pneumonia, because infants and children might not appear cyanotic despite significant hypoxemia. The British Thoracic Society guideline for the management of community-acquired pneumonia recommends that symptomatic infants and children with an SpO2 of ≤92% should be treated with oxygen and admitted to the hospital.

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Cardiovascular Applications:

Pulse oximetry can be used for heart rate monitoring or might serve more specialized applications, such as the assessment of peripheral perfusion and hemodynamic status. The plethysmographic waveform has been shown to be useful in the estimation of blood pressure when manometry fails. It can also offer a semi-quantitative evaluation of “pulsus paradoxus” by identifying an exaggerated decrease of pulse-wave amplitude during inspiration.

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Neonatal Resuscitation:

Assessment of skin color is not a reliable indicator of oxygenation status during the immediate postnatal period. Moreover, the optimal management of oxygenation during neonatal resuscitation is critical, because there is strong evidence that both hypoxia and hyperoxia can be harmful. The feasibility and reliability of pulse oximetry during neonatal resuscitation have been proven in several studies. Thus, SpO2 monitoring in the delivery room is currently recommended for neonates with persistent cyanosis, when assisted ventilation and supplementary oxygen administration are required, or when neonatal resuscitation is anticipated (high-risk deliveries). Under acceptable conditions of peripheral perfusion, SpO2 values can be reliably measured ∼2 minutes after birth.  Use of new-generation devices and sensors of appropriate size, as well as probe attachment to a preductal location (i.e., right upper extremity), preferably before connecting the probe to the device, might result in more accurate and timely readings. However, health care professionals should be aware that, even in uncompromised neonates, an increase in SpO2 at levels of >90% might take >10 minutes to achieve. Therefore, pulse oximetry should be used in conjunction with, but not as a substitute for, clinical assessment during the transitional period after birth.

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Neonatal Screening for Congenital Heart Disease—already discussed vide supra:

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Prevention of Hyperoxia:

Although for ventilator-dependent patients pulse oximetry can assist in the titration of inspired oxygen concentration, it cannot reliably prevent hyperoxic events. SpO2 values of >92% do not accurately correlate with PaO2, as is clearly depicted by the shape of the Oxygen dissociation curve. At such high SpO2 values, small variations of SpO2 might relate to disproportionally wider variations of PaO2. Therefore, caution is required when interpreting pulse-oximetry readings in situations in which hyperoxia is to be avoided, especially in case of preterm and low birth weight neonates for whom excessive oxygen administration can be particularly harmful.  Although a single best range has not been established yet, there is convincing evidence that SpO2 values between 85% and 93% are sufficient to maintain normoxemia and to decrease the incidence of retinopathy of prematurity in infants receiving supplemental oxygen. In extremely preterm neonates, however, lower SpO2 targets (i.e., 85%–89%) have been associated with an increased risk of mortality compared with higher SpO2 levels (i.e., 91%–95%). To limit oxygen toxicity in premature neonates, supplemental oxygen can be tapered to maintain an oxygen saturation of 90% – thus avoiding the damage to the lungs and retinas of neonates. Although pulse oximeters are calibrated for adult haemoglobin, HbA, the absorption spectra of HbA and HbF are almost identical over the range used in pulse oximetry, so the technique remains reliable in neonates.

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Can we replace Arterial Blood Gas Analysis by Pulse Oximetry in Neonates with Respiratory Distress Syndrome: a 2015 study:

Neonates with respiratory distress syndrome (RDS) require arterial blood gas (ABG) analysis to decide on appropriate management. Authors conducted this study to investigate the validity of pulse oximetry instead of frequent ABG analysis in the evaluation of these patients. From a total of 193 blood samples obtained from 30 neonates <1500 grams with RDS, 7.2% were found to have one or more of the followings: acidosis, hypercapnia, or hypoxemia. Authors found that pulse oximetry in the detection of hyperoxemia had a good validity to appropriately manage patients without blood gas analysis. However, the validity of pulse oximetry was not good enough to detect acidosis, hypercapnia, and hypoxemia.

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Other uses of pulse oximetry:

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Blood volume and blood pressure estimation:

Photoplethysmography:

A photoplethysmogram (PPG) is an optically obtained plethysmogram, a volumetric measurement of an organ. A PPG is often obtained by using a pulse oximeter which illuminates the skin and measures changes in light absorption. A conventional pulse oximeter monitors the perfusion of blood to the dermis and subcutaneous tissue of the skin. With each cardiac cycle the heart pumps blood to the periphery. Even though this pressure pulse is somewhat damped by the time it reaches the skin, it is enough to distend the arteries and arterioles in the subcutaneous tissue. If the pulse oximeter is attached without compressing the skin, a pressure pulse can also be seen from the venous plexus, as a small secondary peak. The change in volume caused by the pressure pulse is detected by illuminating the skin with the light from a light-emitting diode (LED) and then measuring the amount of light either transmitted or reflected to a photodiode. Each cardiac cycle appears as a peak. Because blood flow to the skin can be modulated by multiple other physiological systems, the PPG can also be used to monitor breathing, hypovolemia, and other circulatory conditions. While pulse oximeters are a commonly used medical device, the PPG derived from them is rarely displayed, and is nominally only processed to determine heart rate. PPGs can be obtained from transmissive absorption (as at the fingertip) or reflection (as on the forehead). In outpatient settings, pulse oximeters are commonly worn on the finger. However, in cases of shock, hypothermia, etc. blood flow to the periphery can be reduced, resulting in a PPG without a discernible cardiac pulse. In this case, a PPG can be obtained from a pulse oximeter on the head, with the most common sites being the ear, nasal septum, and forehead. PPGs can also be obtained from the vagina and esophagus.

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PPG tracing:

Premature Ventricular Contraction (PVC) can be seen in the PPG just as in the ECG and the Blood Pressure (BP).

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Because the skin is so richly perfused, it is relatively easy to detect the pulsatile component of the cardiac cycle. The DC component of the signal is attributable to the bulk absorption of the skin tissue, while the AC component is directly attributable to variation in blood volume in the skin caused by the pressure pulse of the cardiac cycle. The height of AC component of the photoplethysmogram is proportional to the pulse pressure, the difference between the systolic and diastolic pressure in the arteries. Shamir, Eidelman, et al. studied the interaction between inspiration and removal of 10% of a patient’s blood volume for blood banking before surgery. They found that blood loss could be detected both from the photoplethysmogram from a pulse oximeter and an arterial catheter. Patients showed a decrease in the cardiac pulse amplitude caused by reduced cardiac preload during exhalation when the heart is being compressed.

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Use of Pulse Oximetry as a Noninvasive Indicator of Intravascular Volume Status: a 2013 study.

The use of pulse oximetery as a noninvasive method to assess intravascular volume status is described. Pulse oximeters providing a continuous display of the pulse waveform offer a new method of estimating relative volume status during positive-pressure ventilation. Like intraarterial pressure tracings, the peaks of the pulse waveform demonstrate increased variation in response to positive-pressure ventilation when a patient becomes hypovolemic. Pulse oximeter waveform tracings were compared with central venous pressure and intraarterial pressure tracings in 12 patients undergoing major operative procedures. A significant correlation (r = 0.61) was seen between pulse waveform variation and systolic pressure variation, which has previously been shown to be a sensitive indicator of hypovolemia. When data from individual patients were analyzed separately, the correlation between pulse waveform variation and systolic pressure variation was as high as 0.88.

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Blood pressure measurement by pulse oximetry:

Recently, another method of measuring blood pressure non-invasively, using the pulse oximeter, has been reported. This requires a manual blood pressure cuff to be placed on the same extremity as the pulse oximeter probe. The pressure is recorded at disappearance and/or reappearance of the oximeter waveform display during cuff inflation/deflation, which approximates to systolic blood pressure. This was first described in 1987 after it was noted intraoperatively that the loss of the audio and visual oximeter (Nellcor Pulse Oximeter Model N-100) display correlated with the systolic blood pressure obtained by Doppler when the Doppler and pulse oximeter probes were on the same extremity. Subsequent studies have verified the usefulness of this methodology and have expanded it to use the disappearance and/or reappearance of the real time plethysmographic waveform available on many pulse oximeters.

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One easy way to palpate a blood pressure is to place the pulse oximeter probe on a digit in the extremity in which you’re taking a blood pressure. Wait for a steady waveform and decent saturation reading, then inflate your BP cuff. Watch the numbers as the waveform disappears, and when it reappears during deflation. Those numbers are roughly equivalent to the systolic blood pressure reading you’d obtain during conventional palpation of a blood pressure. It can be done with a manual sphygmanometer and a hand-held pulse oximeter, but it is most easily accomplished using your cardiac monitor with integrated pulse oximetry and NIBP functions. It’s not as accurate as direct auscultation, but it’s quick, and far better than simply noting the presence or absence of a distal pulse when circumstances or ambient noise keep you from obtaining anything else.

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Use of pulse oximetry for blood pressure measurement after cardiac surgery: a 1998 study:

Blood pressure measurement using pulse oximeter waveform change was compared with an oscillometric measurement and the gold standard, intra-arterial measurement, in children after cardiac surgery. Forty six patients were enrolled and divided into groups according to weight. Simultaneous blood pressure measurements were obtained from the arterial catheter, the oscillometric device, and the pulse oximeter. Pulse oximeter measurements were obtained with a blood pressure cuff proximal to the oximeter probe. The blood pressure measurements from the pulse oximeter method correlated better with intra-arterial measurements than those from the oscillometric device (0.77-0.96 v 0.42-0.83). The absolute differences between the pulse oximeter and intra-arterial measurements were significantly smaller than between the oscillometric and intra-arterial measurements in children less than 15.0 kg. The pulse oximeter waveform change is an accurate and reliable way to measure blood pressure in children non-invasively, and is superior to the oscillometric method for small patients.

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Sleep medicine:

Obstructive sleep apnoea (OSA) occurs because sleep causes the muscle tone to relax and at the level of the throat, the human airway is composed of collapsible walls of soft tissue which can obstruct breathing during sleep. One of the most common symptoms being loud snoring associated with sleepless nights and sleepiness during the day times. The definite investigation for suspected obstructive sleep apnoea is Polysomnography, which is a detailed overnight sleep study that includes recording of EEG that permit the identification of sleep at various stages. Because polysomnography is a time-consuming and expensive test, an overnight recording of arterial oxygen saturation by Oximetry can be used to confirm the diagnosis and obviate the need for a full polysomnography, although a negative result doesn’t eliminate the diagnosis but rather mandates that a patients’ needs to do a polysomnography.

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Overnight pulse oximetry:

In the past 5 years, debate has centered on the effectiveness of overnight pulse oximetry as a screening tool to identify patients with sleep-disordered breathing from the larger group of patients with simple snoring and those with excessive daytime sleepiness from other causes. This controversial discussion has arisen from needs to reduce the cost for diagnostic procedures in sleep disorders while technologic advances have made pulse oximeters handier, cheaper, and more reliable.  Pulse oximetry is a well-established tool routinely used in many settings of modern medicine to determine a patient’s arterial oxygen saturation and heart rate. The decreasing size of pulse oximeters over recent years has broadened their spectrum of use. For diagnosis and treatment of sleep-disordered breathing, overnight pulse oximetry helps determine the severity of disease and is used as an economical means to detect sleep apnea. Overnight pulse oximetry is a very useful tool for the diagnosis of sleep-disordered breathing. Authoritatively establishing a final diagnosis is very difficult without oximetry data. As a screening tool for the diagnosis of OSA, pulse oximetry is cost-effective and shows substantial accuracy. Sensitivity and specificity remain controversial, however, and deserve further clarification through controlled studies. Technical limitations, limited user knowledge, and the lack of consensus on interpretation of data all play a role in diminishing the value of pulse oximetry as a diagnostic tool.

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A flow diagram to delineate the clinical use of overnight pulse oximetry as a screening tool for sleep-disordered breathing:

In clinical practice, the number of desaturations per hour, oxygen desaturation index (ODI), is used as an important diagnostic criterion. The ODI is the number of times per hour of sleep that the SpO2 level drops by 3 percent or more from baseline. The ODI >10 demonstrated a sensitivity of 93% and a specificity of 75% to detect moderate and severe Sleep-disordered breathing.

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Diagnosis of obstructive sleep apnoea using pulse oximeter derived photoplethysmographic signals: a 2014 study:

Increasing awareness of the high prevalence of obstructive sleep apnea (OSA) and its impact on health in conjunction with high cost, inconvenience, and short supply of in-lab polysomnography (PSG) has led to the development of more convenient, affordable, and accessible diagnostic devices. Authors evaluated the reliability and accuracy of a single-channel (finger pulse-oximetry) photoplethysmography (PPG)-based device for detection of OSA (Morpheus Ox). PPG-derived data compare well with simultaneous in-lab PSG in the diagnosis of suspected OSA among patients with and without cardiopulmonary comorbidities. Use of a device such as the PPG is attractive for a number of reasons. First, it requires minimal set-up, hence making home testing extremely convenient and simple. Second, its unobtrusive nature potentially allows more normal sleep compared to traditional diagnostic modalities. Finally the device’s relative low cost can facilitate its more widespread use as well as its application for several nights’ sleep, thus potentially improving the detection rate of OSA. These advantages clearly need to be matched by proven diagnostic efficacy.

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High resolution pulse oximetry (HRPO) has been developed for in-home sleep apnoea screening and testing in patients for whom it is impractical to perform polysomnography. It stores and records both pulse rate and SpO2 in 1 second intervals and has been shown in one study to help to detect sleep disordered breathing in surgical patients. Pulse oximetry alone is not an efficient method of screening or diagnosing patients with suspected obstructive sleep apnea (OSA).  The sensitivity and negative predictive value of pulse oximetry is not adequate to rule out OSA in patients with mild to moderate symptoms. Therefore, a follow-up sleep study would be required to confirm or exclude the diagnosis of OSA, regardless of the results of pulse oximetry screening. Overnight pulse oximetry is also commonly used for the evaluation of potential hypoxemia in COPD.

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Dentistry:

Pulse Oximetry: A new tool in Pulpal Vitality Testing:

The assessment of pulp vitality is a crucial diagnostic procedure in the practice of endodontics. Conventionally, the dentist has relied on tests that depend on the patient’s perceived response to a stimulus as well as the dentist’s interpretation of that response. These methods include thermal stimulation (as in the case of heat or cold application), electric stimulation, or direct dentin stimulation (test cavity). A major shortcoming with the present pulp testing methods is that they indirectly monitor pulp vitality by measuring neural response, not vascular circulation. Stimulation of nerve fibers is not the ideal method to determine vitality status. Thus, vascular supply, not innervation, is the most accurate determinant for assessing pulp vitality. As a result, teeth that have temporarily or permanently lost their sensory function (e.g., teeth damaged by trauma) will be nonresponsive to these tests. However, they may have intact vasculature. Moreover, the nervous tissue, being highly resistant to inflammation, may remain reactive long after the surrounding tissues have degenerated. Therefore, thermal and electrical tests may give false-positive responses if only the pulp vasculature is damaged. Further, all these tests have the potential to produce an unpleasant and occasionally painful sensation, and inaccurate results may be obtained. Recent attempts to develop a method for determination of pulpal circulation have involved the use of laser Doppler flowmetry, dual-wavelength spectrophotometry, and pulse oximetry. Pulse oximetry can be used in endodontics for differential diagnosis of vital pulps and necrotic ones. This test produces no noxious stimuli, therefore, apprehensive or distressed patients may accept it more readily than routine methods.

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The critical requirement of using pulse oximeter in dentistry is as follows.

1. Sensor should conform to the size, shape, and anatomical contours of teeth.

2. Light-emitting diode sensor and the photoreceptor should be as parallel as possible to each other so that the photoreceptor sensor receives the light-emitted from LED.

3. The sensor holder should allow firm placement of the sensor onto the tooth to obtain accurate measurements

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Evaluation of efficacy of a new custom-made Pulse Oximeter Dental Probe in comparison with the Electrical and Thermal Tests for assessing Pulp Vitality: a 2007 study:

The sensitivity of the pulse oximeter was found to be 1.00, as compared to 0.81 with the cold test and 0.71 with the electrical test. The specificity of the pulse oximeter was 0.95, as compared to 0.92 with the cold and electrical pulp tests. Thus, the custom made pulse oximeter dental probe is an effective, accurate, and objective method of evaluating pulp vitality.  This in vivo study showed that the custom-built PODP is an effective, accurate, and objective method of determining the vitality of permanent teeth.

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Testicular torsion:

Potential use of Pulse Oximetry for the Diagnosis of Testicular Torsion: a 2014 study:

Scrotal Doppler ultrasonography (scrotal US) has been commonly used for evaluating patients with suspected testicular torsion (TT).  However, scrotal US is not available in all medical facilities. Comparatively, pulse oximetry is easily available at all institutions; it is used for monitoring pulse oximeter saturation (SpO2) with an accuracy equivalent to that of conventional arterial oxygen saturation (SaO2) and is the standard for noninvasive SaO2 monitoring in most medical facilities.  Authors evaluated the SpO2 and pulse rate (PR) values on the scrotums of patients undergoing exploration for TT to determine whether these values are feasible for monitoring testicular viability in TT. The results demonstrate that SpO2 values and PRs were undetectable in all of the torsed testes, in contrast to that in normal subjects. However, it may be difficult to diagnose epididymal torsion compared with TT using pulse oximetry, as the epididymis is relatively difficult to locate owing to its small size. This shortcoming may be overcome with subsequent improvements in oximetry techniques.

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The Sensor Pad attached on the Scrotal Skin Surface:

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Peripheral vascular disease:

Pulse oximetry as a potential screening tool for lower extremity arterial disease in asymptomatic patients with diabetes mellitus: a 2005 study.

Lower extremity arterial disease (LEAD) is common and underdiagnosed in patients with diabetes mellitus and is associated with higher total mortality. Authors compared the accuracy of pulse oximetry, the ankle-brachial index (ABI), and the combination of the two to diagnose LEAD in consecutive outpatients with type 2 diabetes who had no symptoms of LEAD, in a primary care setting.  Pulse oximetry of the toes seems as accurate as ABI to screen for LEAD in patients with type 2 diabetes. Combination of the two tests increases sensitivity.

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A prospective comparison of bilateral photoplethysmography versus the ankle-brachial pressure index for detecting and quantifying lower limb peripheral arterial disease: a 2008 study:

This study prospectively assessed the diagnostic accuracy of a novel bilateral photoplethysmography toe pulse measurement technique for the detection of significant lower limb peripheral arterial disease. Bilateral photoplethysmography toe pulse measurements were compared with the ankle-brachial pressure index (ABPI) gold standard reference. Pulse wave analysis techniques extracted timing, amplitude, and shape characteristics for the great toes and their right-to-left side differences. These characteristics were compared with previously obtained normative ranges, and the accuracy was assessed for all significant disease (ABPI <0.9) and higher-grade disease (ABPI <0.5). The degree that pulse shape fell beyond the normal range of normalized pulse shapes was at the threshold of substantial to almost perfect agreement compared with ABPI for significant disease detection (diagnostic accuracy, 91% [kappa = 0.80]; sensitivity, 93%; specificity, 89%), and with 90% accuracy (kappa = 0.65) for higher-grade disease detection. Pulse transit time differences between right and left toes also had substantial agreement with ABPI, with diagnostic accuracy of 86% for significant disease detection (pulse transit time to pulse foot [kappa = 0.71] and to pulse peak [kappa = 0.70]) and reached at least 90% for these for the higher-grade disease. With the shape and pulse transit time measurements, the negative-predictive values of the 5% disease population screening-prevalence level were at least 99% and had positive-predictive values of at least 98% for the 90% disease-prevalence level for vascular laboratory referrals. This simple-to-use technique could offer significant benefits for the diagnosis of peripheral arterial disease in settings such as primary care where noninvasive, accurate, and diagnostic techniques not requiring specialist training are desirable. Improved diagnosis and screening for peripheral arterial disease has the potential to allow identification and risk factor management for this high-risk group.

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Diagnostic importance of pulse oximetry in the determination of the stage of chronic arterial insufficiency (CAI) of lower extremities: a 2010 study:

The aim of this work was to determine the diagnostic importance of pulse oximetry in the early detection of stage of lower extremities CAI based on peripheral arterial oxygen saturation of haemoglobin (SpO2). Using pulse oximetry, depending on the stage of lower extremities CAI, authors revealed a considerable difference in the stages of functional ischemia. In 3 patients with gangrenous foot and fingers, SpO2 was immeasurable and progressive decrease in SpO2 of arterial capillaries (p < 0.01 between stages). Due to the reliability and simplicity of pulse oximetry it can be a routinely used diagnostic device for patients with early determined stage of lower extremities CAI.

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Collateral blood flow:

Pulse oximetry compared with Doppler ultrasound for assessment of collateral blood flow to the hand: a 2007 study:

Ischaemic injury to the hand after arterial cannulation is a rare but well documented complication and routine testing of the adequacy of collateral circulation is widely advocated. The widespread availability of the pulse oximeter in the operating theatre, its applicability in circumstances where the patient is unable to cooperate, and its dependence on pulsatile blood flow suggest that this device could potentially be usefully applied to the assessment of collateral blood flow. The reliability of the pulse oximeter to detect the presence or absence of collateral circulation was prospectively compared to Doppler ultrasound in 109 hands from 64 adult patients. Nine hands demonstrated inadequate ulnar collateral flow, one hand demonstrated inadequate radial collateral flow and a persistent median artery was found in one hand. In all patients the results of pulse oximeter testing (probe placed on the thumb) correlated precisely with the results obtained with the Doppler device (probe located over the lateral aspect of the superficial palmar arch). These results demonstrate pulse oximetry to be a reliable method of assessing collateral blood flow to the hand before arterial cannulation.

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You can also use your pulse oximeter to continuously evaluate distal circulation in an injured extremity. If you’ve splinted a fractured limb, or applied a pressure dressing to a laceration, make it a point to place your pulse oximeter probe on a digit in the injured extremity. As long as it gives you a numerical readout and a waveform, you can reasonably assume that distal circulation is adequate.

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Pulse oximetry as screening tool of aspiration:

Dysphagia is common after stroke, occurring in 25% to 42% of patients. About one third of patients with dysphagia aspirate food or fluid into their airways, and in 40% of them aspiration is silent (i.e., it does not trigger a cough or cause symptoms or signs of distress).  Detection of silent aspiration is important because aspiration often leads to such serious complications as pulmonary infections, septicemia, dehydration, and malnutrition. There are no reliable clinical signs of silent aspiration, and aspirating patients frequently do not complain of swallowing difficulties.  Furthermore, bedside assessment of dysphagic patients, unless coupled with an objective method such as videofluoroscopy or nasal endoscopy, often fails to detect silent aspiration. Although nasal endoscopy detects silent aspiration in nearly all patients, the procedure requires a certain degree of expertise and is time consuming and sometimes poorly tolerated by patients. Similarly, videofluoroscopy is not suitable for routine clinical use, especially when repeated assessments of severely ill patients are required.  In recent years, pulse oximetry has been advocated as an alternative to nasal endoscopy and videofluoroscopy for the assessment of dysphagic patients. It has been suggested that aspiration of food or fluid into the airways causes reflex bronchoconstriction that leads to ventilation-perfusion mismatch and oxygen desaturation of arterial blood, which can be readily measured by pulse oximetry.  Pulse oximetry is noninvasive, simple, and repeatable, and it does not involve exposure to radiation. However, the value of this method in the diagnosis of silent aspiration has yet to be fully examined. In 49 patients with stroke, Zaidi et al studied oxygen saturation after the swallowing of 10 mL of water. They then compared the pulse oximetry results with the findings of bedside assessment by an independent speech and language therapist. The authors found a close correlation between aspiration as diagnosed clinically by the therapist and the drop in arterial blood oxygen saturation measured by pulse oximetry. However, the authors did not perform the dysphagia assessment simultaneously with the pulse oximetry. This poses a problem with the interpretation of their data, as aspiration may occur intermittently. Furthermore, the subjective clinical evaluation of dysphagia is unreliable: 42% to 60% of patients aspirating food or fluid are not recognized.  Four studies compared oxygen saturation levels with video fluoroscopy, three being simultaneous. Of these, two have suggested that pulse oximetry may be useful in diagnosing aspiration. The others have been more cautious, but there is sufficient support to warrant further research. In a recent study, Colodny compared pulse oximetry with ®bre-optic endoscopic evaluation in 104 subjects and found no relationship between SpO2 levels and aspiration. She did, however, conclude that pulse oximetry may be used as an adjunct to discriminate dysphagia from non-dysphagia.

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Pulse oximetry does not reliably detect aspiration on videofluoroscopic swallowing (VFSS) study: a 2014 study:

Simultaneously monitoring the arterial oxygen saturation (SpO2) by pulse oximetry is done while patients were performing VFSS. A decrease in SpO2 exceeding 3% was considered as significant desaturation. Bolus or portion of bolus passing through the vocal cords and entering the subglottic space was defined as aspiration on VFSS. The results of pulse oximetry and VFSS were compared. No significant correlation existed between desaturation measured by pulse oximetry and aspiration on VFSS (χ2 test, P=0.87). The positive predictive rate of pulse oximetry in detecting aspiration on VFSS was 39.1%, and the negative predictive rate was 59.4%. Aspiration occurring on VFSS cannot be predicted based on decrease in SpO2 in pulse oximetry. The application of pulse oximetry to detect aspiration during regular meals requires further investigation.

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Accuracy of pulse oximetry:

Numerous studies have addressed the accuracy of pulse oximeters, primarily over the range of 70% to 100% saturation. Excellent correlation has been found between pulse oximetry and the “gold standard” in vitro Co-oximetry measurements. These have been found to be accurate for SpO2 from 70% to 100% and within ± 2%. For SpO2 above 70%, approximately 68% of the data will fall within ±2% of the actual saturation, and 95% of the data will fall within ±4% of the actual saturation. For example, in a patient with a pulse oximeter reading of 92%, 95% of the time the true SaO2 value, as measured by arterial blood gases, would be between 88% and 96%. For saturations below 70%, manufacturers generally state that accuracy is “unspecified.” Pulse – rate monitoring with pulse oximetry ranges from 20 to 30, to 250 beats per minute, with manufacturers accuracy statements indicating a range from ±1 to 2 beats per minute for the scale stated.  Once in use, there is little evidence that pulse oximeters are ever re-calibrated or have their accuracy assessed. A high reliance is placed upon the continuing reliability of the wavelength of the light emitted from the LEDs. Should the wavelength of the light emitted by one or both LEDs alter, the degree of absorption will alter and the R value will change. The mathematical algorithm contained within the pulse oximeter software for the estimation of SpO2 will then be fed incorrect information, and an inaccurate estimation of SpO2 will be displayed on the monitor. This may in turn lead to incorrect diagnosis and treatment of a patient. The common manufacturing literature claim for accuracy for pulse oximeters is ± 2–3% SpO2 over a declared range of 70–100%, and the International Standard for pulse oximeter manufacture ISO 80601-2-61-2011 requires an accuracy of ≤ 4% error in this range.

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Pulse oximeter accuracy, along with clinical reliability are the two most important parameters to consider when choosing a technology for the critical task of monitoring the oxygenation of patients. To establish their accuracy claims for market clearance by the FDA, pulse oximetry manufacturers provide data from studies done in their laboratory on healthy volunteers. In order for accuracy claims made by a manufacturer to be clinically meaningful they must be validated by independent, clinical research. It is not until the technology is tested by independent investigators on patients in clinical settings or on volunteers during challenging physiological conditions where the SpO2 readings are compared against arterial blood analysis, that the “working accuracy” of the pulse oximetry technology is truly revealed. Pulse oximetry estimates arterial hemoglobin oxygen saturation (SaO2) from the ratio of the pulsatile to the total transmitted red light divided by the same ratio for infrared light transilluminating a finger, ear, or other tissue. The SaO2 estimated by pulse oximetry (SpO2) may not be independent of skin pigmentation and many other variables, such as haemoglobin concentration, nail polish, dirt, and jaundice.  So numerous factors can influence the accuracy of pulse oximeters in the clinical environment. During the empirical calibration of pulse oximeter systems, great care is taken to only use volunteers with normal levels of carboxyhemoglobin (COHb) and methemoglobin (MetHb) because values above 2 to 3% COHb and 1 to 1.5% MetHb seen clinically, will affect the accuracy of the SpO2 measurements. Additionally, body temperature can cause as much as a 3% difference in the SpO2 measurements. Digits that are warm (> 30 °C) may read 96 to 97% SPO2 while cold digits (< 20 °C) may read 99 to 100% SpO2 in the subject at the same PaO2. This phenomenon is thought to be due to arterial to venous (A-V) shunting in the digits. A-V shunts may be open in warm hands causing “venous pulsations” which result in a lower SPO2 compared to cold hands with no A-V shunting. That is why the empirical calibration is always done on normothermic volunteers. There are conflicting studies regarding the effect on skin pigment and painted fingernails on the accuracy of pulse oximeters. Thus numerous factors can cause the pulse oximeter system to exceed its specified accuracy in actual patients. Because all manufacturers submit similar data from normal healthy volunteers to the FDA for market clearance, one can expect pulse oximeters from various manufacturers to perform similarly on healthy subjects or patients who are not physiologically compromised. However, factors such as motion and low perfusion in patients that are compromised can significantly affect the accuracy of SpO2 measurements. Thus, when evaluating the accuracy of a device it is important to review published clinical studies that test the performance of the device on compromised patients. A device that is marketed to have accuracy of + 2% in the 70% to 100% range may not achieve those results on a poorly perfused patient, or even worse, a poorly perfused, moving patient. Likewise, a device that has an accuracy claim of + 3% from 60% to 80% (for healthy adult volunteers) may not accurately display data on a cyanotic congenital heart disease infant whose SaO2 is chronically below 80%. For this reason, pulse oximeters need to be tested in all these clinical populations.

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Bias and precision:

Bias is the mean difference between SaO2 and SpO2. Precision is defined as the standard deviation (SD) of the differences between SaO2 and SpO2. In the 1980s, pulse oximeter manufacturers stated their accuracy as 2% or 3% (+ 1 SD), where + 1 SD mathematically represents approximately two thirds of the population. Therefore, a device and sensor combination with a 3% (+ 1 SD) accuracy, would have results that were within + 3% (digits) 2/3 of the time. Thus if the actual SaO2 is 94%, a device with + 3% accuracy can be expected to read SpO2 values between 91% to 97% approximately 2/3 of the time. Recently, the FDA has required manufacturers to report their accuracy based on an accuracy specification metric referred to as ‘root mean square’ which reports accuracy as a function of both bias and precision. The root mean square is calculated by taking the square root of the sum of the square of the bias plus the square of the precision.

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Pulse Oximetry accuracy as a reflection of Arterial PO2 is impacted by the Sigmoidal Shape of the Oxyhemoglobin Dissociation Curve. At high levels of Oxygenation, Pulse Oximetry is insensitive at detecting significant changes in PaO2: since these are being measured in the flat part of the oxyhemoglobin dissociation curve.

Example 1: the PaO2 could drop from 150 to 70 mmHg without an appreciable change in the SpO2, as this change occurs over the flat part of the oxyhemoglobin dissociation curve

Example 2: once hemoglobin is 100% saturated, no further increase in the PaO2 will be reflected in the SpO2 –this makes SpO2 poor at quantifying the degree of hyperoxemia.

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An assessment of the accuracy of pulse oximeters: a 2012 study:

Peripheral pulse oximetry has become a core monitoring modality in most fields of medicine. Pulse oximeters are used ubiquitously in operating theatres, hospital wards, outpatient clinics and general practice surgeries. This study used a portable spectrometer (Lightman®, The Electrode Co. Ltd., Monmouthshire, UK) to measure the emission spectra of the two light emitting diodes within the pulse oximeter sensor and to determine the accuracy of 847 pulse oximeters currently in use in 29 NHS hospitals in the UK. The standard manufacturing claim of accuracy for pulse oximeters is ± 2–3% over the range of 70–100% SpO2. Eighty-nine sensors (10.5%) were found to have a functional error of their electrical circuitry that could cause inaccuracy of measurement. Of the remaining 758 sensors, 169 (22.3%) were found to have emission spectra different from the manufacturers’ specification that would cause an inaccuracy in saturation estimation of > 4% in the range of 70–100% saturation. This study has demonstrated that a significant proportion of pulse oximeter sensors may be inaccurate.

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Limitations, errors and problems with pulse oximetry:

Oximetry is not a complete measure of respiratory sufficiency. A patient suffering from hypoventilation (poor gas exchange in the lungs) given 100% oxygen can have excellent blood oxygen levels while still suffering from respiratory acidosis due to excessive carbon dioxide. It is also not a complete measure of circulatory sufficiency. If there is insufficient blood flow or insufficient hemoglobin in the blood (anemia), tissues can suffer hypoxia despite high oxygen saturation in the blood that does arrive. Pulse oximetry measures solely hemoglobin saturation, not ventilation and is not a complete measure of respiratory sufficiency. It is not a substitute for blood gases checked in a laboratory, because it gives no indication of base deficit, carbon dioxide levels, blood pH, or bicarbonate (HCO3−) concentration. The metabolism of oxygen can be readily measured by monitoring expired CO2, but saturation figures give no information about blood oxygen content. Most of the oxygen in the blood is carried by hemoglobin; in severe anemia, the blood will carry less total oxygen, despite the hemoglobin being 100% saturated. Pulse oximeters do not require user calibration. Thus, it is important that users of the device are aware of the inherent limitations that may give false readings. The pulse oximeter will function properly only if it is able to detect a modulation in transmitted light. If perfusion is decreased and pulse amplitude is small, the signal will be decreased, and the device will be liable to error or be unable to obtain a reading. During cardiac arrest peripheral pulses may be so weak that the device cannot detect them, so monitoring SpO2 by pulse oximetry could be contraindicated. Pulse oximetry has been found to be reliable with systolic blood pressure readings greater than 80 mm Hg. Hypotensive systolic blood pressure readings less than 80 mm Hg cause inaccurate and unreliable pulse oximetry readings. Hypotension, low cardiac output, vasoconstriction, vasoactive drugs (dobutamine or dopamine), and hypothermia all reduce tissue blood flow. These low perfusion states produce a low signal-to-noise ratio and create a signal that can be altered by artifact. Lowered perfusion reduces the signal strength, and the oximeter may not be able to adequately differentiate between arterial pulsations and background noise. This causes inaccurate readings, because the sensor is unable to distinguish the true signal. Conversely, increased venous pulsation, such as occurs with tricuspid regurgitation may be misread by the pulse-oximeter as arterial blood, with a low resultant reading. Motion artifact can interfere with signal detection and interpretation of the signal by the device because of an unstable waveform. Improperly seated sensors, shivering, seizures, or parkinsonian tremors can cause movement, creating an inaccurate reading. Adjustment of the device to a longer signal averaging time may reduce the effects of motion artifact. The pulse oximeter may also be inaccurate in bradycardia and irregular cardiac rhythms, because the device is not able to average the signal waveform in the set amount of time. Edema or venous congestion of the limb can also interfere with readings because of decreased signal. Because pulse oximeters use two-wavelength spectrophotometry, readings are inaccurate in the presence of abnormal hemoglobin levels. Thus, carbon monoxide poisoning will result in an erroneous SpO2 reading as a result of carboxyhemoglobin. Smokers will often have artificially high readings after smoking a cigarette because cigarette smoke contains carbon monoxide. The presence of methemoglobin will also give an unreliable oximeter reading.

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Safe versus unsafe limitations of pulse oximetry:

Pulse oximeters rarely cause any harm directly, though apparently some older models could cause burns and there are reports of the probes causing pressure ulcers. However if their limitations are not borne in mind, harm could be caused by someone having the wrong (or no) treatment. So it’s important to know what the limitations are. Safe limitations are circumstances in which a possible inaccuracy in the displayed SpO2 can be easily suspected; the observer is usually warned by the device (alarm) about the pitfall. Potentially unsafe limitations are those situations in which the inaccuracy is difficult to recognize; the displayed SpO2 is erroneous but the observer is not warned about the pitfall. One limitation is that pulse oximeters cannot operate reliably with a poor signal. This has been referred to as a ‘safe’ limitation, in that the pulse oximeter is not able to give an accurate reading but in some way indicates this fact. Obviously pulse oximeters need to be technically capable of indicating this and the person using it must be aware of this point. The other sort of limitation is more dangerous in that the pulse oximeter may appear to have a good signal and be displaying a saturation figure, but either the figure is inaccurate or gives a false sense of security.

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Limitations Mechanism Bias Proposed Action
Safe limitations
    Motion Sensor movement Lower SpO2 readings Evaluate plethysmographic waveform
Increased noise caused by changes in nonpulsatile component of light absorption False alarms Stabilize sensor
Change sensor position
Use new-generation pulse oximeters
    Poor perfusion Decreased signal caused by decreased pulsatile (arterial) component of light absorption Lower SpO2 readings Evaluate plethysmographic waveform
Check and correct skin temperature and peripheral perfusion
Place sensor more centrally
Use new-generation pulse oximeters
    Skin pigmentation Probably caused by calibration assumptions for dark skin pigmentation Lower or less reliable SpO2 readings at lower SaO2 values Use new-generation pulse oximeters
    Nail polish and artificial nails Decreased signal because of decreased light absorption with artificial nails or nail polish of black, blue, or green color Lower SpO2 readings Change sensor position
    Irregular rhythms Increased noise caused by tachyarrhythmias Lower or less reliable SpO2 readings Evaluate plethysmographic waveform
Use new-generation pulse oximeters
    Electromagnetic interference External electromagnetic energy interference caused by electrosurgical cauterization units, cellular phones, or MRI devices Lower SpO2 readings Evaluate plethysmographic waveform
False alarms Avoid external electromagnetic energy sources
Heating of the sensor and thermal injury (MRI) Use pulse oximeters with fiber-optic technology (MRI)
Potentially unsafe limitations
    Calibration Device-specific calibration algorithms derived by correlating light absorption ratios over a SaO2 spectrum of 80%–100% in healthy young adults SpO2 readings of <80%–85% are less accurate especially at the extremes of the age spectrum Use new-generation pulse oximeters
Lower SpO2 values calculated by mathematical equations
    Time lag Software-related delay between sudden changes in blood oxygenation and SpO2 readings Delay in detecting clinically important desaturation, which may exceed 15–20 s Use new-generation pulse oximeters
Do not use pulse oximetry as a substitute for cardiorespiratory monitoring in critically ill patients
    Probe positioning The emitted light energy is projected tangentially to the detector because of inappropriate sensor placement (“penumbra” or “optical shunting” effect) Lower SpO2 readings Place sensor with the emitter and the detector exactly opposite to each other
Use probes of appropriate size in neonates and infants
      light interference Intense external light energy (as in phototherapy) may interfere with the photodetector (“flooding” effect) Lower SpO2 readings Use new-generation pulse oximeters
Cover the sensor
    Abnormal hemoglobin molecules COHb presents red-light absorption similar to oxyhemoglobin In carboxyhemoglobinemia pulse oximetry overestimates blood oxygenation Check arterial SaO2 if abnormal hemoglobin molecules are suspected (i.e., carbon monoxide intoxication)
Methemoglobin absorbs equal amount of energy in the red and infrared spectra, which affects the ratio of absorption In significant methemoglobinemia, SpO2 tends toward 85% Suspect abnormal hemoglobin molecules if the SaO2–SpO2 difference exceeds 5%
Use pulse co-oximetry
    Pulsatile veins Increased noise because of pulsations of venous blood (i.e., significant tricuspid regurgitation, hyperdynamic circulation states) Lower or less reliable SpO2 readings Use new-generation pulse oximeters
    Intravenous dyes Intravenous dyes such as methylene blue, indocyanine green, and indigo carmine interfere with light absorption Lower SpO2 readings Do not use pulse oximetry or interpret pulse-oximetry readings with caution
Check SaO2

New-generation pulse oximeters are less susceptible to these limitations because of more sophisticated calibration and signal-extraction algorithms. Pulse co-oximeters are capable of detecting abnormal hemoglobin molecules by using multiwavelength technology.

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Limitations of pulse oximetry in detail:

Poor signal:

Pulse oximeters need a strong regular pulse in the finger (or ear etc.) that the probe is on. A common problem is that during cold weather people can have cold hands and feet, and have peripheral vasoconstriction. In this case a pulse oximeter may display a reading but it might not be accurate. Some pulse oximeters have a means of indicating how strong the signal is they are receiving and it is important to check this. A still weaker signal may mean the pulse oximeter is not able to work at all. An irregular signal can also cause problems for a pulse oximeter trying to determine oxygen saturation. This can be caused by an irregular heart beat or by the patient moving, shivering or fitting. Poor positioning of the probe can cause inaccurate readings due to various problems. This can be a particular problem with very small fingers and very large ones. Make sure the probe is well on the finger. If the probe is not properly attached, it may detect a variety of noise, resulting in inaccurate measurement.

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Problem of movement:

When you think of problems associated with pulse oximeters it is important to remember that the signal that is analyzed is really tiny. As explained earlier, it is only about 2 % of the total light that is analyzed. Which such a small signal, it is easy to see how errors can occur. Pulse oximeters are very vulnerable to motion, such as a patient moving his hand especially in recovery room. As the finger moves, the light levels change dramatically. Such a poor signal makes it difficult for the pulse oximeter to calculate oxygen saturation. Motion artifact can be a significant limitation to pulse oximetry monitoring resulting in frequent false alarms and loss of data. The reason for this is that during motion and low peripheral perfusion, many pulse oximeters cannot distinguish between pulsating arterial blood and moving venous blood, leading to underestimation of oxygen saturation. Early studies of pulse oximetry performance during subject motion made clear the vulnerabilities of conventional pulse oximetry technologies to motion artifact.

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Problem of optical shunting:

The pulse oximeter operates best when all the light passes through arterial blood. However, if the probe is of the wrong size or has not being applied properly, some of the light, instead of going through the artery, goes by the side of the artery (shunting). This reduces the strength of the pulsatile signal making the pulse oximeter prone to errors. It is therefore important to select the correct sized probe and to place the finger correctly in the chosen probe for best results.

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Problem of too much ambient light:

As discussed before, in addition to the light from the LEDs, ambient (room) light also hits the detector. For good functioning of the pulse oximeter, the strength of the LED light falling on the detector should be good when compared with the strength of the ambient light falling on the detector. If the ambient light is too strong, the LED light signal gets “submerged” in the noise of the ambient light. This can lead to erroneous readings. Therefore, it is important to minimise the amount of ambient light falling on the detector. One can try and move away strong sources of room light. One can also try and cover the pulse oximeter probe and finger with a cloth etc. Light from heat lamps and phototherapy lights has been reported to skew the readings. The high intensity of light emitted from these sources masks the small changes in light transmission from the probe. The remedy is to shield the probe from the ambient light by black paper (e.g. carbon paper) or black polythene or aluminium foil.

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The 2 wavelengths sensed by the oximeter probe (660 nm and 940 nm) can be generated (in various proportions) by several ambient light sources commonly used in clinical settings. For example, the spectrum of energy produced by both quartz-halogen and incandescent bulbs begins in the visible range, at 650 nm, and peaks around 1,000 nm. An infrared heat lamp, with spectral output beginning at approximately 700 nm, generates little energy in the visible (red) range. In contrast, bilirubin and fluorescent light sources emit more energy at shorter wavelengths and minimal energy in the infrared range. Bilirubin light peaks around 200–400 nm. Fluorescent light produces most of its energy in the visible range: 405–579 nm. Since pulse oximetry depends on accurate measurement of the 660–940 nm range and quartz-halogen, incandescent, infrared, fluorescent, and bilirubin bulbs produce wavelengths in that range, those light sources could, theoretically, affect pulse oximetry readings.

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Does Ambient Light affect the accuracy of Pulse Oximetry? A 2003 study:

Forty-five faculty and students at a university, none of whom had pale skin, dark skin, or evidence of cardiopulmonary disease were included in study. Any nail polish was removed.  Five light sources were individually tested: incandescent, quartz-halogen, infrared, fluorescent, and bilirubin light. A pulse oximetry probe was placed on the subject’s finger, and the finger and probe were placed sideways under each light source, on a predetermined mark.  The greatest difference in pulse oximetry reading between any of the light sources was 0.5%. Repeated-measures analysis of variance yielded a p value of 0.204.  Ambient light has no statistically significant effect on pulse oximetry readings. Even had the differences been statistically significant, the magnitude of the differences was small and thus clinically unimportant. Pulse oximeter readings are not significantly affected by 5 light sources commonly found in the clinical setting.

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Problem of electromagnetic interference:

Electrical equipment such as surgical diathermy emit strong electric waves which may be picked up by the wires of the pulse oximeter. These waves make small currents form in the wires, confusing the pulse oximeter which assumes these currents come from the light detector. During diathermy use, one should be cautious about interpreting pulse oximeter readings. If electric appliances such as televisions, mobile telephones, or medical devices which produce high levels of electromagnetic waves are used near the pulse oximeter, the electromagnetic waves from these devices may interfere with accurate measurement. Radiofrequency emissions from MRI scanners (and electrocautery devices) may interfere with pulse oximetry. In addition, 2nd/3rd-degree burns beneath pulse oximeter probes have been reported in patients undergoing MRI scans due to generation of electrical skin currents beneath the looped pulse oximeter cables, which act as an antenna.

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Problem of poor peripheral perfusion:

A good peripheral blood flow makes the arteries in fingers nicely pulsatile. As discussed before, it is the pulsatile change in absorbance that is used in the calculation of oxygen saturation. When the peripheral perfusion is poor (e.g. in hypotension), the arteries are much less pulsatile. The change in absorbance is therefore less and the pulse oximeter may then find the signal inadequate to correctly calculate oxygen saturation.

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A reduction in peripheral pulsatile blood flow produced by peripheral vasoconstriction (hypovolaemia, severe hypotension, cold, cardiac failure, some cardiac arrhythmias) or peripheral vascular disease result in an inadequate signal for analysis. Venous congestion, particularly when caused by tricuspid regurgitation, may produce venous pulsations which may produce low readings with ear probes. Venous congestion of the limb may affect readings as can a badly positioned probe. When readings are lower than expected it is worth repositioning the probe. In general, however, if the waveform on the flow trace is good, then the reading will be accurate.

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Problem of not detecting hyperoxia:

The problem is that the pulse oximeter cannot “see” the extra dissolved oxygen. When PaO2 is higher than 100 mm due to supplemental oxygen, the saturation still shows 100 %, instead of say 120 %. The 100 % saturation tells us that the patient is getting enough oxygen. However, it does not tell you that the patient is getting too much oxygen (hyperoxia). Oxygen, while necessary for life, can be harmful if given in excess. Therefore, other means (e.g. arterial blood gas) have to be used to detect hyperoxia.

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Delay:

Pulse Oximetry measurements are signal averaged over several seconds. Therefore, the pulse oximeter may not detect a hypoxemic event until several seconds after it has occurred: this may be particularly important when the pulse oximeter is being used to monitor SpO2 during intubation.

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Anemia:

In theory there is no reason anaemia should cause pulse oximeters to be inaccurate and experiments in dogs have shown accuracy reliable enough for “clinical purposes” as long as the packed cell volume was larger than 15%. Clinical experience has shown good performance with haemoglobin as low as 2.3 g/dl. However in severe anemia (with Hb <5 g/dL) with SaO2 <80%, SpO2 underestimates the SaO2: this may be due to increased signal/noise ratio from the surrounding tissue.  A 1990 study of retrospective evaluation of simultaneous tests of oximeters of various manufacturers in volunteer subjects disclosed greater errors at low saturations in subjects with low hemoglobin (Hb) concentrations. The error due to anemia was zero at 97% SaO2 and became evident when SaO2 fell below 75%.

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Sickle cell disease:

It has been shown that pulse oximetry can detect low oxygen saturation accurately in sickle cell disease, however other researchers have suggested caution in interpreting pulse oximetry values in sickle cell disease.

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Pulse Oximetry and factors associated with Hemoglobin Oxygen Desaturation in children with Sickle Cell Disease: a 1993 study:

Authors conclude that pulse oximetry may be useful to assess whether progressive pulmonary dysfunction begins at an early age in Hb SS patients, and to assess acutely ill patients for the presence of hypoxemia associated with acute chest syndrome.

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Accuracy of Pulse Oximetry in Sickle Cell Disease: a 1999 study:

This study confirms in adults that pulse oximetry has acceptable accuracy for reliable clinical diagnosis of serious gas exchange abnormalities in sickle cell disease. Despite patients’ severe anemia, which has been shown to impair the accuracy of pulse oximetry, as long as strong and regular photoplethysmographic waves were present, authors found that pulse oximeters could be relied upon not to misdiagnose either hypoxemia or normoxemia in such patients. As in all other patients, additional tests for the severity of anemia, the adequacy of cardiac output, and sometimes the carboxyhemoglobin (and met-hemoglobin) levels are required for full evaluation of oxygen transport.

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Carbon dioxide:

A pulse oximeter can cause a false sense of security by giving a good saturation figure when someone’s breathing is completely inadequate. This is especially true when a patient is getting supplementary oxygen. There are two main functions of breathing, one is getting oxygen out of the air and into the body, the other is getting carbon dioxide out of the body and into the air. It possible for someone to be getting enough oxygen into their body but not be getting rid of enough carbon dioxide. Oxygen saturation by itself does not tell the whole story about breathing – this is especially true if someone is being given oxygen. During acute hypoventilation, the PCO2 can rise significantly before desaturation occurs on the SpO2: this is especially true if the patient is receiving supplemental oxygen, in this case, the PCO2 can continue to rise while the SpO2 is artificially “supported” by the supplemental oxygen. As a minimum it is also necessary to record the respiratory rate, and if they are having oxygen, how much they are having. Pulse Oximetry does not measure PCO2 or pH and gives no information about ventilation.

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Problem of coloured dyes and nail polish:

The dye, methylene blue, if in the patient’s circulation, will artificially lower the displayed oxygen saturation. When methylene blue is used in surgery to the parathyroids or to treat methaemoglobinaemia a shortlived reduction in saturation estimations is registered. Finger nail polish can affect the accuracy of saturation determination. Nail varnish may cause falsely low readings.

Nail varnish:

Some research has shown that dark nail varnish bias pulse oximeter readings, but not by a clinically significant amount. However there are limitations to this research such as a lack of trials at lower saturations, so in practice nail varnish should still be removed.

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The effect of nail polish and acrylic nails on pulse oximetry reading using the Lifebox oximeter in Nigeria: a 2013 study:

Fifty non-smoking volunteers had their fingers numbered from right to left (little finger of right hand =1 and little finger of left hand =10). Alternate fingers were nails painted with clear, red, brown and black nail polish and the 5th finger had acrylic nail applied. The corresponding finger on the other hand acted as control. The oxygen saturation was determined using the Lifebox pulse oximeter. All fingers (100%) with clear nail polish, red nail polish and acrylic nails recorded a saturation value. Each of the mean saturation value for clear nail polish, red nail polish and acrylic nails was not significantly different from the control mean (p= 0.378, 0.427 and 0.921). Only 12% and 64% of nails polished black and brown respectively recorded a saturation value. The mean SpO2 for black and brown polish were significantly different from their control mean (p<0.001). Black and brown polish resulted in a significant decrease in SpO2 with the Lifebox oximeter. Dark coloured nail polish should be removed prior to SpO2 determination to ensure that accurate readings can be obtained.

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Skin pigmentation:

Previous research on pulse oximetry has found that skin pigmentation has no clinically significant effect. Recently however it has been found that pulse oximeters from three manufacturers overestimated oxygen saturation in individuals with darkly pigmented skin at saturations below 80%. The authors suggested that pulse oximeters should carry a warning about this. Above 80% the researchers concluded that the effect was probably of no clinical significance.

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Bilirubin:

The literature concerning the effect of bilirubin on oximetry can appear confused. Two authors state that bilirubin can affect pulse oximetry readings, but neither give any evidence or references to support this. Moyle in the authoritative ‘Pulse Oximetry’ reviews the subject and concludes that pulse oximetry is accurate, but that co-oximetry – the usual ‘gold standard’ method of verifying pulse oximeter readings – is not. This last point is supported by two case studies, the authors of which feel “… in the presence of severe hyperbilirubinemia, pulse oximetry may be more accurate than co-oximetry”. Abrams et al looked at pulse oximetry in patients with liver disease. They found that pulse oximetry overestimated oxygen saturation as measured by a co-oximeter in both their subjects and their controls.  Veyckmans et al carried out research on the influence of bilirubin on pulse oximetry and concluded “There was no demonstrable direct influence of high bilirubin plasma levels on SpO2 as measured by a Nellcor (r) pulse oximeter”.

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Dyshemoglobinemia:

The dyshemoglobinemia are a constellation of disorders in which the hemoglobin is functionally altered and prevented from carrying oxygen. They include carboxyhemoglobin, methemoglobin and sulfhemoglobin. Since pulse oximetry only measures the percentage of bound hemoglobin, a falsely high or falsely low reading will occur when hemoglobin binds to something other than oxygen.

•Hemoglobin has a higher affinity to carbon monoxide than oxygen, and a high reading may occur despite the patient actually being hypoxemic. In cases of carbon monoxide poisoning, this inaccuracy may delay the recognition of hypoxia.

•Methemoglobinemia characteristically causes pulse oximetry readings in the mid-80s.

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Carbon monoxide (CO):

Carbon monoxide is a colourless, odourless gas that is produced in most fires. Breathing in carbon monoxide will lead to it becoming attached to haemoglobin in preference to oxygen, so it is only necessary to breath in a small amount of carbon monoxide to have a large amount of haemoglobin taken up by it and therefore not available to carry oxygen. For instance if 25% of someone’s haemoglobin is taken up by carbon monoxide then only 75% is available to carry oxygen, and so their oxygen saturation could, at best, be only 75%. Pulse oximeters will display an oxygen saturation which is approximately equal to the percentage of haemoglobin combined with oxygen plus the percentage of haemoglobin combined with carbon monoxide. So if someone has 25% of their haemoglobin saturated with carbon monoxide and true oxygen saturation of 70% a pulse oximeter will display an oxygen saturation of about 95%. This is obviously extremely dangerous and for this reason pulse oximeters should not be used with people who may have inhaled smoke, i.e. anyone who has been involved with any sort of fire, unless you are certain that they do not have any significant level of carbon monoxide in their blood.

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Carboxyhemoglobin does not carry oxygen. It is really a hemoglobin molecule with all oxygen carrying sites occupied by CO. The CO has such a high affinity for hemoglobin, that oxygen cannot displace it.  CO has about 240 times the affinity of O2 for Hemoglobin and binds to same sites. Consider carboxyhemoglobin totally useless in oxygen transport. The presence of COHb also shifts the O2 dissociation curve to the left, thus interfering with the unloading of O2.  This is an additional feature of the toxicity of CO. CO poisoning results from CO exposure, most commonly exposure to fuel combustion (fuel burning heaters, stoves, automobile exhaust, etc.), so it most commonly occurs during cold periods where people are in closed quarters to conserve the heat originating from fuel combustion. Symptoms include headache, nausea, vomiting and weakness. The patient is classically described as cherry red, but in reality, they appear to be pink, which lowers the clinician’s suspicion for hypoxia. Thus, these symptoms are commonly attributed to viral flu-like illnesses. If a patient has a carboxyhemoglobin level of 25%, and their hemoglobin is 12, this means that they effectively have a hemoglobin of only 9 (since 25% of their hemoglobin is useless). If the carboxyhemoglobin level is 25%, then the maximum oxygen saturation that can be attained is 75%. However, the pulse oximeter will read 100% because light absorption characteristic of carboxyhemoglobin is similar to oxyhemoglobin. Thus, pulse oximetry measurements are fooled by CO poisoning. The arterial blood gas is not usually helpful either. Since the ABG measures oxygen gas tension (PaO2) and not oxygen content or true oxygen saturation, the oxygen gas tension (PaO2) will be normal. The only abnormality on an ABG may be metabolic acidosis, which is a consequence of inadequate oxygen delivery to the peripheral tissues, resulting an anaerobic metabolism and lactic acid production. If CO poisoning is suspected, one must order a CO level or a test called co-oximetry. Co-oximetry is done routinely in some blood gas analyzers, but most do not, so this must be specifically ordered. Co-oximetry is capable of measuring the true oxygen saturation percentage and the percentage of nonfunctional hemoglobins such as carboxyhemoglobin and methemoglobin. The treatment for CO poisoning is 100 % oxygen, but if the CO level is very high, or if the victim is pregnant, hyperbaric oxygen is indicated to more effectively displace the CO from the hemoglobin.  Hyperbaric oxygen therapy is used to increase the amount of oxygen dissolved in the plasma, by increasing the ambient pressure.

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CO is synthesized naturally in the body and serves a range of physiological functions including vasodilation, angiogenesis, vascular remodeling, protection against tissue damage and modulation of the inflammatory response. Approximately 85% of the CO is produced by heme oxygenase (HO), which catalyses heme to CO, iron and biliverdin. Biliverdin is further broken down into bilirubin. The major site of heme catabolism, and thus CO production, is the liver. The normal blood COHb saturation in non-smokers is approximately 1%, the mean saturation in smokers of approximately 20 cigarettes per day lies around 5.5%. The majority of CO is removed from the body via expiration.

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Common CO Poisoning Sources:

Faulty furnaces, heaters

Auto exhaust

Gas generators

Charcoal grills used indoor

Tobacco smoke

Fires

Small gas engines or equipment

Gas appliances

Gas heaters in enclosed area

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Carbon Monoxide and SpCO% Measurement:

0 – 5%

Considered normal in non-smokers. When > 3% with symptoms, consider high flow oxygen and evaluate environment for CO sources. Consider measuring others in same room/office/vehicle as patient. In absence of symptoms, no further medical evaluation of SpCO needed.

5 – 10%

Considered normal in smokers, abnormal in non-smokers. If symptoms are present, consider high flow oxygen and inquire if others are ill. Alert Fire Department.

10 – 15%

Abnormal in any patient. Assess for symptoms, consider high flow oxygen. Evaluate environment for CO sources.

> 15%

Significantly abnormal in any patient. Administer high flow oxygen, assess for symptoms, consider transport. Evaluate environment for CO sources.

> 30%

Consider transport to hyperbaric facility (some experts recommend hyperbaric referral for any patient > 25% or with altered mental status or pregnant).

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Confirmation of the pulse oximetry gap in carbon monoxide poisoning: a 1997 study.

Study was conducted to demonstrate the degree to which pulse oximetry overestimates actual oxyhemoglobin (O2Hb) saturation in patients with carbon monoxide (CO) poisoning.  There is a linear decline in O2Hb saturation as COHb saturation increases. This decline is not detected by pulse oximetry, which therefore overestimates O2Hb saturation in patients with increased COHb levels. The pulse oximetry gap increases with higher levels of COHb and approximates the COHb level. In patients with possible CO poisoning, pulse oximetry must be considered unreliable and interpreted with caution until the COHb level has been measured.

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Pulse oximetry correction for smokers: a 1996 study.

Pulse oximetry oxygen saturation (SpO2) does not distinguish carboxyhemoglobin (COHb) from oxyhemoglobin (O2Hb), giving a false impression of the apparent degree of oxyhemoglobin saturation in smokers who have elevated levels of COHb. This pilot study suggests that smoking exposure history correlates with COHb levels and that correction for smoking exposure improves the accuracy of pulse oximetry.

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Current pulse oximeters overestimate arterial oxygenation in patients with elevated COHb. The amount of overestimation is approximately equal to the amount of COHb present. Accurate measurement of arterial oxygen saturation in patients with elevated COHb can only be performed via analysis of arterial blood with a laboratory co-oximeter or newly designed non-invasive pulse co-oximeter.

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Methaemoglobin:

Methaemoglobin is formed by oxidation of the iron moiety of haemoglobin, which changes from the normal, ferrous state (Fe++) to a ferric state (Fe+++). Methaemoglobinaemia is a clinical condition in which more than 1% of haemoglobin is oxidised to methaemoglobin. It manifests as cyanosis when levels of methaemoglobin are more than 10% (1.5 g/dl).Ferric haem is incapable of binding oxygen and causes an allosteric change in the remaining haem moieties of the molecule, which impairs the release of oxygen and shifts the oxyhemoglobin-dissociation curve to the left. Methaemoglobin is an abnormal type of haemoglobin that does not bind oxygen well. Normally 1-2% of people’s haemoglobin is methaemoglobin, a higher percentage than this can be genetic or caused by exposure to various chemicals and depending on the level can cause health problems.

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Methemoglobin is brown in color. Patients with methemoglobinemia are classically “ashen gray” in color. Their pulse oximetry value will read low, so this condition does not fool the pulse oximeter as it does in CO poisoning. Another clue is that when supplemental oxygen is given to the patient, the pulse oximetry reading does not change. It will still be low. When an arterial blood gas is drawn, the blood appears to be a chocolate brown color which is quite eye opening. The cause is usually idiopathic, but the ingestion of nitrites is one of the known causes. The condition is usually self-limited and resolves gradually with IV fluid hydration. IV methylene blue can be given for severe cases. Oxygen supplementation is somewhat helpful and PRBC transfusion can be used to increase the oxygen carrying capacity in severe cases.

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A typical ABG in CO poisoning or methemoglobinemia patients is pH 7.26, PCO2 34, PO2 100, bicarb 15, BE -11, if the patient is breathing room air. If the patient is breathing supplemental oxygen, then the ABG will be pH 7.26, PCO2 34, PO2 400, bicarb 15, BE -11 (i.e., just the PO2 goes up), although this does not change the oxygen saturation much. Although the blood gas machine will calculate that the oxygen saturation is 100%, remember that the ABG machine did not measure this, but rather it calculates this based on the assumption that the sample contains normal hemoglobin (which is not the case if the patient has CO poisoning or methemoglobinemia). The paradox is that the ABG slip will indicate that the oxygen saturation is 100%, while the co-oximetry report will indicate that the oxygen saturation is very low (e.g., 70%).  In summary, CO poisoning has a low true oxygen saturation, red color, 100% oxygen saturation on pulse oximetry (which is false), and normal PO2 on ABG. Methemoglobinemia has a low true oxygen saturation, brown color, low oxygen saturation on pulse oximetry, and normal PO2 on ABG. Clinicians need to be aware of the effect that MetHb has on pulse oximetry. As a general rule of thumb, large quantities of MetHb (> 10%) may result in a SpO2 reading of approximately 85%. Low amounts of MetHb (< 10%) will reduce a high SpO2 by approximately half the MetHb%.

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Why methaemoglobinaemia causes trouble with pulse oximetry:

The extinction coefficient of methemoglobin at 660 nm is similar to that at 940 nm, resulting in a red-to-infrared ratio of 1:1. The corresponding SpO2 value for this ratio is approximately 85 percent. Hence, as the methemoglobin level increases, the SPO2 will tend toward this value. When methemoglobin levels are in excess of 30 percent, the SpO2 will plateau at 85 percent and will be relatively unaffected by the oxygenation status.

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Finally, it should be noted that pulse oximeters are not reliable in the presence of dyshemoglobins – hemoglobins that cannot bind oxygen. The two major dyshemoglobins encountered in clinical practice are carboxyhemoglobin (COHb) and methemoglobin (MetHb). Oximeters do not differentiate hemoglobin bound to carbon monoxide from hemoglobin bound to oxygen; the machines report the sum of both values as oxyhemoglobin. In contrast to blood co-oximeters, which utilize four wavelengths of light to separate out oxyhemoglobin from reduced hemoglobin, methemoglobin and carboxyhemoglobin, pulse oximeters utilize only two wavelengths of light. As a result, pulse oximeters measure COHb and part of any MetHb along with oxyhemoglobin, and combine the three into a single reading, the SpO2. (MetHb absorbs both wavelengths of light emitted by pulse oximeters, so that SpO2 is not affected as much by MetHb as for a comparable level of COHb).Thus a patient with 80% oxyhemoglobin and 15% carboxyhemoglobin would show a pulse oximetry oxygen saturation (SpO2) of 95%, a value too high by 15%. For this reason pulse oximeters should be used cautiously (if at all) when there may be an elevated carbon monoxide level, for example in patients assessed in an emergency department. Note that excess carboxyhemoglobin is present in all cigarette and cigar smokers. A resting SpO2 should be interpreted cautiously in any outpatient who has smoked within 24 hours. The half-life of CO breathing ambient air is about 6 hours, so 24 hours after smoking cessation the CO level should be normal, i.e., less than 2.3%. If there is concern about the true SaO2, it should be measured on an arterial blood sample in co-oximeter; alternatively, the percent COHb can be measured on a venous sample, and the value subtracted from the SpO2. The spectrophotometric technique used by pulse oximeters also makes their oxygen saturation reading less reliable in the presence of excess methemoglobin (metHb). MetHb reduces the SpO2 linearly until a level of about 85%, at which point further increases in metHb do not cause further lowering of SpO2. A finding of unexpectedly low SPO2 (e.g., 91% in a patient with normal cardiorespiratory system who is receiving nasal oxygen) should make one think of excess methb; in such cases an arterial blood sample should be obtained for direct measurement of SaO2 and PaO2.

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Sulphaemoglobin contains an additional sulphur molecule compared to haemoglobin. It has no respiratory function, doesn’t alter the life-span of the red-cell and remains unchanged in the cells. Symptoms include a blueish or greenish discoloration of the blood, skin, and mucous membranes, even though a blood count test may not show any abnormalities in the blood. This discoloration is called cyanosis, and is caused by greater than 5 grams per cent of deoxyhemaglobinemia, or 1.5 grams per cent of methemaglobinemia, or 0.5 grams per cent of sulphemaglobinemia, all serious medical abnormalities. Increases are associated with antimony compounds, acetanalide and phenacetin medication (compounds related to paracetamol), sulphonamide therapy, nitro-glycerine poisoning and ingestion of bromide, nitrate (often in impure ground water), sulphur, sulphides and thiosulphate. These substances may cause damage to the red-cell enzymes or there may be an association with the formation of hydrogen sulphide in the bowel. The condition generally resolves itself with erythrocyte (red blood cell) turnover, although blood transfusions can be necessary in extreme cases.

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Oxygen concentration in blood can be measured as functional saturation or fractional saturation. Commercial pulse oximeters display functional saturation which takes into account two species of hemoglobin, oxyhemoglobin (O2Hb) and deoxyhemoglobin, also called reduced hemoglobin (Hb). Simply put, functional saturation is the amount of oxygenated blood compared to deoxygenated blood. A laboratory Co-oximeter, which utilizes four or more wavelengths of light instead of two, is capable of measuring both functional saturation and fractional saturation, a more specific and accurate measurement of blood oxygenation. Fractional saturation takes into account all common species of hemoglobin: O2Hb, deoxyHb, methemoglobin (MetHb) and carboxyhemoglobin (COHb). In most clinical situations, when it can be assumed that MetHb and COHb levels are normal, functional saturation is adequate for determining a patient’s respiratory status and pulse oximetry can be used to monitor the patient. However when MetHb or COHb levels of the patient are outside the normal ranges they can interfere with the accurate reading of oxygenated hemoglobin by pulse oximetry. In these cases, Co-oximetry is needed to monitor the patient’s true respiratory status. The most widely accepted method for determining the accuracy of pulse oximetry readings is a direct comparison with functional arterial saturation readings (SaO2) from a laboratory Co-oximeter. This comparison has routinely been reported in the literature in the terms of bias and precision.

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Case-1

A 54-year-old man came to the emergency room (ER) complaining of headaches and shortness of breath. On room air his PaO2 was 89 mm Hg, PaCO2 38 mm Hg, pH 7.43; hematocrit was 44%. SaO2 was not directly measured but instead calculated at 98% for this PaO2, based on a standard oxygen dissociation curve. After some improvement he was scheduled for a brain CT scan two days later, and discharged from the ER. He was brought back to the ER the next evening, unconscious. Ambulance attendants alerted the ER physician to a possible faulty heater in the patient’s house. This time carbon monoxide and SaO2 were measured along with routine arterial blood gases. The results: PaO2 79 mm Hg, PaCO2 31 mm Hg, pH 7.36, SaO2 53%, carboxyhemoglobin 46%. This patient’s true SaO2 would have been much lower than 98% had it been measured on the first ER visit instead of just calculated. The physician missed hypoxemia as a cause of headache and dyspnea because of the ‘normal’ calculated SaO2. Carbon monoxide by itself does not affect PaO2 but only SaO2 and O2 content. (Slight reduction in PaO2 on the patient’s second visit was attributed to some basilar atelectasis and resulting V-Q imbalance).  Confusion about interpretation of oxygen saturation in the presence of excess CO is not unusual and even finds its way into peer-review literature. To know the oxygen content one needs to know the hemoglobin content and the SaO2; both should be measured as part of each arterial blood gas test. As shown above, a calculated SaO2 may be way off the mark and can be clinically misleading. This is true even without excess CO in the blood. One study of over 10000 arterial samples found wide variation in measured SaO2 for a given PaO2; for example, in the PaO2 range of 56-64 mm Hg the measured SaO2 ranged from 69.7 percent to 99.4 percent.

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Case-2

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Oxygen saturation (SO2) can be measured by three approaches that are often used interchangeably, although the measured systems are quite different. Pulse oximetry is a noninvasive, spectrophotometric method to determine arterial oxygen saturation. Co-oximetry is a more complex and reliable method that measures the concentration of hemoglobin derivatives in the blood from which various quantities such as hemoglobin derivative fractions, total hemoglobin, and saturation are calculated. Blood gas instruments calculate the estimated O2 saturation from empirical equations using pH and PO2 values. In most patients, the results from these methods will be virtually identical, but in cases of increased dyshemoglobin fractions, including methemoglobinemia, it is crucial that the distinctions and limitations of these methods be understood.

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Diabetes mellitus:

Pulse Oximetry may be affected by other Abnormal Hemoglobin:

Glycosylated Hemoglobin A1c levels >7% in type 2 diabetics with poor glucose control have been shown to result in overestimation of oxygen saturation as assessed by pulse oximetry.

Pulse oximetry not reliable for diabetic patients? A 2012 study.

According to the results of a recent clinical study, pulse oximetry may not be suitable for assessment of blood oxygenation among type 2 diabetic patients with poor glycemic control and consequent increased HbA1c. The study population comprised 261 type 2 diabetes patients who were critically ill and required oxygen therapy and/or mechanical ventilation. Their care included continuous monitoring of oxygen saturation using a pulse oximeter. Fasting blood was sampled from each study patient for glucose and HbA1c. Arterial blood was sampled for blood gas analysis, including measurement of SaO2. As arterial blood was sampled, the patient’s SpO2 reading from pulse oximeter was recorded. For the purposes of this study poor glycemic control was defined as HbA1c > 7.0 %; by this definition 114 of the 261 patients (44 %) had poor glycemic control. There was essentially no difference between SpO2 and SaO2 among those with adequate glycemic control: mean SpO2 95.1 % ± 2.8 and mean SaO2 95.3 % ± 2.8. However, there was a significant difference (bias) between the two parameters among those with poor glycemic control: mean SpO2 98.0 % ± 2.6 and mean SaO2 96.2 % ± 2.9. The magnitude of the bias was demonstrated to correlate with HbA1c, so that the higher the HbA1c the greater is the difference between SPO2 and SaO2. The authors were able to conclude that among patients with poorly controlled type 2 diabetes, pulse oximetry overestimates arterial oxygen saturation. It may be more appropriate to use arterial blood gas analysis, rather than pulse oximetry, to monitor treatment of hypoxemia in these patients.

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Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults: 1998:

There were a total of 169 oximeter trials on 41 oximeter models from 25 different manufacturers. Studies were conducted in various settings with a variety of subjects, with most being healthy adult volunteers. Pulse oximeters were found to be accurate within 2% (± 1 SD) or 5% (± 2 SD) of in vitro oximetry in the range of 70% to 100% SaO2. In comparing ear and finger probes, readings from finger probes were more accurate. Pulse oximeters may fail to record accurately the true SaO2 during severe or rapid desaturation, hypotension, hypothermia, dyshemoglobinemia, and low perfusion states.

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Falsely high or falsely low SpO2 reading:

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No effect on SpO2:

Fetal haemoglobin (HbF), Bilirubin (absorption peaks are 460, 560 and 600 nm), dark skin.

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Cyanide poisoning gives a high reading, because it reduces oxygen extraction from arterial blood. In this case, the reading is not false, as arterial blood oxygen is indeed high in early cyanide poisoning.

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Response to errors in pulse oximetry:

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Synopsis of pulse oximetry limitations:

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Patients who need Oxygen regardless of Oxygen Saturation Measurement:

1 Patients in cardiac or respiratory arrest

2 Patients with chest pain suspected to be of cardiac origin

3 Patients with multisystem trauma

4 Patients who are apnoeic or who require assisted ventilation

5 Patients with suspected or confirmed carbon monoxide poisoning or smoke inhalation

6 Neonatal patients in distress

7 Patients with suspected sickle cell crisis

8 Hypotensive patients (SBP < 80 mm Hg)

9 Near drowning patients

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Pulse oximetry vs. ABG:

Pulse oximeters give non-invasive estimation of the arterial haemoglobin oxygen saturation. The gold standard for measurement of oxygen saturation remains arterial blood gas (ABG) analysis with co-oximetry. However, this is invasive, painful, time consuming, costly, provides only intermittent information on patient status, and is impractical in most primary care settings.

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Speed:

•Pulse oximetry measures a patient’s arterial saturation of oxygen (SpO2) in seconds; measurements obtained from arterial blood gases (ABG) can take several minutes to acquire and are usually drawn by a respiratory therapist, transported to the blood gas lab, measured and finally reported back to the doctor. The information from an ABG analysis provides for more information than just the oxygen level and is essential in emergencies, but oximetry is equally important to ensure the patient does not suffer the effects of hypoxia unnecessarily.

Accurate and Easy to Use:

•While not as precise as an ABG measurement, pulse oximeters are accurate with most patients, especially in emergency situations where seconds matter; however, it should not be used indiscriminately for some chronic conditions, such as chronic obstructive pulmonary disease (COPD), in which a patient may have chronically low oxygen levels and raising them too high can be dangerous. Little to no training is needed to perform pulse oximetry. Most oximeters have only one button and as long as the probe is placed properly, virtually anyone can use it. In their infancy, oximeters were the size of old cassette recorders and just as cumbersome. The newest generation of oximeters is streamlined, rugged and even easier to use. Furthermore, they are now available for home use.

Non-Invasive and Reliable:

•ABG measurements, though exact, require blood drawn from an artery, which can lead to complications ranging from hematoma to laceration of the artery. Pulse oximetry is performed on a fingertip and measures through the nail bed. As long as the oximeter is used properly and is calibrated regularly, it is easy to use and usually reliable. Good peripheral circulation in the patient’s extremities is critical to obtaining accurate readings and most oximeters on the market incorporate a perfusion gauge, usually in LED bar lights, that shows the strength of the patient’s peripheral circulation. When a strong pulse is not present in the hands or feet, readings can be made with a special adhesive probe placed on the patient’s earlobe or even the bridge of the nose.

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Contraindication to ABG:

1. Bleeding diathesis

2. AV fistula

3. Severe peripheral vascular disease, absence of an arterial pulse

4. Infection over site

Obviously pulse oximetry or pulse co-oximetry or pulse oximetry with capnography are only alternatives when ABG is contraindicated.

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Why ABG instead of SpO2:

1. Pulse oximetry does not assess ventilation (PCO2) or acid base status.

2. Pulse oximetry becomes unreliable when saturations fall below 70-80%.

3. Technical sources of error (ambient or fluorescent light, hypoperfusion, nail polish, skin pigmentation)

4. Pulse oximetry cannot interpret methemoglobin or carboxyhemoglobin.

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The patient’s pulse oximetry reading is SpO2 98% on air. PaO2 23mm and SaO2 38 % on ABG.

What are the possible explanations for the discrepancy between the pulse oximetry reading and the oxygen saturation on the arterial blood gas?

Possible explanations for ‘pseudo-hypoxaemia’ include:

1. Equipment failure

— faulty pulse oximeter

— faulty blood gas analyser

2. Blood sample used was actually venous in ABG

3. Blood sample taken from a site affected by localised hypoxemia, e.g. ischaemic limb

4. Excessive oxygen consumption following blood sample collection (e.g. massive leukocytosis or thrombocytosis)

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Arterial puncture or pulse oximetry?

Arterial puncture is the general accepted standard method for monitoring oxygen therapy in critically ill patients, but this technique is painful for the patient, has the potential of complications, and does not provide immediate continuous data. Pulse oximetry is a non-invasive method used to measure arterial oxygen saturation with a clinically acceptable accuracy of +/- 2%. Despite some limitations, pulse oximetry is considered to be reliable in most cases in detecting hypoxaemia and monitoring oxygen therapy in stationary units. The pulse oximeter can reduce the number of arterial punctures, personnel’s time consumption, and limit oxygen abuse. Furthermore the new transportable and hand-held pulse oximeters offer new possibilities for continuous 24 hour monitoring of oxygen saturation also out of hospitals. The pulse oximeter can optimize monitoring patients’ oxygen saturation in the stationary units, however, arterial puncture will remain the most reliable method in the assessment of hypoxaemia and hypercapnia, especially in acute situations.

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A comparison of Arterial Oxygen Saturation measured both by Pulse Oximeter and Arterial Blood Gas Analyzer in Hypoxemic and Non-hypoxemic Pulmonary Diseases: a 2006 study:

The purpose of this study was to determine the correlation between SpO2 and arterial O2 saturation measured with blood gas analyzer (SaO2) in hypoxemic and non-hypoxemic patients. Hypoxemia was considered as SpO2<90%. In pulmonary diseases with SpO2 ≥ 80%, pulse oximetry has high accuracy in estimating SaO2 and may be used instead of arterial blood gases (ABG). In patients with SpO2 < 80%, however, the exact estimation of SaO2 and the evaluation of oxygenation by pulse oximeter is not a good substitution for ABG analyzer.

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Pulse oximetry versus arterial blood gas specimens in long-term oxygen therapy (LTOT):

Portable pulse oximeters are now widely available for the assessment of arterial oxygenation, and the U.S. Medicare program considers saturation readings to be acceptable substitutes for arterial PO2 in selecting patients for long-term oxygen therapy (LTOT). Current oximeters are reasonably accurate (plus or minus 2 or 3 percent of the co-oximetry value), but the clinician should be aware of several potential problems. Readings may be inaccurate in the presence of hemodynamic instability, carboxyhemoglobinemia, or dark skin pigmentation, and also during exercise. Indicated saturation may substantially overestimate arterial PO2 if the patient is alkalemic. Pulse oximetry cannot detect hypercapnia or acidosis. For these and other reasons, pulse oximetry should not be used in initial selection of patients for LTOT, as a substitute for arterial blood gas analysis in the evaluation of patients with undiagnosed respiratory disease, during formal cardiopulmonary exercise testing, or in the presence of an acute exacerbation. Pulse oximetry is an important addition to the clinician’s armamentarium, however, for titrating oxygen dose in stable patients, in assessing patients for desaturation during exercise, for sleep studies, and for in-home monitoring.

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Pros and cons of pulse oximetry:

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The advantages of the pulse oximeter could be listed as follows:

• Affordable Price: almost all pulse oximeter are at quite an affordable price in the market.

• Fast: Provides real-time, absolute measurement of oxygen levels without the use of empirical tables.

• Versatile: it can be used virtually anywhere – hospital or home – to determine oxygen levels.

• Accurate: the pulse oximeter provides a relatively accurate measure which could be taken into account for a proper diagnosis

• Extended use: The patient mobility makes this technology suitable for long-term patient monitoring.

• Noninvasive sampling: The accuracy of this technology allows doctors, clinics and hospitals to replace traditional invasive sampling procedures, such as arterial puncture or an indwelling arterial catheter, for obtaining absolute oxygen measurement.

• Ease of use: Does not require preliminary calibration.

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Advantages:

A pulse oximeter is useful in any setting where a patient’s oxygenation is unstable, including intensive care, operating, recovery, emergency and hospital ward settings, pilots in unpressurized aircraft, for assessment of any patient’s oxygenation, and determining the effectiveness of or need for supplemental oxygen. Assessing a patient’s need for oxygen is the most essential element to life; no human life thrives in the absence of oxygen (cellular or gross).  Because of their simplicity and speed, pulse oximeters are of critical importance in emergency medicine and are also very useful for patients with respiratory or cardiac problems, especially COPD, or for diagnosis of some sleep disorders such as apnea and hypopnea. Portable battery-operated pulse oximeters are useful for pilots operating in a non-pressurized aircraft above 10,000 feet (12,500 feet in the US) where supplemental oxygen is required. Prior to the oximeter’s invention, many complicated blood tests needed to be performed. Portable pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise. Some portable pulse oximeters employ software that charts a patient’s blood oxygen and pulse, serving as a reminder to check blood oxygen levels.

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Pulse oximetry’s advantages over arterial blood gases measurements are obvious: noninvasive, less pain and risk than arterial puncture, less expensive, more real-time or point-of-care testing method (immediately available vs time for obtaining/ transporting/ running/reporting a blood gas), and a continuous monitor (rather than an isolated points in time). The advantages of pulse oximetry include use as a continuous noninvasive marker or warning signal for adverse patient events that can result in hypoxia/arterial desaturation. By detecting those events early, treatment can be initiated sooner with the goal of improving patient outcomes. Because clinical detection of cyanosis is unreliable, use of pulse oximetry should allow earlier detection of hypoxemia.  Reports from the recovery room and the operating room do indicate a faster detection of hypoxic episodes, a lower incidence and shorter duration of arterial desaturation, and fewer adverse events in the recovery room in cases where pulse oximetry is used.  However, several studies of pulse oximetry in anesthesia/post anesthesia care and in general care units failed to show a difference in patient outcome with its use. The consensus and expert opinion are that pulse oximetry can and should be used, and there are many clinical indications for its use.

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Pulse oximetry is easy to use and requires no special training. It can be applied easily and quickly and is inexpensive. It is small, lightweight, and portable; therefore, it can be used in almost any area and requires little space. It can be stand-alone equipment or incorporated into a bedside monitoring unit. It can be used in any age or type of patient from newborns to geriatric patients, in the ED, intensive care units, inpatient floors, operating suite, recovery room, and in prehospital care. It has become the fifth vital sign and is a standard of care during procedures requiring general anesthesia and during procedural sedation and analgesia.

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The cons of using Pulse Oximetry:

Like any medical device, pulse oximeters have their downside. Patients are cautioned to use common sense when using a pulse oximeter at home and not to rely, solely, on an oxygen saturation reading as an indicator that something is medically wrong. Moreover, before purchasing a home pulse oximeter, you should understand that they:

•may provide a false reading; for example, a COPD patient can be severely short of breath, but their oxygen saturation reading may be near normal.

•may be ineffective in the presence of certain conditions, including cardiac or respiratory arrest, cardiac arrhythmias, shock, carbon monoxide poisoning, conditions that cause poor circulation or poor perfusion to the tissues, arteriovenous fistulas, cold extremities, edema, black, green or blue nail polish, tremors, shivering, rigor or muscle twitching.

•may lag behind a patient’s condition; for example, the blood oxygen level (PaO2) could potentially decrease to a critical level before the decreased SpO2 (oxygen saturation reading) is displayed on the monitor.

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Warnings of using pulse oximeter:

• One of the greatest draw back would be although a pulse oximeter is used to monitor oxygenation; it cannot determine the metabolism of oxygen, or the amount of oxygen being used by a patient. For this purpose, it is necessary to also measure carbon dioxide (CO2) levels.

• The pulse oximeter also fails to function properly when there is a reduction of peripheral blood flow as in peripheral vasoconstriction, severe hypotension, cold, cardiac failure, some cardiac arrhythmia and peripheral vascular diseases. This is due to inadequate signal for analysis.

• Venous congestion due to tricuspid regurgitation and various systemic abnormal pulsations can produce low reading.

• Bright overhead lights in surgical rooms and shivering can cause an error in the reading.

• Another huge problem would be the inability to distinguish between different forms of hemoglobin as in methemoglobin and carboxyhemoglobin where low saturations of hemoglobin with oxygen due to the presence of these other forms can bring about a false high saturation value.

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Pitfalls of SpO2:

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Pulse oximetry is noninvasive and considered safe, although rare reports of pressure necrosis and burns due to defective probes have been reported.  Pulse oximetry probes can be a source of nosocomial infection if they become contaminated with pathogenic bacteria. However, there are many methods to avoid this possibility.  Disposable probes can be resterilized, and protective sheaths can be placed on the probe to allow for multiple uses. Pulse oximetry has a low failure rate. In one operating room study, the failure rate was less than 5% with a trend toward failure occurring in elderly and sicker patients and during longer surgical procedures. Accidental disconnection or probe misplacement are probably the most common causes of pulse oximetry failure.

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Contraindications to pulse oximetry:

Pulse oximetry monitoring should not be used

1. during CPR

2. when patient is hypovolemic

3. for assessing adequacy of ventilator support

4. for detecting worsening of lung function in patients on high concentration of oxygen

These conditions all require blood gas analysis and other laboratory tests for diagnosis and monitoring.

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A pulse oximeter should never be used during a cardiac arrest situation because of the extreme limitations of blood flow during cardiopulmonary resuscitation and the pharmacological action of vasoactive agents administered during the resuscitation effort.

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Look at the Whole Clinical Picture:

There are other pitfalls of oximetry as well. Caregivers must always verify results by looking at the whole clinical picture. A patient’s skin pallor, presence of cyanosis and other factors can belie or substantiate a pulse oximeter reading. Also, since cyanosis of nail beds can be due to poor circulation, the oral mucosa should be checked for color and/or presence of cyanosis. In certain instances, such as the smoke inhalation, an arterial blood gas with co-oximetry may be needed. This will give actual SaO2 and carboxyhemoglobin levels.  Even accurate oximeter readings must be used as part of the total assessment. For example, a patient with acute change in his level of consciousness. His pulse oximeter reading may be over 90 percent, and yet, to dismiss a possible respiratory reason for the change in consciousness may be in error, since an increase in carbon dioxide in the blood can cause this change and will not necessarily be picked up by oximetry. Patients with chronic obstructive pulmonary disease can have a reasonable saturation and yet be retaining carbon dioxide, resulting in an acute change consciousness. The use of a pulse oximeter to detect hypoventilation is impaired with the use of supplemental oxygen, as it is only when patients breathe room air that abnormalities in respiratory function can be detected reliably with its use. Therefore, the routine administration of supplemental oxygen may be unwarranted if the patient is able to maintain adequate oxygenation in room air, since it can result in hypoventilation going undetected. Pulse oximetry is an excellent tool as long as care is taken to not depend entirely on this technology in the absence of correlating clinical information.

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Oxygenation vs. Ventilation:

Ventilation, which can be spontaneous (as in breathing) or artificial (as in mechanical ventilation) is the movement of air in and out lungs. Both PaO2 and PaCO2 are affected by ventilation. During hypoventilation at room air, PaCO2 will rise and PaO2 will be reduced as less air brings less oxygen and takes away less carbon dioxide. Perfusion is amount of blood flowing in lung capillaries for gas exchange. The blood will exchange oxygen and carbon dioxide at alveolar-capillary membrane with alveolar air. If perfusion is reduced for example due to massive pulmonary embolism, less blood will be available to alveolar air, less blood will be oxygenated and PaO2 and SaO2 will fall. However, PaCO2 will not rise because of high solubility and high diffusing capacity of carbon dioxide compared to oxygen. So CO2 will be exhaled in sufficient quantity despite poor perfusion as long as ventilation is good. In fact hypoxemia induced hyperventilation would wash away CO2 and PaCO2 may be lower (hypocapnia). Additionally, every minute we inhale net 250 ml O2 and exhale net 25 ml CO2 as majority of CO2 produced is converted into H2CO3 to be used in acid-base balance. So this 25 ml CO2 with high diffusing capacity can be removed easily. In other words, oxygenation requires good perfusion and good ventilation while carbon dioxide removal needs good ventilation alone. In other words, carbon dioxide level can be used to judge adequacy of ventilation.

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Oxygenation refers to the amount of oxygen in a medium. In blood it may be taken to be synonymous with saturation, which describes the degree to which the oxygen-carrying capacity of haemoglobin is utilised, normally 98-100%.   PaO2 is affected by supplemental oxygen. If you give supplemental oxygen to a patient, you will see PaO2 rise but PaCO2 unaffected. So PaO2/SpO2 measures oxygenation.  A complete respiratory assessment of at-risk patients must include assessment of both oxygenation and CO2 removal i.e. ventilation. Oxygenation—how well oxygen is moving across the alveolar-capillary membrane and into the blood to be carried to tissue—can be determined by analyzing a patient’s partial oxygen pressure (PaO2) and SpO2 (or SaO2). Ventilation (how well a patient can exhale carbon dioxide produced by metabolic activities) can be determined by analyzing a patient’s partial carbon dioxide pressure (PaCO2), and the partial pressure of carbon dioxide in exhaled gas—the end-tidal CO2 (EtCO2). Pulse oximetry estimates oxygenation. Capnography estimates ventilation.

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What pulse oximetry can’t tell you?

Pulse oximetry is a useful tool for assessing oxygen saturation (oxygenation), but it doesn’t provide a complete picture of your patient’s respiratory status. Understanding what pulse oximetry can and can’t do will help you to use this technology wisely. Pulse oximetry is a noninvasive method of monitoring a patient’s pulse rate and arterial oxygen saturation. A pulse oximeter uses a light-emitting diode (LED) and a photodetector to estimate the percentage of total hemoglobin that’s saturated (filled) with oxygen molecules, based on the amounts of red and infrared light that pass through the vascular bed. Arterial oxygen saturation is represented by the symbol SpO2 when measured by pulse oximetry or SaO2 when measured by co-oximetry. For a healthy patient, an SpO2 of 95% – 100% is generally considered normal. Pulse oximetry is now a part of routine perioperative monitoring, and is widely used to monitor patients in many different settings, including the ED, OR, ICU, PACU, and med/surg units. However, because it doesn’t provide any information about a patient’s ventilation, relying on pulse oximetry alone could compromise patient safety, particularly in patients who are receiving supplemental oxygen or who are at risk of respiratory depression. Yet, a recent study found that only 35% of nurses (and 39% of physicians) in a major medical center knew that pulse oximetry monitored oxygen saturation only and did not reflect changes in ventilation. The study also found that an educational program significantly improved clinicians’ knowledge of pulse oximetry. Pulse oximetry is a valuable tool, but it’s only one part of a complete assessment of a patient’s respiratory status. To be most effective, it must be used properly, and in conjunction with other methods of respiratory monitoring. By understanding the uses and limitations of pulse oximetry, you’ll be able to better assess and care for your patients. Pulse oximetry can tell you about saturation only; to assess other measures of oxygenation and ventilation, you need to consider ABG analysis and capnography (which will be discussed below). In some cases, acceptable pulse oximetry readings (“good sats”) have falsely reassured clinicians despite serious deterioration in a patient’s respiratory status as shown by dangerously high levels of PaCO2. I would emphasize that measurements of carbon dioxide (CO2) and acid–base balance are also critical in the care of patients with respiratory disorders or unbalanced pH and that these disorders cannot be evaluated with the use of pulse oximetry. In particular, a normal pulse oximetry measurement does not exclude important abnormalities in the partial pressure of arterial carbon dioxide (PaCO2) or pH. Therefore, serious elevations in the PaCO2, which are indicative of ventilatory dysfunction, can be present when the results of pulse oximetry are normal.  Pulse oximetry is an excellent oxygenation monitor, but it does not alert the clinician to changes in ventilation in a timely manner, particularly when supplemental oxygen is used. Anesthesiologists are well aware of this limitation of pulse oximetry and recommend the use of capnography to monitor ventilation during procedural sedation.

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Taking a more comprehensive approach to respiratory monitoring is especially important for patients at increased risk of respiratory depression, which can be precipitated by:

• altered level of consciousness due to sedation, medications such as opioids, or other conditions;

• decreased blood flow to the brain’s respiratory centers as the result of increased intracranial pressure, shock, or other factors;

• fatigue associated with the increased work of breathing;

• cardiac or pulmonary diseases that affect oxygenation.

At-risk patients may need not only pulse oximetry but also ABG analysis or capnography. ABG analysis provides a more complete picture of a patient’s respiratory status, including PaO2, PaCO2, arterial pH, and acid-base balance, but it requires a sample of arterial blood and takes time to receive the results.

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Alveolar hypoventilation is the main form of respiratory failure postoperatively and results from combinations of central respiratory depression, muscular weakness, and upper airways obstruction. As arterial carbon dioxide tension rises so does alveolar carbon dioxide tension (PCO2) because CO2 diffuses rapidly across alveolar capillary membrane; concurrently alveolar PO2 falls, leading to arterial hypoxaemia. If the patient is breathing room air then the saturation will fall early and is a reasonably sensitive indicator of hypoventilation. The situation is different if the patient is receiving supplemental oxygen. The alveolar PO2 will now be much higher and consequently higher PaO2 will raise SpO2.The failure to detect hypoventilation in such a patient is not a failure of pulse oximetry as such but an example of a false sense of security generated by a single physiological variable being within safe limits. The same caveat applies to the use of pulse oximetry to detect hypoventilation under anaesthesia, when patients routinely receive high fractional inspired oxygen concentrations. Although pulse oximetry may be “the most significant technological advance ever made in the monitoring of the well-being and safety of patients during anaesthesia, recovery and critical care,”‘  it must be understood that a normal reading of saturation in the presence of an increased inspired oxygen concentration gives no information about the adequacy of ventilation. Falls in saturation under these circumstances will occur late and are non-diagnostic. Under no circumstances should the pulse oximeter be relied on as the sole monitor to detect such events as oesophageal intubation, cardiac arrest, breathing system disconnections, or failure of the oxygen supply.

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Although the physiologic consequences of moderate hypoventilation have not been clearly elucidated, profound hypoventilation with the development of carbon dioxide narcosis can cause coma, respiratory arrest, and circulatory failure.  Various studies have reported the difficulty in detecting hypoventilation in patients undergoing sedation for GI, dental, and other endoscopic procedures. Moreover, several reports have discussed the failure to diagnose severe hypoventilation in the perioperative period.

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Historically, an SpO2 90% has been used to define “arterial hypoxemia.”  Accordingly, clinicians often will administer supplemental oxygen out of habit to ensure “adequate” oxygenation and to avoid reaching the 90% threshold.  But is this clinical practice warranted? Currently, there is no consensus in the literature regarding recommendations on the prophylactic administration of supplemental oxygen to all postoperative patients, and some communications have stressed the dangers of masking severe hypoventilation with supplemental oxygen. It is suggested that the decision to administer supplemental oxygen not be based on routine, but should entail consideration of the risk of masking undetected hypoventilation. One must determine whether lower SpO2 indicate hypoventilation, or mismatching of ventilation and perfusion. Then, appropriate treatment may be administered. Sedation may cause profound respiratory depression and hypoventilation. Thus, accurate monitoring of ventilatory status of sedated patients is desirable. Methods to detect hypoventilation in the spontaneously breathing patients receiving respiratory depressant drugs are limited. Pulse oximetry primarily has been used to assess oxygenation, but not ventilation. A decline in SpO2 during room-air breathing appears to be a reliable indicator of ventilator abnormalities, whether occurring at a global or regional level; the presence of such abnormalities will go undetected in the presence of supplemental oxygen. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilation in the absence of supplemental inspired oxygen.

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Supplemental Oxygen impairs detection of Hypoventilation by Pulse Oximetry: a 2004 study:

Study objective: This two-part study was designed to determine the effect of supplemental oxygen on the detection of hypoventilation, evidenced by a decline in oxygen saturation (SPO2) with pulse oximetry.

Design: Phase 1 was a prospective, patient-controlled, clinical trial. Phase 2 was a prospective, randomized, clinical trial.

Setting: Phase 1 took place in the operating room. Phase 2 took place in the postanesthesia care unit (PACU).

Patients: In phase 1, 45 patients underwent abdominal, gynecologic, urologic, and lowerextremity vascular operations. In phase 2, 288 patients were recovering from anesthesia.

Interventions: In phase 1, modelling of deliberate hypoventilation entailed decreasing by 50% the minute ventilation of patients receiving general anaesthesia. Patients breathing a fraction of inspired oxygen (FIO2) of 0.21 (n  25) underwent hypoventilation for up to 5 min. Patients with an FIO2 of 0.25 (n  10) or 0.30 (n  10) underwent hypoventilation for 10 min. In phase 2, spontaneously breathing patients were randomized to breathe room air (n  155) or to receive supplemental oxygen (n  133) on arrival in the PACU.

Measurements and results: In phase 1, end-tidal carbon dioxide and SPO2 were measured during deliberate hypoventilation. A decrease in SpO2 occurred only in patients who breathed room air. No decline occurred in patients with FIO2 levels of 0.25 and 0.30. In phase 2, SpO2 was recorded every min for up to 40 min in the PACU. Arterial desaturation (SpO2 < 90%) was fourfold higher in patients who breathed room air than in patients who breathed supplemental oxygen (9.0% vs 2.3%, p  0.02).

Conclusion: Hypoventilation can be detected reliably by pulse oximetry only when patients breathe room air. In patients with spontaneous ventilation, supplemental oxygen often masked the ability to detect abnormalities in respiratory function in the PACU. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilator abnormalities, but only in the absence of supplemental inspired oxygen.

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The efficacy of lung function is evaluated primarily by arterial blood gas analysis. If PaO2 and PaCO2 are within normal limits, then lung function is normal. Many medical decisions, such as whether or not to administer supplementary oxygen in the hospital, prescribe home oxygen therapy, initiate noninvasive ventilation, or initiate mechanical ventilation or wean the patient from it, etc., are based on the interpretation of arterial blood gas values. Some of these decisions, which must be taken more and more often in recent years, have important personal, social, and economic repercussions. Technical innovations have made the equipment used for analyzing gases simpler and easier to handle. It is in this context oxyhemoglobin assessment through pulse oximetry (SpO2) and with the continuous, indirect estimation of PaCO2 by way of end-tidal carbon dioxide pressure (EtCO2) using capnography are discussed.

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Capnography vis-à-vis pulse oximetry:

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Capnography:

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO2) in the respiratory gases. Its main development has been as a monitoring tool for use during anaesthesia and intensive care. Capnography is a form of noninvasive monitoring of the end-tidal carbon dioxide (EtCO2) levels in the patient’s breath. By tracking the carbon dioxide in a patient’s exhaled breath, capnography enables paramedics to objectively evaluate a patient’s ventilatory status (and indirectly circulatory and metabolic status), as the medics utilize their clinical judgement to assess and treat their patients.  It is usually presented as a graph of expiratory CO2 (measured in millimeters of mercury, “mmHg”) plotted against time, or, less commonly, but more usefully, expired volume. The plot may also show the inspired CO2, which is of interest when rebreathing systems are being used. The capnogram is a direct monitor of the inhaled and exhaled concentration or partial pressure of CO2, and an indirect monitor of the CO2 partial pressure in the arterial blood. In healthy individuals, the difference between arterial blood and expired gas CO2 partial pressures is very small. In the presence of most forms of lung disease, and some forms of congenital heart disease (the cyanotic lesions) the difference between arterial blood and expired gas increases and can exceed 1 kPa. Capnographs usually work on the principle that CO2 absorbs infrared radiation. A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of CO2 in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit. The analysis is rapid and accurate. Capnography refers to a unit that displays both a numeric EtCO2 value and a CO2 waveform (capnogram). Capnography provides a graphic representation (a capnogram) of the level of exhaled carbon dioxide (CO2). The capnogram gives you breath-to-breath information about the CO2 that’s being exhaled from the lungs.

Capnography – the measurement of carbon dioxide (CO2) in exhaled breath.

Capnometer – the numeric measurement of CO2.

Capnogram – the wave form.

Capnograph – a device that measures CO2 in breath

End Tidal CO2 (EtCO2) – the level of (partial pressure of) carbon dioxide released at end of expiration.

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Capnogram:

A typical capnogram is shown in the figure below. During inspiration the CO2 tension should be neligible unless there is rebreathing. Dead space gas is exhaled first, it contains no CO2, and is followed by alveolar gas and a rapid rise in CO2 which reaches a clear plateau in normal lungs and is termed the end-tidal CO2 tension. However, if there is significant inhomogeneity of ventilation within the lungs no clear plateau is discernible and an accurate end-tidal CO2 cannot be measured. This occurs in obstructive airway disease and asthma. If tidal volumes are very small there is inadequate distinction between dead space and alveolar gas resulting in an indistinct expiratory plateau and the end-tidal CO2 tension is inaccurate.

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End-tidal CO2 (EtCO2) is the quantitative value of exhaled carbon dioxide measured from a sample source of gas obtained at the point of end-tidal exhalation. Normal values of EtCO2 are 35-45 mmHg (4.5% – 6 %), and in normal lungs, the EtCO2 approximates the arterial CO2 concentration in the blood with a value that is usually lower by 2 to 5 mmHg. Use of capnography is not limited to intubated patients; nasal cannulas and face masks can be modified to detect EtCO2. Capnography devices are now easy to use and available for patients without artificial airways; exhaled CO2 is collected from a nasal cannula-like device. Most effective way to evaluate ventilation in an alert but sedated patient is by sidestream capnography. The use of oxygen cannulas modified with an I.V. catheter that do not provide total separation on insufflated oxygen and aspirated CO2 will not produce a reliable baseline for CO2 monitoring that will be  consistent with the PaCO2.  Monitors are available for bedside use in med/surg, as part of portable monitor-defibrillators for transport, and as cartridges that can be added to the wall-mounted component of central monitoring systems in critical care areas.

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There is a simple reason capnography monitoring is increasingly becoming the standard of care during outpatient surgery procedures: it provides an immediate alarm for life-threatening breathing problems during moderate or deep sedation. Capnography monitors track end-tidal carbon dioxide (EtCO2), the concentration of carbon dioxide in exhaled air. Capnography waveforms immediately detect changes in CO2 levels that could signal respiratory distress or failure. Pulse oximeters, which had been the standard of care in outpatient surgery, take much longer to register respiratory distress. This is because oxygen levels in blood can remain normal for several minutes after a patient stops breathing.

The benefits of capnography are being recognized by professional organizations in a wide range of fields, including:

•American Association of Oral and Maxillofacial Surgeons: AAOMS Office Anesthesia Evaluations began requiring capnography in 2014 for moderate sedation, deep sedation and general anesthesia.

•Institute for Safe Medication Practices: The ISMP recommends patient-controlled analgesia procedures follow the Anesthesia Patient Safety Foundation’s guidelines on using capnography to detect unrecognized hypoventilation and carbon dioxide retention.

•American Heart Association: In 2010, the AHA began recommending the use of capnography to verify endotracheal tube placement in during triage for patients with acute coronary syndromes.

•Society of Interventional Radiology: In response to the American Society of Anesthesiologists capnography standards, the SIR recommends that interventional radiologists familiarize themselves with how capnography works and its benefits over pulse oximetry.

•Anesthesia Patient Safety Foundation: The APSF Winter 2012 Newsletter includes a four-part case study on capnography monitoring reform at St. Joseph’s/Candler Health System in Savanna, Ga.

•American Association for Accreditation of Ambulatory Surgery Facilities: The ASAASF updated its 2014 standards to include mandatory, continual end-tidal carbon dioxide monitoring to confirm correct endotracheal tube placement.

•Journal of Emergency Medical Services: A 2014 article touts the importance of prehospital airway management through the use of capnography and other monitoring techniques.

•Canadian Anesthesiologists’ Society: The CAS 2012 Guidelines were expanded to require capnography monitoring during conscious sedation and when patient airways have not been instrumented.

•Oregon Board of Dentistry: Oregon state laws were updated in 2014 to include capnography monitoring for patients under moderate sedation, deep sedation and general anesthesia. To receive permits in the above listed kinds of sedation, practices must have both capnography and pulse oximetry on site available for immediate use.

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Capnography versus Pulse Oximetry:

Capnographs and pulse oximeters present different views of the same cardiopulmonary processes.  Oximeters measure saturated hemoglobin in peripheral blood and provide additional information about the adequacy of lung perfusion and oxygen delivery to the tissues. However, pulse oximetry is a late indicator of O2 supply, and is less sensitive than capnography. Healthy patients can maintain SaO2 > 90% for minutes even with inadequate ventilation.  It does not afford a complete picture of ventilatory status.  Capnography provides an immediate picture of patient condition. Pulse oximetry is delayed. Hold your breath. Capnography will show immediate apnea, while pulse oximetry will show a high saturation for few minutes. While capnography is a direct measurement of ventilation in the lungs, it also indirectly measures metabolism and circulation. For example, an increased metabolism will increase the production of carbon dioxide increasing the EtCO2. A decrease in cardiac output will lower the delivery of carbon dioxide to the lungs decreasing the EtCO2. Accurate pulse oximetry measurement is dependent upon adequate peripheral perfusion and may be unreliable in patients who have compromised peripheral circulation. Capnography continuously and nearly instantaneously measures pulmonary ventilation and is able to rapidly detect small changes in cardio-respiratory function before oximeter readings change. Many sources recommend monitoring both SpO2 and EtCO2 on intubated and non-intubated patients.

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Which is better, pulse oximetry or waveform capnography?

The best choice depends on what we are trying to do.

If the patient is receiving paralytics during an intubation attempt, does waveform capnography matter?

No, but the pulse oximetry is important in determining how long it is safe to continue to attempt to intubate before ventilating the patient again (whether with a BVM or a crichothyrotomy). With use of preoxygenation and passive apneic oxygenation, patients may tolerate apnea for extended periods without desaturation. Apneic oxygenation dramatically changes the way we approach airway management.

Does it matter if the patient is not breathing, if the patient’s oxygen saturation is in the high 90s?

Yes, because ventilation is the removal of CO2. If the patient is already acidotic, even a brief period of apnea may kill the patient.

Does it matter if the cardiac arrest patient is receiving ventilation?

No. Chest compressions appear to provide adequate ventilation without any use of the usual means of ventilation.

Does pulse oximetry have a place in the assessment of endotracheal tube placement?

Yes, but waveform capnography is almost always the best means of tube confirmation.

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Ideally, when monitoring ventilation and oxygenation in the prehospital environment, capnography should be combined with pulse oximetry. With capnography, providers are able detect respiratory insufficiency early and are able to institute early interventions, thereby preventing arterial oxygen desaturation. However, as with any monitoring technology, the best “monitor” is the provider. Pulse oximeters and capnometers do not treat patients. Integrating the information from your monitors and clinical assessment to make sound clinical decisions is the key to successful airway management. As evidenced by the astute assessment and action of a paramedic, knowing the difference between ventilation and oxygenation is a critical concept that must be understood.

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Capnography (carbon dioxide detection) is a modality that is recommended by most anaesthesia societies, including the ASA and WFSA. It allows detection of esophageal intubation and hypoventilation nearly 100% of the time and is the monitoring modality of choice for this purpose. Yet, in resource limited settings, the benefits of capnography are less compelling than those of pulse oximetry. As Webb and colleagues have reported, pulse oximetry detects adverse events more frequently. This is presumably because pulse oximetry detects hypoxemia, which is the most common cause of death as Cooper showed nearly 20 years ago. Furthermore, increased alveolar carbon dioxide concentrations from any cause (notably hypoventilation) can be detected early with pulse oximetry if the inspired oxygen concentration is maintained at or close to that in ambient air. By contrast, early hypoxia is not readily detected with capnography. Additionally, the cost and maintenance of oximetry are generally lower than capnography. For these reasons, pulse oximetry is the preferred monitoring modality in resource-limited settings.

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Accuracy and reliability of pulse oximetry at different arterial carbon dioxide pressure levels: a 2008 study:

The present study aimed to assess whether arterial carbon dioxide pressure (PaCO2) has an impact on agreement between oxygen saturation measured with pulse oximetry (SpO2) or arterial blood gas co-oximetry (SaO2). Arterial carbon dioxide pressure status can contribute to impaired agreement between arterial oxygen saturation and arterial oxygen saturation measured with pulse oximetry, particularly in patients with hypercapnia. The main finding emerging from the present study is that PaCO2 levels can affect the accuracy and reliability of SpO2 measurements. Agreement between SaO2 and SpO2 decreases as PaCO2 increases, regardless of the grade of associated hypoxaemia. Moreover, in a large series of determinations, the present study also confirmed that SpO2 correlates poorly with SO2 when PaO2 is low, particularly when it is 54 mmHg (7.20 kPa).

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Capnography with pulse oximetry (combination):

Over the past two decades, technologies have developed to allow for rapid and continuous determination of many physiologic parameters in anesthetized and critical care patients. Two of the most important modalities are pulse oximetry and capnometry. With their use, a clinician is better equipped to ensure adequate oxygen delivery at the cellular and microcellular level and ensure a proper pH for optimal physiologic cellular function in patients. This has led to a dramatic improvement in patient safety, care and outcomes. In a study of closed claims of anesthetic-related malpractice cases, it was determined that a combination of pulse oximetry and capnography could have prevented 93% of avoidable mishaps.

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Capnography with pulse oximetry:

The Capnostream is a portable bedside monitor that continuously monitors a patient’s:

• End tidal carbon dioxide (EtCO2) – level of carbon dioxide in exhaled breath.

• Respiratory rate (RR).

• Fractional inspired carbon dioxide (FiCO2) – level of carbon dioxide present during inhalation.

• Oxygen saturation (SpO2).

• Pulse rate (PR).

The Capnostream combined capnograph/pulse oximeter monitor is intended to provide professionally trained health care providers the continuous, non-invasive measurement and monitoring of carbon dioxide concentration of the expired and inspired breath and respiration rate, and for the continuous non-invasive monitoring of functional oxygen saturation of arterial hemoglobin (SpO2 and pulse rate). It is intended for use with neonatal, pediatric and adult patients in hospitals, hospital type facilities, intra hospital moves and home environments.

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Capnostream:

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Nonin 9847 Hand Held Pulse Oximeter with CO2 Detector, Alarms & Memory:

The Nonin 9847 combines proven pulse oximetry technology with reliable CO2 detection, making it an ideal monitor for patient transport and emergency use. The Nonin 9847 Pulse Oximeter/CO2 Detector provides “first breath” activation by eliminating any warm-up time – simply turn on the power and start taking measurements.  Nonin’s patented semi-quantitative CO2 technology, combined with mainstream sampling, eliminates the need for calibration, thus reducing operating expenses.

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A single-blind study of combined pulse oximetry and capnography in children: a 1991 study.

This single-blind study examined four levels of monitoring in 402 pediatric cases. Patients were randomly assigned to one of four groups: 1) oximeter and capnograph; 2) only oximeter; 3) only capnograph; or 4) neither oximeter nor capnograph data available to the anesthesia team. An anesthesiologist, not involved in patient care, observed all cases and continuously recorded hemoglobin oxygen saturation (SpO2), ECG, expired CO2, and the oximeter plethysmographic output. Mean age, weight, ASA physical status, airway management (mask or endotracheal tube), and anesthetic technique were similar in each group. Two-hundred sixty problems were documented in 153 patients. Fifty-nine events in 43 patients resulted in “major” desaturation (SpO2 less than or equal to 85% for greater than or equal to 30 s). Fifteen “major” capnograph events (esophageal intubation, disconnection, accidental extubation, or obstructed endotracheal tube) were observed in 11 patients; 8 of these also developed varying degrees of desaturation. One-hundred thirty “minor” desaturation events (SpO2 less than or equal to 95% for greater than 60 s) and 79 “minor” capnograph events (hypercarbaria or hypocarbia) were observed. A number of problems fulfilled criteria in multiple categories. Infants less than or equal to 6 months of age had the highest incidence of major desaturation events (18 of 65 [27%]) compared to toddlers 7-24 months of age or children greater than 24 months of age (P less than 0.001). Blinding the oximeter data increased the number of patients (12 vs. 31) experiencing major desaturation events (P = 0.003); blinding the capnograph data altered neither the frequency of desaturation events nor the incidence of major capnograph events.

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Pulse Oximetry and Capnography in Lung Function Laboratories: a 2004 study.

Objective was to compare values reflecting oxyhemoglobin saturation obtained by pulse oximetry (SpO2) and values for end-tidal carbon dioxide pressure (EtCO2) obtained by capnography with direct measures of gas saturation values and pressures (PaO2 and PaCO2) in arterial blood gas samples. Both measurement devices (pulse oximeter and capnograph) are appropriate for use in a lung function laboratory. The difference between EtCO2 and the PaCO2 should be kept in mind. The findings of the present study indicate that oxyhemoglobin saturation estimated as SpO2 by pulse oximetry adequately reflects arterial blood oxyhemoglobin saturation. EtCO2 obtained by capnography enabled estimation of alveolar ventilation, with a bias in the same direction–since it indirectly reflects PaCO2. However, these two devices for automatic measurement have certain limitations and appropriate applications, which interpreters should be aware of and take into proper consideration.

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Application of capnography and SpO2 measurement in the evaluation of respiratory failure in patients with chronic obstructive pulmonary disease: a 2010 study.

In patients with COPD (especially those with also type II respiratory failure), the modified monitoring method of PCO2 and maintenance of SpO2 above 90% can precisely estimate PaCO2 and PaO2. This method is feasible for clinical noninvasive and dynamic evaluation of respiratory failure in COPD patients, especially in primary care facilities where arterial blood gases analysis is not available.

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Common causes of hypoxemia:

Hypoxemia SpO2 by pulse oximetry EtCO2 by capnography Can supplemental O2 raise SpO2?
Hypoventilation Low High Yes
Low inspired O2 (e.g. high altitude) Low Low due to hypoxemia induced hyperventilation Yes
R to L shunt Low Normal No but with small shunt yes
V/P mismatch Low Normal Yes
Diffusion defect Low Normal Yes

Three points emerge from above table:

1. Only hypoventilation causes hypoxemia with hypercapnia. All other causes of hypoxemia have no hypercapnia.

2. Supplemental oxygen raises SpO2 in almost all cases of hypoxemia.

3. Capnography is useful essentially in hypoventilation but of no use in all other causes of hypoxemia.

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Transcutaneous Carbon dioxide and Oxygen monitoring:

Transcutaneous measurements of oxygen and carbon dioxide are based on the principle that a heating element in the electrode elevates the temperature of the underlying tissues. This increases the capillary blood flow and the partial pressure of oxygen and carbon dioxide, and makes the skin permeable to gas diffusion. It must be remembered that the electrode is measuring the gas tensions of the underlying tissue and not the arterial gas tension. When haemodynamic conditions are stable, the transcutaneous measurements correlate well with arterial values but are not identical. The actual level of transcutaneous oxygen reflects the relationship between the increase in partial pressure in the capillary blood due to heating, the level of skin blood flow and the metabolic oxygen consumption of the skin. In spite of these physiological factors, when blood flow is normal, transcutaneous oxygen values can reliably reflect arterial values. In the case of PtcCO2, the elevated temperature at which the transcutaneous electrode operates in order to increase skin permeability will also raise skin metabolism and lead to an increase in CO2 production. The measured values will, therefore, be significantly higher than arterial values at 37 C. The transcutaneous values can be temperature corrected, thus enabling a readout of values comparable to those at the normal body temperature. These will deviate by a small metabolic contribution from the carbon dioxide production in the epidermis. Transcutaneous monitoring of carbon dioxide tension (PCO2) has been shown to be more reliable than the transcutaneous measurement of oxygen due to the greater diffusion capacity of carbon dioxide through the skin. The more recent development in transcutaneous technology has been the introduction of a solid-state combined PtcO2/PtcCO2 electrode with the glass section of the PtcCO2 electrode being strengthened by incorporation of ceramic material, making it much more robust and less liable to damage.

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Site selection:

The absolute value of PtcO2 is affected by skin thickness and capillary density. It is therefore important to place the electrode at a site of high capillary density and minimal thickness for optimal transcutaneous measurements. This presents no problem in the newborn, in whom these conditions are usually fulfilled. In adults, there is greater variation from site to site and the suggested locations for optimal transcutaneous measurements are the forearm, chest or abdomen.

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Combination of pulse oximetry with transcutaneous CO2 sensor:

The TOSCA monitor (Linde Medical Sensors AG, Basel, Switzerland) combines pulse oximetry (SpO2) and transcutaneous PCO2 (PtcCO2) monitoring in a single ear sensor:

Monitoring carbon dioxide tension and arterial oxygen saturation by a single earlobe sensor in patients with critical illness or sleep apnea: a 2005 study:

The purpose of the study was to evaluate a novel, combined sensor for transcutaneous monitoring of arterial oxygen saturation and carbon dioxide tension. The new monitoring technique was compared to established reference methods. Continuous measurements were performed over several hours by the novel heated (temperature, 42 degrees C) earlobe sensor (TOSCA; Linde Medical Sensors; Basel, Switzerland), incorporating electrochemical and optical elements for carbon dioxide measurement (PtcCO2) and pulse oximetry (SPO2), respectively. The data were compared to the results of repeated arterial blood gas analyses in critically ill patients and to simultaneous nocturnal pulse oximetry performed with different devices with earlobe or finger sensors in sleep apnea patients. In critically ill patients, the mean difference and limits of agreement (bias +/- 2 SDs) of transcutaneous PtcCO2 vs arterial PaCO2 were 3 +/- 7 mm Hg; the corresponding values for changes in PtcCO2 vs PaCO2 were 1 +/- 6 mm Hg. The bias +/- 2 SDs for pulse oximetric SpO2 vs arterial oxygen saturation (SaO2) were 1 +/- 4%. In sleep apnea patients, the combined earlobe sensor identified more transient oxygen desaturations, and the rate of change in oxygen saturation during events was greater compared to those with other tested pulse oximeters, indicating a faster response. Due to its ability to accurately assess both ventilation and oxygenation by a single transcutaneous sensor, the described noninvasive monitoring technique is a valuable tool for respiratory monitoring with potential applications in critical care and sleep medicine.

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Integrated Pulmonary Index:

Integrated Pulmonary Index (IPI) is a patient pulmonary index which uses information from capnography and pulse oximetry to provide a single value that describes the patient’s respiratory status. IPI may be used by clinicians to quickly assess the patient’s respiratory status to determine the need for additional clinical assessment or intervention. The IPI incorporates four patient parameters (end-tidal CO2 and respiratory rate measured by capnography, as well as pulse rate and blood oxygenation SpO2 as measured by pulse oximetry) into a single index value. The IPI value on the patient monitor indicates the patient ventilatory status, where a score of 10 is normal, indicating optimal pulmonary status, and a score of 1 or 2 requires immediate intervention. The IPI algorithm was developed based on data from a group of medical experts (anaesthesiologists, nurses, respiratory therapists, and physiologists) who evaluated cases with varying parameter values and assigned an IPI value to a predefined patient status. A mathematical model was built using patient normal ranges for these parameters and the ratings given to various combinations of the parameters by these professionals. Fuzzy logic, a mathematical method which mimics human logical thinking, was used to develop the IPI model. Clinical validation studies indicate that the IPI value produced by the IPI algorithm accurately reflects the patient’s ventilatory status. In studies on both adult and pediatric patients, in which experts’ ratings of ventilatory status were collected along with IPI data, the IPI scores were found to be highly correlated with the experts’ annotated ratings. IPI can promote early awareness to changes in a patient’s ventilatory status. The caregiver can view the IPI trend, which indicates changes in IPI over time. A quick view of the IPI trend can show that if the IPI has changed over the previous minutes or hours, to help the clinician ascertain if the patient’s overall ventilatory status is worsening, remaining steady, or improving. This information can help determine the next steps in patient care. Thus, IPI can simplify the monitoring of patients in clinical environments. The caregiver can quickly and easily assess a patient’s ventilatory status by following one number, the IPI, before checking the four parameters that make up this number. The four parameters continue to be displayed on the monitor screen. A significant change in the IPI is a “red flag” indicator, indicating that the clinician should review other monitored data and assess the patient. In the clinical environment, a quick check of the IPI value and IPI trend is a first indicator of pulmonary status of the patient and may be used to determine if further patient assessment is warranted. IPI can increase patient safety, by indicating the presence of slow-developing patient respiratory issues not easily identified with individual instantaneous data to the caregiver in real time. This enables timely decisions and interventions to reduce patient risk, improve outcomes and increase patient safety. Since normal values for the physiological parameters are different for different age categories, the IPI algorithm differs for different age groups (three paediatric age groups and adult). IPI is not available for neonatal and infant patients (up to the age of 1 year).

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Innovations in the conventional two wavelength (660 and 940nm) pulse oximeter:

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Since first generation devices, technical advances which have been made to improve pulse oximetry include:

● Calibration resistors and chips embedded into the sensor to compensate for LED differences

● The use of ECG synchronization techniques to anticipate arterial pulses by simultaneously recording the electrocardiograph.

● Various motion sensing improvements to help with reducing artifact and low pulsatile flow situations. An example of a new development can be found at Masimo SET (vide infra)

● Specialty sensors for high altitude climbers, resuscitation situations and cyanotic babies.

● Smart alarm systems for pulse oximeters.

● A reduction in size, cost and power use. Researchers at MIT have developed a ring sized pulse oximeter.

● Fingertip pulse oximeters with wireless connection via Bluetooth technology are made by NONIN

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Wavelength selection for low-saturation pulse oximetry:

Conventional pulse oximeters are accurate at high oxygen saturation under a variety of physiological conditions but show worsening accuracy at lower saturation (below 70%). Numerical modelling suggests that sensors fabricated with 735 and 890 nm emitters should read more accurately at low saturation under a variety of conditions than sensors made with conventionally used 660 and 900 nm band emitters. Recent animal testing confirms this expectation. It is postulated that the most repeatable and stable accuracy of the pulse oximeter occurs when the fractional change in photon path lengths due to perturbations in the tissue (relative to the conditions present during system calibration) is equivalent at the two wavelengths. Additionally, the penetration depth (and/or breadth) of the probing light needs to be well matched at the two wavelengths in order to minimize the effects of tissue heterogeneity. At high saturation these conditions are optimally met with 660 and 900 nm band emitters, while at low saturation 735 and 890 nm provide better performance.

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Advanced pulse oximetry:

Signal extraction technology (SET):

For many years, bioengineers realized that the movement of blood in the venous circulation in a tissue might introduce a significant degree of “noise” to the pulse oximetry readings, which may interfere with these devices displaying readings in situations of low perfusion or movement. Because of this noise, traditional pulse oximeters are subject to false alarms or inaccurate readings, often in critical situations. In 1995, Masimo (Irvine, California) introduced an advanced method of obtaining pulse oximetry readings, using what it calls signal extraction technology (SET).  These devices include the traditional-appearing Pronto pulse oximeter as well as the touchscreen Pronto-7. Many studies have demonstrated the advantages of SET in a variety of clinical situations. For example, it has been shown that Masimo’s SET pulse oximeters in the neonatal intensive care unit can reduce the incidence of retinopathy of prematurity by helping to control oxygen exposure. The technology also reduces the number of false alarms in critical care situations because SET pulse oximeters can obtain accurate readings under circumstances of low perfusion or movement.  Masimo’s SET pulse oximeters and sensors were exclusively used in the 2 studies that were the basis for the Critical Congenital Heart Disease (CCHD) workgroup decision to recommend newborn screening, and the devices were the first to receive US Food and Drug Administration (FDA) clearance with labelling for CCHD screening.

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Twenty-four years ago, two young engineers asked themselves why pulse oximetry wouldn’t work during patient motion and low perfusion–and by doing so, set a new course that created a revolution in patient monitoring. Since its inception, pulse oximetry was plagued by unreliability when it was needed most–during patient motion and low perfusion. The industry had given up and considered the problem “unsolvable.” Clinicians were forced to live with the results–excessive false alarms, delayed notification due to long averaging times, inaccurate data, and an inability to obtain data on the most critical patients. Conventional pulse oximetry works under the assumption that by looking at only the pulse and normalizing the pulsating signal over the non-pulsating signal, oxygen saturation (SpO2) can be measured without calibration. Although this was a big step forward in the evolution of pulse oximetry, it has one major flaw–it assumes the only pulsating component is arterial blood. Unfortunately for conventional pulse oximetry, venous blood moves every time the patient moves or breathes. This causes conventional pulse oximeters to display false low or high SpO2 and pulse rates–resulting in false alarms as high as 90% in ICUs and recovery rooms. When Joe Kiani and Mohamed Diab looked at the same pulse oximetry signal differently than anyone had before, they created new possibilities. By employing advanced signal processing techniques–including parallel engines and adaptive filters–they believed they could find the true arterial signal that would allow accurate monitoring of arterial oxygen saturation and pulse rate, even during the most challenging conditions. Signal Extraction Technology assumes that both the arterial and venous blood can move and uses parallel signal processing engines to separate the arterial signal from sources of noise (including the venous signal) to measure SpO2 and pulse rate accurately, even during motion. Conventional pulse oximetry uses the standard red over infrared algorithm to provide SpO2, while SET uses that conventional algorithm but has added four other algorithms that all run in parallel. These algorithms allow the distinction between arterial and venous signal during motion and low perfusion by identifying and isolating the non-arterial and venous noise SpO2 from the true arterial SpO2 components in the signal. Because of its unmatched reliability during challenging conditions of motion and low perfusion, clinicians at thousands of hospitals around the world count on SET pulse oximeter every day to help them care for patients. And while many leading hospitals have already integrated SET pulse oximetry technology, more are converting every day. These hospitals and clinicians trust SET to help them deliver the most effective and efficient patient care possible. With fewer false alarms, clinicians can focus on the patients who need the most attention. With more trustworthy measurements, clinicians can more tightly control oxygenation levels. And with more timely detection of true events, clinicians can intervene earlier for better patient outcomes and improved patient safety.

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Clinical Accuracy of SET pulse oximetry:

To date, more than 100 independent and objective studies have shown that SET outperforms all other pulse oximetry technologies, providing clinicians with unmatched sensitivity and specificity to make critical patient care decisions. Published papers have compared signal extraction technology to other pulse oximetry technologies and have demonstrated consistent favorable results for signal extraction technology. Signal extraction technology pulse oximetry performance has also been shown to translate into helping clinicians improve patient outcomes. In one study, retinopathy of prematurity (eye damage) was reduced by 58% in very low birth weight neonates at a center using signal extraction technology, while there was no decrease in retinopathy of prematurity at another center with the same clinicians using the same protocol but with non-signal extraction technology.  Other studies have shown that signal extraction technology pulse oximetry results in fewer arterial blood gas measurements, faster oxygen weaning time, lower sensor utilization, and lower length of stay. The measure-through motion and low perfusion capabilities it has also allow it to be used in previously unmonitored areas such as the general floor, where false alarms have plagued conventional pulse oximetry. As evidence of this, a landmark study was published in 2010 showing clinicians using signal extraction technology pulse oximetry on the general floor were able to decrease rapid response team activations, ICU transfers, and ICU days.

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With SET pulse oximetry, false alarms have been reduced by over 95%, while true alarm detection has increased to over 97%–even during conditions of motion and low perfusion.

 

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Detection of SpO2 in patients with extremely low Cardiac Output or Cardiac Standstill:

Sensitivity of Pulse Oximeter system during extremely low local perfusion:

Attempts have been made to maximize sensitivity for detecting pulsation and SpO2 values in patients suffering from extremely low cardiac output and/or low local perfusion levels. Signal extraction technology can read perfusion levels at least 10 fold lower than conventional pulse oximeters. SET pulse oximeter provides valuable information (when other pulse oximeters cannot) in critical situations where very low perfusion can occur, such as ICU, Trauma, Cardio-Pulmonary Bypass and, resuscitation.

The level of SpO2 in a dying or dead patient:

This is somewhat variable and depends on the cause of death and the clinical treatment the patient is receiving at the time of death. However, it is quite possible for a dying or dead patient to have a high SpO2 value. This is the case when peripheral oxygen consumption is quite low, resulting in an increased mixed venous saturation. If extraction is very low and the patient is still receiving oxygen therapy, it is easily possible for the patient to have a high SpO2 value.

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Additionally, the Pronto and Pronto-7 oximeters can be used to estimate the arterial hemoglobin content (called SpHb) when used with proprietary “rainbow” sensors that use 7 separate wavelengths of light to obtain their measurements. Current SpHb sensors are too large to be used with small children, but Masimo just recently developed a sensor for use in children weighing as little as 10 kg. This new sensor is presently being evaluated by the FDA. A consumer version of Masimo’s SET pulse oximeter sensor can be used with an application that runs on iOS or Android.

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Masimo pulse oximeters produce a measurement called the perfusion index (PI) that has been shown to correlate with the well-being of premature babies in the first weeks of life. The PI is the ratio of the pulsatile blood flow to the nonpulsatile or static blood in peripheral tissue and it represents a noninvasive measure of peripheral perfusion.  In 1995 Masimo introduced perfusion index, quantifying the amplitude of the peripheral plethysmograph waveform. Perfusion index has been shown to help clinicians predict illness severity and early adverse respiratory outcomes in neonates, predict low superior vena cava flow in very low birth weight infants, provide an early indicator of sympathectomy after epidural anesthesia, and improve detection of critical congenital heart disease in newborns.

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In 2007, Masimo introduced the first measurement of the pleth variability index (PVI), which multiple clinical studies have shown provides a new method for automatic, noninvasive assessment of a patient’s ability to respond to fluid administration. Appropriate fluid levels are vital to reducing postoperative risks and improving patient outcomes: fluid volumes that are too low (under-hydration) or too high (over-hydration) have been shown to decrease wound healing and increase the risk of infection or cardiac complications. Recently, the National Health Service in the United Kingdom and the French Anesthesia and Critical Care Society listed PVI monitoring as part of their suggested strategies for intra-operative fluid management.

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Non-invasive pulse co-oximeter:

All pulse oximeters in common use measure tissue light transmission at two wavelengths (two colors) to estimate arterial hemoglobin saturation. With only two wavelengths, these pulse oximeters must “assume” the presence of only two light absorbers in the blood: oxyhemoglobin and reduced hemoglobin. If any other light absorbers are present in the blood, the pulse oximeter’s calibration may be invalid. Intravenous injection of dyes such as methylene blue can cause very low oxygen saturation (SpO2) readings—as low as 4% in one study. The common dyshemoglobins, methemoglobin and carboxyhemoglobin, have been shown to produce serious errors in SpO2 readings in animal studies.  These errors have been confirmed in clinical case reports.  No previous commercially produced pulse oximeter has successfully measured these dyshemoglobins, or even provided accurate SpO2 values in their presence. Given the life-threatening dangers of methemoglobin and carboxyhemoglobin toxicity, a pulse oximeter capable of measuring these dyshemoglobins would be an important addition to our monitoring armamentarium. Masimo has now developed such an instrument, the Rainbow-SET Rad-57 Pulse CO-Oximeter (Masimo Inc., Irvine, CA). The Rad-57 uses eight wavelengths of light instead of the usual two and is thereby able to measure more than two species of human hemoglobin. It is approved by the US Food and Drug Administration for the measurement of both carboxyhemoglobin and methemoglobin. In addition to the usual SpO2 value, the Rad-57 displays SpCO and SpMet, which are the pulse oximeter’s estimates of carboxyhemoglobin and methemoglobin percentage levels, respectively.

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Measurement of Carboxyhemoglobin and Methemoglobin by Pulse Co-oximetry: a 2006 study:

A new eight-wavelength pulse oximeter is designed to measure methemoglobin and carboxyhemoglobin, in addition to the usual measurements of hemoglobin oxygen saturation and pulse rate. This study examines this device’s ability to measure dyshemoglobins in human volunteers in whom controlled levels of methemoglobin and carboxyhemoglobin are induced. The Rad-57 measured carboxyhemoglobin with an uncertainty of 2% within the range of 0–15%, and it measured methemoglobin with an uncertainty of 0.5% within the range of 0–12%. Masimo Rainbow-SET Rad-57 Pulse CO-Oximeter can detect and measure both methemoglobin and carboxyhemoglobin within the ranges covered by this experiment: 0–12% for methemoglobin and 0–15% for carboxyhemoglobin.  This study did not investigate the accuracy of the Rad-57 for the measurement of SpO2. The Rad-57 currently uses the same two-wavelength SpO2 calculation algorithm used by previous Masimo SET pulse oximeters, and the accuracy will therefore be the same as those instruments. Because it calculates SpO2 using two wavelengths (as opposed to the eight wavelengths used to calculate SpMet and SpCO), the Rad-57 SPO2 readings will be subject to the usual errors induced by methemoglobin and carboxyhemoglobin, as discussed before.

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With any new technology, questions arise and suspicions abound. Touger et al, in an Annals of Emergency Medicine paper published in October 2010, suggested the RAD-57 was not accurate. In his New York City (Jacobi Medical Center) study of CO poisoned patients, the RAD-57 had a sensitivity of only 48%, meaning that only 48% of actually CO poisoned patients were detected by the device. As expected, the manufacturer vigorously defended their device, suggesting that the Touger study was yet one negative appraisal of their technology amidst a plethora of more favorable evaluations. Many EMS systems, in apparent deference to skepticism, put the brakes in widespread use of RAD-57 technology. Even the Eagles, a cutting edge (and perhaps the premier annual) EMS scientific conference offered an analysis of Touger and its implications for EMS. In July 2011 came Roth et al, also in Annals of Emergency Medicine. In this (massively larger) study done at AKH, one of the biggest hospitals in Vienna, Austria, the RAD-57 had a sensitivity of 94%. The authors concluded that the RAD-57 most certainly could reliably screen large numbers of potentially CO poisoned patients. Roth evaluated 1,578 patients compared to 120 patients in the Touger study.

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Total hemoglobin measurement by non-invasive pulse co-oximetry:

Hemoglobin can be measured on a variety of devices using different principles of operation. Non-invasive pulse Co-oximetry represents the latest development in hemoglobin measuring technology. Pulse Co-oximetry (Masimo Corp, Irvine, CA, USA) is commercially available technology that allows for the continuous non-invasive measurement of haemoglobin, referred to as SpHb. This technology uses a multiple wavelength, spectrophotometric sensor that may be an adhesive single use type for continuous monitoring or a reusable finger clip sensor for spot check assessments. Pulse Co-oximetry allows the non-invasive measurement of carboxyhaemoglobin, methaemoglobin, oxygen content, Pleth Variability Index, along with standard pulse oximetry parameters, oxygen saturation, pulse rate, and perfusion index. SpHb measurement with Pulse Co-oximetry is available in a number of devices designed for the continuous monitoring at the hospital bedside (Radical-7, Rad-87) or for spot check applications with hand held devices (Rad-57, Pronto).

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Rad-87

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Rad-87 Measurements:

•Total Hemoglobin (SpHb)

• Oxygen Content

•Carboxyhemoglobin (SpCO)

•Methemoglobin (SpMet)

•Plus: SET measurements of Oxygen Saturation (SpO2), Pulse Rate (PR), Perfusion Index (PI), and Pleth Variability Index (PVI)

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Most of the studies published thus far on the performance of SpHb measurement with Pulse Co-oximetry assess the accuracy of continuous monitoring in surgical patients. Berkow and colleagues investigated the accuracy of SpHb compared to laboratory Co-oximetry measurement of 130 arterial blood samples from 29 complex spine surgery patients and found an absolute bias and standard deviation of 0.8 ± 0.6 g/dL. Causey et al. studied both surgical and intensive care patients and found a similar bias of 0.29 g/dL. In a study on 44 patients with acute haemorrhage during surgery, Lamhaut et al. compared SpHb and capillary haemoglobin measurement to laboratory determination. The authors obtained a total of 85 measurements, which showed a bias of only −0.02 g/dL (SD 1.39) and a precision of 1.11 g/dL (SD 0.83). However, in comparison to laboratory haemoglobin determination, the percentage of outliers was significantly higher with noninvasive than with capillary measurement. Conversely, when Frasca et al.  examined the performance of SpHb in 62 ICU patients providing 471 samples, the bias was 0.0 ± 1.0 g/dL compared to the reference laboratory haematology analyser. However the bias and standard deviation of capillary measurement by HemoCue was 0.3 ± 1.3 g/dL when compared to the reference haematology analyser, significantly higher than SpHb. In general continuous SpHb monitoring accuracy has been found to be comparable to invasive point of care capillary measurement, with some studies showing it to be slightly higher and some studies showing it to be slightly lower when used in the operating room and intensive care unit. There have also been a few studies published in Emergency Room patients. Sjostrand et al. investigated the accuracy of SpHb using repetitive controls of venous blood samples from 30 patients in a tertiary care emergency room. A total of 242 comparative data pairs were obtained, resulting in a mean deviation of −0.47 g/dL (CI −0.39 to −0.09) for SpHb. After exclusion of 5 patients due to low signal quality, the deviation decreased to −0.24 g/dL (CI −0.39 to −0.09). Although the vast majority of published evaluations of SpHb with Pulse Co-oximetry have been accuracy studies, the true clinical benefit of the technology may be as a trend monitor to detect unexpected changes in haemoglobin, such as with occult bleeding, or to confirm expected changes in haemoglobin as they occur during and after transfusion of red blood cells . The rapid and noninvasive measurement of haemoglobin and the availability of continuous haemoglobin data have the potential to be enormously useful in clinical practice in a variety of situations, such as in trauma, gastrointestinal bleeding, in the perioperative setting, or for guiding blood management during invasive interventions.  Because the technology is not intended to replace laboratory measurements, it is less important to receive a measurement that exactly mirrors a laboratory value, rather than to provide continuous information regarding the changes or stability of haemoglobin. For the spot check applications, the immediacy of data and noninvasive nature of the device make it ideal for prehospital triage decisions such as choosing the right hospital. At the hospital, this technology has the potential to assist emergency department staff in making triage priorities and in assigning staff and infrastructure. The ease of use of these devices allows for the universal screening of all presenting patients for anaemia which could indicate occult bleeding or other disease processes requiring intervention. More data from prospective studies is needed to confirm the reliability of this method to guide therapy during surgery or on-going bleeding. Additionally, prospective randomised trials would be desirable to investigate the potential of SpHb monitoring to reduce blood transfusions during surgery or in the intensive care unit. In conclusion, SpHb by Pulse CO-Oximeter is a promising new medical technology that has the potential to improve the process of care and patient outcomes in many different healthcare settings.

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New Study presented at the 2015 Euroanaesthesia Congress evaluated the impact on Mortality and Morbidity with Masimo SpHb and PVI:

The study evaluated Masimo’s parameters of noninvasive, continuous haemoglobin, SpHb, and fluid responsiveness, PVI, with patients in hospital settings. Dr. Sebastien Ponsonnard and researchers at CHU Limoges, Department of Anaesthesiology & Intensive Care, in Limoges, France, evaluated the impact on mortality and morbidity in patients who underwent general anaesthesia at the hospital after the introduction of Masimo SpHb continuous haemoglobin measurement and response to fluid loading by PVI. Operating rooms and ICUs were equipped with Masimo Radical-7 Pulse CO-Oximeter® monitors. Over a six-month period (Feb. 6-Aug. 7, 2014), patients receiving general anaesthesia were monitored noninvasively. At one month, mortality decreased in 2014 (vs. 84/5123 = 1.64% vs. 121/5478 = 2.2%, P = 0.024). In-hospital mortality was not different between the two years. Death in cardiothoracic surgery was slightly lower (P = 0.07). Researchers concluded: “These results suggest that by using a non-invasive monitor, measuring SpHb and fluid loading responsiveness is possible on a large scale. The observed reduction of mortality agrees with multi-centric randomized studies using more invasive monitoring systems and supports the large use of such a device.”

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New method developed for measuring oxygen saturation in capillary blood:

Like the pulse oximeter—the standard oxygen monitor used in the ICU and surgery— the new device determines oxygen levels by noninvasively reading the blood’s color. But unlike the pulse oximeter, this new monitor can zero in on the amount of oxygen reaching specific tissues. An added benefit is that it works even if the patient has no pulse. Brock-Utne, Benaron, Pieter van der Starre, MD, and 16 others produced a study in animals and humans and showed that the device reliably monitors oxygen levels, even in situations in which pulse oximetry fails. The study appeared in the June 2004 Anesthesiology. Among pulse oximetry’s blind spots is one that occurs during bypass surgery. Because the pulse oximeter relies on the pulsing of a patient’s blood vessels to assess the oxygen level, it’s of little use during such an operation, as this pulse ceases.  Many studies from different institutions have shown that between 5 and 10 percent of cardiac bypass patients experience subtle declines in intellectual ability due to diminished oxygen supply to the brain. This new monitor uses shorter light waves, primarily blue and green, to measure the blood’s color. The use of shorter light waves allows the device to monitor only the smallest blood vessels, called capillaries, where oxygen is delivered to the tissues. In contrast, the pulse oximeter’s longer light waves offer information about arteries, which are the larger vessels that merely move the blood to the capillaries. The vascular surgeons believe the device could alert surgeons to a rare but deadly complication of a surgery to repair an aneurysm in the abdominal section of the aorta. In about 3 percent of those undergoing the procedure the colon becomes starved of oxygen. The problem is, there’s no way to detect the problem until days later, and 57 percent die before leaving the hospital. This device will reveal ischemia of the colon while the patient is still in the operating room, giving surgeons a chance to restore flow before damage occurs. The inventor, former Stanford associate professor David Benaron, MD, suggests that the device also shows promise for uses outside of surgery and critical care. Among these: tumor detection and drug development.

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Researchers develop Wearable, Disposable Device for Pulse Oximetry:

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Pulse oximetry is considered to be a noninvasive, painless, general indicator of oxygen delivery to the peripheral tissues (such as the finger, earlobe, or nose). For decades, pulse oximetry has been ubiquitous in the hospital. Now, because of recent advance, this field is poised for a paradigm shift away from simple monitoring devices to advanced products capable of connecting patients to electronic systems that continuously gather data and notify caregivers when values become critical. A group of bioengineering doctoral students at the University of California Berkeley (UC Berkeley) have invented an inexpensive Band-Aid-style oximeter that uses red and green light to non-invasively monitor pulse rate and oxygen level in blood. While this device could revolutionize pulse oximetry monitoring in healthcare settings, the technology might also be applied to measuring other useful biomarkers as one approach to eliminate invasive specimen collection. Conventional pulse oximeters use light-emitting diodes (LEDs) to send red and infrared light through the fingertip or earlobe to detect oxygen saturation. The student scientists explained that the device uses green (532 nm) and red (626 nm) organic light-emitting diodes (OLEDs) with an organic photodiode (OPD)—a semiconductor device that converts light into current—sensitive at specific OLED wavelengths. The sensor’s active layers are deposited from solution-processed materials via spin-coating and printing techniques. Using a solution-based processing system, the researchers deposited the green and red organic LEDs and the translucent light detectors onto a flexible piece of plastic. By detecting the pattern of fresh arterial blood flow the device can calculate a pulse. The organic oximeter sensor is interfaced with conventional electronics at 1 kHz. To determine accuracy, the device’s acquired pulse rate and oxygenation level were calibrated and compared with a commercially available oximeter. In a study comparing this prototype to conventional oximeters, the device measured pulse rate and oxygenation with errors of 1% and 2%, respectively, noted a December 10, 2014, Nature Communications paper.

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iPhone app work as pulse oximeter:

It is the only app that measures both the heart rate and blood oxygen saturation without an external device. It is integrated with Apple’s HealthKit. NOT FOR CLINICAL USE. Pulse Oximeter uses your iPhone’s camera to detect your pulse and oxygen levels from your fingertip.  Whether you are training, doing simple exercise, or just monitoring stress levels, download the App today and use your camera’s flash to monitor your progress! Place the tip of your index finger on the iPhone’s camera, and in a couple of seconds your pulse and oxygen levels will be shown. Results are also recorded in a graph, just tilt iPhone to view Data Chart.

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Samsung’s Galaxy S5 also has app work as pulse oximeter:

Samsung has updated their S Health app in the Galaxy Apps Store, adding some new features, while removing others for users in some countries. New features include weight management, sleeping time, and oxygen saturation measurement. Oxygen saturation, also known as SpO₂, uses the sensor on the back of your Samsung device. Just place your finger on the sensor and measurement will start automatically.

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Wireless Pulse Oximeter shares data with Mobile Devices:

An innovative wireless fingertip pulse oximeter enables clinicians to track and trend measurements through smart mobile devices. The Bluetooth-enabled device allow clinicians to track and trend up to 12 hours of patient measurements on smart mobile devices, and to share that data via standard comma-separated-value (CSV) files, as well as transfer the data to the Apple Health app. Other pulse oximetry software applications allow you to display your pulse oximeter data in a histogram format and also send your pulse oximeter session data to an email address for storage on your personal computer, phone or tablet.

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Wristwatch-style oximeter lets patients’ measure blood oxygen levels remotely:

A new wristwatch-style oximeter will allow COPD patients – and everyone else – to continue with their normal round of daily activities, without having to “take a break” in order to have their blood oxygen levels measured. This oximeter is a device that measures blood oxygen saturation levels – that patients can wear, with information about their current condition monitored by their Bluetooth-connected smartphones.  If a critical blood oxygen threshold that can endanger a patient’s health is recorded, the app that communicates with the device can inform the caregiver of the situation, and appropriate action can be taken.

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MoveSense app makes cell-phone an oxygen saturation monitor without using pulse oximetry:

The ability to accurately measure oxygen saturation without the use of a pulse oximeter is something that has never been achieved, until now. Researchers developed a smartphone app, MoveSense, which monitors cardiopulmonary patients by analyzing the way they walk, then predicts their oxygen saturation level — without the use of a pulse oximeter. Patients wore pulse oximeters (so readings could be compared to MoveSense data) and carried smartphones running MoveSense software, which continuously recorded saturation and motion. Continuous saturation defined categories corresponding to status levels, including transitions. This, by itself, was a new medical observation. Continuous motion was used to compute eight gait parameters from the sensor data. Their existing gait model was then trained with these data points and used to predict transitions in oxygen saturation. The researchers discovered oxygen saturation readings clustered patients into three pulmonary function categories: one with consistently high saturation, one with consistently low saturation, and a third where saturation varied and patients were clinically unstable. In addition, they discovered that analysis of the saturation, combined with the gait data, could predict saturation category with 100 percent accuracy. The model uses a voting scheme to account for patients walking faster and slower, as their hearts and lungs struggle to keep up with demand. The ability to predict the saturation category of the patient internally from motion of the patient externally is remarkable. This new capability will allow medical professionals to monitor patients’ vital signs, predict their clinical stability, and act quickly should their condition decline. Patients need only carry their personal phones during daily living, as testing has shown that periodic samples are sufficient and that even inexpensive smartphones are powerful enough to record these.

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The moral of the story:

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1. Pulse oximetry provides a simple, non-invasive approximation of oxygen saturation of hemoglobin in arterial blood and used in a wide variety of clinical settings either continuously or intermittently. A single one-off reading often isn’t of much use; trends over a period of time give more information. Always measure oxygen saturation before applying oxygen and repeat the measurement after oxygen has been applied.

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2. Hemoglobin molecule has 4 binding site for oxygen molecule. However, hemoglobin is stable only when bound to 4 molecules of oxygen or when not bound to any oxygen. It is very unstable when bound to 1 to 3 molecules of oxygen. Therefore hemoglobin exists in the RBC in the form of deoxygenated hemoglobin with no oxygen bound, or as oxygenated hemoglobin with 4 molecules of oxygen. When all Hemoglobin molecules are bound with 4 molecules of oxygen, we call oxygen saturation 100 %. When 50 % hemoglobin molecules are bound with 4 molecules of oxygen, we call oxygen saturation 50 %. Oxygen saturation is a measure of how much oxygen the hemoglobin is carrying as a percentage of the maximum it could carry. This oxygen saturation in percentage is measured by pulse oximetry.

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3. Pulse oximetry uses light to work out oxygen saturation. Two wavelengths of light are used; 660 nanometers (red) and 940 nanometres (near infrared). At 660nm, deoxyhemoglobin absorbs about ten times as much light as oxyhemoglobin. At the infrared wavelength (940nm), oxyhemoglobin absorbs more light than that of deoxyhemoglobin. The pulse oximeter directly senses the absorption of red and infrared light, and estimates arterial hemoglobin oxygen saturation from the ratio of the pulsatile to the non-pulsatile absorption of red light divided by the same ratio for infrared light transilluminating a finger, ear, or other tissue. A microprocessor integrates the data, and through an elaborate calibration algorithm based on human volunteer data, the oxygen saturation can be estimated. It is interesting to note that the ratios of the ‘AC/DC’ ratios at 660 nm and 940 nm are very similar in both reflection and transmission modes. This means that using the same pulse oximeter with either reflection or transmission probes will produce reliable results. Pulse oximeters cannot determine the concentrations of oxyhemoglobin or deoxyhemoglobin; they provide an estimate of arterial oxygen saturation of hemoglobin rather than a direct measurement. The pulsatile component represents only up to two per cent of the total light absorption by pulse oximetry. This explains how interferences such as movement or low perfusion may have a considerable impact on its accuracy. The pulse oximeter uses empirical calibration curves developed from studies of healthy volunteers to calculate SpO2. Since it is unethical to induce a degree of oxygen saturation below 70% in volunteers, pulse oximeter readings of approximately 70% represent the lowest limit of accurate output. So at low saturation states, pulse oximetry accuracy deteriorates and tends to overestimate the laboratory co-oximeter measured SaO2.

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4. Functional saturation is the ratio of oxygenated haemoglobin to all haemoglobin capable of carrying oxygen; fractional saturation is the ratio of oxygenated haemoglobin to all haemoglobin including those which do not carry oxygen. SpO2 is estimating functional saturation by pulse oximetry while SaO2 is estimating fractional saturation by using arterial blood sample in ABG analyser with co-oximetry. Fractional saturation (SaO2) is approximately 2% lower than functional saturation (SpO2) in a healthy person. ABG analyser without co-oximeter also calculates oxygen saturation ScO2 which is different from SaO2 measured directly by co-oximeter. Calculated ScO2 misses dyshemoglobins while measured SaO2 takes into account dyshemoglobins. So we have three ways of measuring oxygen saturation of hemoglobin; estimation by pulse oximeter (SpO2), calculation by ABG analyser (ScO2) and direct measurement by laboratory co-oximeter (SaO2).

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5. Pulse oximetry SpO2 has many limitations including inaccuracy below 70% saturation, poor perfusion, movement artifact, improper probe position, body temperature, skin pigmentation, henna, nail varnish, dyshemoglobinemia, ambient light, irregular heartbeats, electromagnetic interference, pulsatile veins, intravenous dyes, uncontrolled diabetes mellitus etc. A calculated ScO2 by ABG analyser may be way off the mark and can be clinically misleading. The most accurate way to measure oxygen saturation is direct measurement of an arterial sample in laboratory co-oximeter (SaO2); the only exception being foetal hemoglobin and jaundice.

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6. It is important to understand the difference between the partial pressure of arterial oxygen PaO2, the oxygen saturation of arterial blood (SaO2), the oxygen content of arterial blood CaO2 and the oxygen delivery. Oxygen content depends on the hemoglobin level, SaO2, and the amount of dissolved oxygen. If the haemoglobin level is halved, the oxygen content of arterial blood will be halved even if PaO2 and SaO2 are normal. Oxygen delivery is determined by oxygen content and cardiac output. Mixed venous oxygen saturation (SvO2) is used to help us to recognize when a patient’s body is extracting more oxygen than normally. An increase in extraction (lower SvO2) is the body’s way to meet tissue oxygen needs when the oxygen delivery is reduced to tissues.

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7. Oxygen enters blood from lungs as dissolved oxygen (PaO2) and then binds with hemoglobin (SaO2). After oxygen has entered and dissolved within the blood, then and only then, oxygen can bind to the hemoglobin in the blood. Oxygen leaves blood to be utilized by tissues as dissolved oxygen first and then dissociates from hemoglobin. So dissolved oxygen is available to tissues first and then oxygen bound to hemoglobin. Pulse oximetry cannot measure dissolved oxygen (1.5%) but measure oxygen bound to hemoglobin (98.5%) as oxygen saturation. Supplemental oxygen therapy increases dissolved oxygen resulting in increased oxygen saturation; and even if oxygen saturation is 100% and cannot rise beyond it, oxygen therapy increases oxygen content and delivery by increasing dissolved oxygen in blood although the amount of dissolved oxygen is much lesser than bound oxygen.

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8. Patients who suffer acute major blood loss and become acutely anaemic should be given 100% oxygen to breathe even if SpO2 is normal. This will increase the amount of dissolved oxygen in the blood and will improve tissue oxygen delivery by a small amount. Of course, blood transfusion may be life-saving. On the other hand, blood transfusion would be far more beneficial than supplemental oxygen in improving a chronically anemic & hypoxemic patient’s low SpO2.

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9. Hypoxemia is an important and potentially avoidable cause of morbidity and mortality. Rapid and accurate detection of hypoxemia is critical to prevent serious complications and save life; however, oxygenation is difficult to assess on the basis of physical examination alone. Hypoxemia occurs much before clinical signs appear and clinical signs of hypoxemia are neither easily recognizable nor sensitive nor specific. Because desaturation is detected earlier by pulse oximetry than by clinical observation, the use of pulse oximetry is recommended for any patient at risk for hypoxemia. A study found that the rate of hypoxemia detection increased nearly 20 fold in the pulse oximetry group compared to group not using it. Supplemental oxygen raises SpO2 in almost all cases of hypoxemia due to poor oxygenation.

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10. Pulse oximetry detects hypoxemic hypoxia due to poor oxygenation by measuring oxygen saturation of hemoglobin but cannot detect anemic, circulatory, ischaemic or histotoxic hypoxia. Pulse oximetry does not provide a measure of actual tissue oxygenation.

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11. Using pulse oximetry as a routine fifth vital sign does result in important changes in the diagnoses and treatments of patients at variety of settings including neonatal & paediatric care, emergency & critical care, pre/intra/post-operative care, out-patients & in-patients care and invasive procedures.

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12. A 2014 Cochrane review concluded that the value of pulse oximetry is questionable in relation to improved outcomes, effectiveness, and efficiency but most anaesthesia experts around the world would disagree. The accumulated data indicated that pulse oximeters could prevent 2000 to 10,000 anaesthesia deaths each year from undetected hypoxemia. There is no study that shows pulse oximetry saves life because a randomized trial of nearly 2 million patients would be needed to include mortality as an outcome.

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13. Although the standard manufacturing claim of accuracy for pulse oximeters is ± 2–3% over the range of 70–100% SpO2, a significant proportion of pulse oximeter sensors may be inaccurate. Once in use, there is little evidence that pulse oximeters are ever re-calibrated or have their accuracy assessed.

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14. Pulse oximeter is reliable if the displayed plethysmographic trace resembles an arterial pressure waveform and the pulse rate displayed equals the actual pulse rate of patient. If the SpO2 level is lower than normal, measure SpO2 in another finger of the patient. You may also cross-check pulse oximeter accuracy by using your own finger rather than the patient finger.

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15. During motion and low perfusion, pulse oximeters using signal extraction technology (SET) have 97 % sensitivity and 95 % specificity for estimating oxygen saturation as compared to conventional pulse oximetry having 57 % sensitivity and 72 % specificity. Remember; patient movement, low perfusion and improper probe placement are common causes of false alarms in conventional pulse oximeters.

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16. Studies suggest that pulse oximeter SpO2 overestimates laboratory Co-oximeter measured SaO2 in patients with critical illnesses.

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17. Although pulse oximetry is not an appropriate method of monitoring patients with bronchial asthma, a post-nebulizer saturation of less than 91 % predicts severe asthma.

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18. Pulse oximetry is a worthwhile screening tool for emergency triage.

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19. Pulse oximetry is recommended as a screening method to detect Critical Congenital Heart Disease (CCHD) in new-borns to prevent morbidity and mortality associated with unrecognized CCHD. The new-born pulse oximetry must be done 24 hours after birth when the baby is neither asleep nor crying nor feeding. The screen has a sensitivity of 60% to 75% with conventional pulse oximetry and 93 % with signal extraction technology for critical congenital heart disease.

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20. To limit oxygen toxicity and prevent hyperoxia in premature neonates, pulse oximetry is used so that supplemental oxygen can be tapered to maintain an oxygen saturation of 90%.

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21. It is normal for your oxygen saturation to drop slightly during exercise, because your muscles are extracting more oxygen to handle the extra activity although your cardio-respiratory system is compensating for increased oxygen demand. However a significant drop of SpO2 during routine exercise suggests cardio-pulmonary illness.

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22. Body temperature can cause as much as a 3% difference in the SpO2 measurements. Body temperature affects SpO2 differentially depending upon systemic or local temperature change. In cold weather, body tries to maintain core body temperature by peripheral vasoconstriction reducing peripheral perfusion and thereby giving spurious low SpO2. On the other hand, local hyperthermia (warm digits) gives low SpO2 and local hypothermia (cold digits) give normal SpO2 due to arterial to venous (A-V) shunting in the digits. A-V shunts may be open in warm hands causing “venous pulsations” which result in a lower SpO2 compared to cold hands with no A-V shunting.

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23. There is significant knowledge deficit about pulse oximetry amongst paramedics, nurses and doctors who are using this technology frequently, resulting in failure to understand limitations of pulse oximetry, thus compromising patient safety.

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24. Although pulse oximetry usage is increasing worldwide, its penetrance is low in low-income countries where it is most useful.

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25. Besides detecting hypoxemia in various cardio-respiratory illnesses and at high altitude; pulse oximeter is also useful in controlling oxygen supplementation, monitoring circulation, determining systolic blood pressure, monitoring vascular volume, monitoring desaturation during exercise; and diagnosing peripheral vascular diseases, collateral circulation, distal circulation, sleep apnoea, aspiration, testicular torsion and pulp vitality in dentistry.

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26. Falsely high SpO2 is more dangerous than falsely low SpO2 because it would give unwarranted complacency and prevent appropriate treatment. Significant hypoxia can be masked in carboxyhemoglobinemia, methmoglobinemia, cyanide poisoning and anemia (total hemoglobin < 10gm/dl) due to high SpO2 reading by conventional pulse oximeter. Additionally, high SpO2 level due to supplemental oxygen can mask hypoventilation and high PaCO2 level.

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27. Supplemental oxygen must be given despite normal SpO2 (95 to 100%) in the following conditions:

A. Acute major blood loss

B. Ischaemic chest pain

C. Methmoglobinemia and carboxyhemoglobinemia including smoke inhalation and tobacco smoker.

D. Sickle cell crisis

E. Near drowning

F. Cyanide poisoning

G. Multi-system trauma

H. Restlessness

I. Respiratory distress

J. On assisted ventilation due to any cause

K. Apnoea

L. Cardiac arrest, although pulse oximetry should not be done while doing CPR

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28. A pulse oximeter should never be used during a cardiac arrest situation because of the extreme limitations of blood flow during cardiopulmonary resuscitation and the pharmacological action of vasoactive agents administered during the resuscitation effort. On the other hand, it is quite possible for a dying or dead patient to have a high SpO2 value. This is the case when peripheral oxygen consumption is quite low, resulting in an increased mixed venous saturation. If extraction is very low and the patient is still receiving oxygen therapy, it is easily possible for the patient to have a high SpO2 value.

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29. Pseudo-hypoxemia means normal SpO2 and low PaO2/SaO2 with ABG and co-oximetry. Pseudo-hypoxemia occurs due to faulty equipment, venous blood sample for ABG/co-oximetry, blood sample from ischaemic limb and excessive oxygen consumption following blood sample collection due to massive leucocytosis (leukemia) or thrombocytosis.

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30. Non-invasive ‘pulse co-oximeter’ not only estimates signal extraction technology SpO2 but also estimates dyshemoglobins, total hemoglobin level (SpHb), oxygen content, pulse rate, Perfusion Index (PI), and Pleth Variability Index (PVI).  The rapid and noninvasive measurement of haemoglobin (SpHb); and the availability of continuous haemoglobin data have the potential to be enormously useful in clinical practice in a variety of situations such as trauma, gastrointestinal bleeding and perioperative setting.

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31. Oxygenation is how well oxygen is moving across the alveolar-capillary membrane and into the blood to be carried to tissue. Oxygenation is synonymous with oxygen saturation of hemoglobin. Ventilation, which can be spontaneous (as in breathing) or artificial (as in mechanical ventilation) is the movement of air in and out lungs. Pulse oximetry estimates oxygenation of arterial hemoglobin which is dependent on both alveolar ventilation and pulmonary perfusion. Capnography estimates carbon dioxide removal which is predominantly dependent on alveolar ventilation. During alveolar hypoventilation, as arterial carbon dioxide tension rises so does alveolar carbon dioxide tension (PCO2) because CO2 diffuses rapidly across alveolar capillary membrane; concurrently alveolar PO2 falls, leading to fall in arterial oxygen saturation. If the patient is breathing room air then the saturation will fall early and is a reasonably sensitive indicator of hypoventilation. The situation is different if the patient is receiving supplemental oxygen. The alveolar PO2 will now be much higher and consequently higher PaO2 will raise SpO2.The failure to detect hypoventilation in such a patient is not a failure of pulse oximetry as such but an example of a false sense of security generated by a single physiological variable being within safe limits. It must be understood that a normal reading of SpO2 in the presence of supplemental oxygen gives no information about CO2 removal i.e. the adequacy of ventilation. Oxygenation can be erroneously interpreted as ventilation if EtCO2 by capnography is not monitored.  A recent study found that only 35% of nurses and 39% of physicians in a major medical center knew that pulse oximetry monitored oxygen saturation only and did not reflect changes in ventilation.  All patients who are prone to hypoventilation and/or respiratory depression due to any cause must undergo capnography (EtCO2) along with pulse oximetry (SpO2) to determine both carbon dioxide removal (ventilation) and oxygen saturation (oxygenation).

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32. Hypoventilation can be detected early with pulse oximetry by lower SpO2 if patient is breathing in ambient air. By contrast, poor oxygenation cannot be detected early with capnography by higher EtCO2. Only hypoventilation causes hypoxemia with hypercapnia. All other causes of hypoxemia have no hypercapnia.  Capnography is useful essentially in hypoventilation but of no use in all other causes of hypoxemia. Additionally, the cost and maintenance of oximetry are generally lower than capnography. For these reasons, pulse oximetry is the preferred monitoring modality in resource-limited settings.

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33. Integrated Pulmonary Index (IPI) is a patient pulmonary index which uses information from capnography and pulse oximetry to provide a single value that describes the patient’s respiratory status.  The IPI incorporates four patient parameters (end-tidal CO2 and respiratory rate measured by capnography, as well as pulse rate and blood oxygenation SpO2 as measured by pulse oximetry) into a single index value. IPI score correlate very well with ventilator status of a patient. IPI can increase patient safety, by indicating the presence of slow-developing patient respiratory issues not easily identified with individual instantaneous data available to the caregiver in real time. This enables timely decisions and interventions to reduce patient risk, improve outcomes and increase patient safety.

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34. A critical patient needs repeated arterial punctures for ABG monitoring; today it can be replaced by continuous non-invasive capnography, continuous non-invasive pulse oximetry (preferably pulse co-oximetry) and simple venous blood collection for bicarbonate, electrolytes, hemoglobin and pH. Studies have shown that bicarbonate and pH differ very little between arterial and venous blood.

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Dr. Rajiv Desai. MD.

August 24, 2015

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Postscript:

This article is written not for lay people to do pulse oximetry at home but for medical students, paramedics, nurses and doctors as there is a significant knowledge deficit about pulse oximetry amongst them.

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YOGA

July 20th, 2015

YOGA:

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Marilyn Monroe performs dhanurasana (bow pose) in 1948:

Indra Devi opened yoga studio in Hollywood in 1948 and discovered ready students among movie stars, who found yoga’s breathing and relaxation techniques useful to their work. Her students included Greta Garbo, Gloria Swanson and Marilyn Monroe.

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Prologue:

A considerable number of studies have identified prayer as a frequent and favoured coping method among patients providing each patient with comfort and strength. A variety of studies have attempted to test the efficacy of prayer and found no medical benefit. Prayers offered by strangers had no effect on the recovery of people who were undergoing heart surgery, a large and well-constructed study proved in 2006. The Cochrane Collaboration published a thorough review reaching the same conclusion in 2011 and counselled, “We are not convinced that further trials of this intervention should be undertaken and would prefer to see any resources available for such a trial used to investigate other questions in health care.” God’s medical career was over. But he left a void in the public discussion of medicine, and yoga has filled it. Studies come out on a near weekly basis trumpeting the benefits of yoga for any problem. Yoga for diabetes. Yoga for high blood pressure. Yoga for heart disease. Yoga for cancer. Yoga is a mind and body practice with historical origins in ancient Indian philosophy. Various styles of yoga combine physical postures, breathing techniques, meditation and relaxation. In thousands of years of yoga history, the term “yoga” has gone through a renaissance in current culture, exchanging the loincloth for a leotard and pair of leggings. Carl G. Jung the eminent Swiss psychologist, described yoga as ‘one of the greatest things the human mind has ever created.’ Yoga is considered science of the mind and fitness was not the chief aim of practice although yoga has become popular as a form of physical exercise based upon asanas (physical poses) to promote bodily or mental control and well-being. Sanskrit, the Indo-European language of the Vedas, India’s ancient religious texts, gave birth to both the literature and the technique of yoga.  The Sanskrit word “yoga” has several translations and can be interpreted in many ways. Many translations point toward translations of “to yoke,” “join,” or “concentrate” – essentially as a means to unite body, mind and spirit. Yoga does not contradict or interfere with any religion, and may be practiced by everyone, whether they regard themselves as agnostics or members of a particular faith. Is yoga hype or science?  I attempt to answer this question.

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Note:

The article is published with sole intention to study scientific basis of yoga.  How to do yoga asana, pranayama and meditation with details of different asanas and different pranayamas, and details of specific asana/ pranayama for specific benefit is beyond scope of this article. Nobody should start doing yoga and nobody should stop doing yoga after reading this article. If you want to learn yoga, please contact competent & experienced yoga teacher. Please do read my article on complementary and alternative medicine (CAM) published on this website in august 2010 as medical fraternity consider yoga as part of CAM.

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Yoga terminology:

Yoga (Sanskrit: योग) is a Sanskrit word with a general meaning of “connection, conjunction, attachment, union”: a generic term for several physical, mental, and spiritual disciplines originating in ancient India. Hatha Yoga is the term Yoga is now colloquially (and more commonly) used to refer to as a school which emphasizes physical exercise within the tradition of Raja Yoga. Raja Yoga is a system of meditation in classical Vedanta philosophy. The word yoga, from the Sanskrit word yuj means to yoke or bind and is often interpreted as “union” or a method of discipline. A male who practices yoga is called a yogi, a female practitioner, a yogini.

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A glossary of frequently used Yoga terms:

Asana: Asana is defined as “posture;” its literal meaning is “seat.” Originally, the asanas served as stable postures for prolonged meditation. More than just stretching, asanas open the energy channels (nadiis), and psychic centers (chakras) of the body. Asanas purify and strengthen the body and control and focus the mind. Asana is one of the eight limbs of classical Yoga, which states that asana should be steady and comfortable, firm yet relaxed. There are hundreds of different yoga postures, and they vary among the different styles and disciplines of Hatha Yoga. Teachers will often give the names of the postures in English, Sanskrit or a mix of the two.

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Ashtanga: eight limbs of yoga practice. Each limb relates to an aspect of achieving a healthy and fulfilling life, and each builds upon the one before it.

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Ayurveda: the ancient Indian science of health

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Bhakti: devotion (as in Bhakti Yoga, the yoga of devotion)

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Chakra: Wheel of light – refers to each of the seven physical areas of the body wherein the three main nadis (Sushunma, Ida & Pingala) intersect. The basic system has seven chakras (root, sacrum, solar plexus, heart, throat, third eye and crown), each of which is associated with a color, element, syllable, significance, etc.

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Drishti: gazing point used during asana practice

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Mantra: a repeated sound, syllable, word or phrase; often used in chanting and meditation.

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Meditation: Focusing and calming the mind often through breath work to reach deeper levels of consciousness.

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Mudra: a hand gesture; the most common mudras are anjali mudra (pressing palms together at the heart) and gyana mudra (with the index finger and thumb touching)

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Nadi: Channel for the movement of prana running through the body like a super highway. There are said to be 72,000 channels running through each body.

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Namaste: “I bow to you”; a word used at the beginning and/or end of class which is most commonly translated as “the light within me bows to the light within you”; a common greeting in Indian cultures; a salutation said with the hands in anjali mudra.

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Niyama: five living principles that (along with the yamas) make up the ethical and moral foundation of yoga; they include Sauca (purity), Santosha (contentment), Tapas (burning enthusiasm), Svadhyaya (self-study) and Ishvarapranidhana (celebration of the spiritual)

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Om: the original syllable; chanted “A-U-M” at the beginning and/or end of many yoga classes

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Prana: life energy; chi; qi

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Pranayama: Breathing techniques to build prana, or energy, are known as pranayama. This is an important aspect of the yoga tradition and a part of the physical practice. When holding a yoga posture, make sure you can breathe slowly and deeply, using your breath control. A commonly used pranayama in Western classes is known as ujaii breathing, which mimics the sound of the ocean by constricting the throat. This technique links the breath with movements.

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Samadhi: the state of complete Self-actualization; enlightenment

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Savasana: corpse pose; final relaxation; typically performed at the end of every hatha yoga class, no matter what style

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Surya Namaskar: Sun Salutations; a system of yoga exercises performed in a flow or series

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Sutras: classical texts; the most famous in yoga is, of course, Patanjali’s Yoga Sutras.

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Ujjayi (a.k.a as Hissing Breath, Victorious Breath): A type of pranayama in which the lungs are fully expanded and the chest is puffed out; most often used in association with yoga poses, especially in the vinyasa style.

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Vinyasa: Yoga posture sequences are a series of postures arranged to flow together one after the next. This is often called vinyasa or a yoga flow.

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World yoga day:

June 21 was declared as the International Day of Yoga by the United Nations General Assembly on December 11, 2014. The declaration of this day came after the call for the adoption of 21 June as International Day of Yoga by Indian PM Narendra Modi during his address to UN General Assembly on September 27, 2014. In December 2011, international humanitarian, meditation and yoga Guru Sri Sri Ravi Shankar and other yoga gurus supported the cause from the delegation of the Yoga Portuguese Confederation and together gave a call to the UN to declare June 21 as World Yoga Day. Following the adoption of the UN Resolution, Sri Sri Ravi Shankar lauded the efforts of PM Narendra Modi, stating that “It is very difficult for any philosophy, religion or culture to survive without state patronage. Yoga has existed so far almost like an orphan. Now, official recognition by the UN would further spread the benefit of yoga to the entire world.”  “What is performed on the first International Yoga Day are the most popular, easy-to-do loosening exercises,” Isha, a Yoga instructor who learnt the art at Morarji Desai National Institute of Yoga (MDNIY) says, adding that there were over 8.4 million of these exercises.  “Only the basic exercises are done on the International Yoga Day. These would certainly help people understand the importance of yoga in life.”

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The figure below shows use of yoga over time:

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Global yoga statistics:

There are 250 million estimated practitioners of yoga globally.

Around 20.4 million Americans practise yoga.

In the past few years, the number of people practicing yoga has grown about 30%. Interestingly, the amount of money that people are spending on this activity has grown by about 100%!

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Yoga in America:

The 2007 National Health Interview Survey (NHIS) found yoga to be a growing complementary healthcare practice being utilized by approximately 6.1% of U.S. adults. Deep breathing exercises, known in yoga as “pranayama,” and meditation, another aspect often incorporated into yoga practice, were also popular complementary health practices among adults with 12.7% and 9.4%, respectively, of the population practicing (Barnes et al., 2008). The 2007 survey also found that more than 1.5 million children practiced yoga in the previous year. Many people who practice yoga do so to maintain their health and well-being, improve physical fitness, relieve stress, and enhance quality of life. In addition, they may be addressing specific health conditions, such as back pain, neck pain, arthritis, and anxiety. Across America, students, stressed-out young professionals, CEOs and retirees are among those who have embraced yoga, fuelling a $27 billion industry with more than 20 million practitioners — 83 percent of them women. More than 30 percent of Yoga Journal’s readership has a household income of over $100,000.

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Top five reasons people report for taking up yoga are:

1. To increase flexibility;

2. General conditioning of their body and muscles;

3. To find stress relief;

4. To improve their overall health, and;

5. To become more physical fit.

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Yoga in Australia: Results of a national survey in 2012:

Motivations for beginning and continuing yoga practice:

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Table above shows the reasons given for beginning and continuing yoga practice. Respondents were able to select multiple reasons. ‘Health and fitness’, and ‘increased flexibility/muscle tone’ were the most common reasons for starting (both about 71%) and continuing yoga practice (82% and 86% respectively). While 58.4% of respondents gave ‘reduce stress or anxiety’ as a reason for starting, 79.4% found this to be a reason for continuing. Only 19% of students initially saw yoga as a spiritual practice; however, this increased to 43% once practicing. Similarly, 29% initially saw yoga as a form of personal development, increasing to 59% as a reason for continuing to practice. About 20% indicated a specific health or medical reason for practice.

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Why Yoga has become so popular in America? Why India is still not there?

Do you know that there are 20 million yoga practitioners in North America? Yoga has already become a gigantic industry in America if you include yoga studios, yoga retreats, and products like mats, clothing, shoes, and games like Wii fits, conferences, books and videos! Besides, media’s fascination with the fact that celebrities like Madonna and Sting are yoga practitioners glamorizes the image of yoga and leads to more Americans joining this bandwagon. So what is it about it about this 5000-year-old practice, originated in India, to resonate with Americans? All of us know that it can’t be that Americans are running out of options in the market of “keeping fit” as there are just plethora of exercise equipment, gyms, books, videos and exercise programs out there. It is no secret that Americans always had fascination for anything mystique, eastern or oriental with a spiritual flavor. On top of that they have an insatiable need to try anything which can keep them fit. The martial art studios, teaching arts like kung-fu, taekwondo, karate and judo did address both aspects to some extent, but remained confined to teenagers or people who were relatively younger. Somehow, most people could not integrate martial arts as a part of their life style as strenuous routines were hard for people as they got older. Whereas, Yoga’s adoption by all age groups grew in leaps and bounds and you couldn’t surpass a busy street without seeing anyone carrying a yoga mat. There are various flavors of yoga which is common in America like Vinyasa, Iyenger, Kundalini, Kriya, Bikram, power, mild, hath and many others – each is designed to meet you where you are and based on your needs. Yoga practitioners in America actually believe that they can find a yoga pose for every ailment in your body! Finally, Yoga is turning out to be much more than various “stretching” routines and is making them understand difference between “health” and “fitness”. Perhaps the best way to understand yoga’s popularity in America is to go right to the people who practice it. If you ask them why the practice, some of the more common replies you might hear are flexibility, increased energy, improved focus, reduction of the symptoms associated with stress and an overall good feeling. It is claimed that yoga can have a rejuvenating effect on all systems of the body including the circulatory, glandular system, digestive, nervous, musculoskeletal, and reproductive and respiratory systems. Let’s talk about Indian now! What is the state of Yoga in India? According to Sri Sri Ravi Shankar, a world-renowned spiritual leader, “If an individual can be credited with reviving yoga in India, it is solely Swami Ramdev. Unperturbed by issues and controversies generated, he has done a phenomenal job in re-introducing Yoga at a national level”. But Indians still have a long way to go as far as adaption of yoga at grassroots level is concerned. The percentage of population practicing it daily is very low if you compare it with America. Yoga is free and practice of yoga doesn’t require any investment other than time. Indians should be leading rest of the world again as far as yoga is concerned because it has always been a part of India’s tradition.

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Commercialization of Yoga:

Most of what is billed as yoga around the world is not the yoga described in the Yoga Sutras or any of the original texts. Rather it has morphed into a form of asana without faith, devotion, or understanding underlying it, and therefore, more akin to mere exercise. New types of “yoga” seem to appear and disappear, it seems almost daily, and they are a far cry from the yoga described in the Yoga Sutras, Bhagavad Gita, or Upanishads. In today’s mass commercialization, the term “yoga” is loosely applied to the latest fitness creation that bears little to no resemblance to yoga as citta-vritti-nirodhah. The result of this has been a decline of yoga as an inward, spiritual quest or journey into a multi-million dollar commercialized industry. This commercialization is problematic in general, but it is of particular to concern to Hindus who see yoga being delinked from its roots. And though yoga is a means of spiritual attainment for any and all seekers, irrespective of faith or no faith, its underlying principles are those of Hindu thought. Yoga has gotten so big and has had such great commercial success that there is now a business category known as the “Yoga Industry”. Googling the term “Yoga Industry” reveals about 59,300,000 results.

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Introduction to yoga:

All of us know that Yoga originated in India and the history of yoga can be traced back to Indus Valley civilization. Maharshi Patanjali is regarded as the founder of yoga and “Yoga Sutras” written by him are considered by many as the foundational text of Yoga. The Sanskrit word yoga has many meanings and is derived from the Sanskrit root “yuj,” meaning “to control,” “to yoke” or “to unite. The word is basically associated with spiritual and meditative practices in Hinduism, Jainism and Buddhism. Ironically, yoga was developed by men and practiced nearly exclusively by men for centuries.  It is only in recent western history that so many women have flocked to the practice. Still, many present day popular teachers and gurus are men.

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Yoga etymology:

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In philosophical terms, yoga refers to the union of the individual self with the universal self. Yoga is one of six branches of classical Indian philosophy and has been practiced for thousands of years. References to yoga are made throughout the Vedas, ancient Indian scriptures that are among the oldest texts in existence. Two thousand years ago the Indian sage Patanjali codified the various philosophies and methodologies of yoga into 196 aphorisms called “The Yoga Sutras,” which helped to define the modern practice of yoga. The Sutras outline eight limbs, or disciplines, of yoga: yamas (ethical disciplines), niyamas (individual observances), asana (postures), pranayama (breath control), pratyahara (withdrawal of senses), dharana (concentration), dhyana (meditation), and samadhi (self-realization, enlightenment). For common people, the term yoga usually refers to the third and fourth limbs, asana and pranayama, although traditionally the limbs are viewed as interrelated. Currently many styles of yoga are practiced (e.g., Iyengar, Ashtanga, Vini, Kundalini, Bikram), some of which are more closely tied to a traditional lineage than others. It is important to note that each of these approaches represents a distinct intervention, in the same way that psychodynamic, cognitive-behavioral, and interpersonal therapies each involve different approaches to psychotherapy. These styles of yoga emphasize different components and also have diverse approaches to and standards for teacher training and certification.

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Yoga, in ancient times, was often referred to in terms of a tree with roots, trunk, branches, blossoms and fruits. Each branch of yoga has unique characteristics and represents a specific approach to life.

The six branches are:

1. Hatha yoga – physical and mental branch – involves asana and pranayama practice – preparing the body and mind

2. Raja yoga – meditation and strict adherence to the “eight limbs of yoga”

3. Karma yoga – path of service to consciously create a future free from negativity and selfishness caused by our actions

4. Bhakti yoga – path of devotion – a positive way to channel emotions and cultivate acceptance and tolerance

5. Jnana yoga – wisdom, the path of the scholar and intellect through study

6. Tantra yoga – pathway of ritual, ceremony or consummation of a relationship.

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In other parts of the world where yoga is popular, notably the United States, yoga has become associated with the asanas (postures) of Hatha Yoga, which are popular as fitness exercises. Yoga as a means to enlightenment is central to Hinduism, Buddhism, Sikhism, and Jainism, and has influenced other religious and spiritual practices throughout the world. The ultimate goal of yoga is the attainment of liberation (Moksha) from worldly suffering and the cycle of birth and death. Yoga entails mastery over the body, mind, and emotional self, and transcendence of desire. It is said to lead gradually to knowledge of the true nature of reality. The Yogi reaches an enlightened state where there is a cessation of thought and an experience of blissful union. This union may be of the individual soul (Atman) with the supreme Reality (Brahman), as in Vedanta philosophy; or with a specific god or goddess, as in theistic forms of Hinduism and some forms of Buddhism.

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What does Om mean?

Om is a mantra, or vibration, that is traditionally chanted at the beginning and end of yoga sessions. It is said to be the sound of the universe. Chanting Om allows us to recognize our experience as a reflection of how the whole universe moves—the setting sun, the rising moon, the ebb and flow of the tides, the beating of our hearts. As we chant Om, it takes us for a ride on this universal movement, through our breath, our awareness, and our physical energy and we begin to sense a bigger connection that is both uplifting and soothing.

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Yoga is a Hindu spiritual and ascetic discipline, a part of which, including breath control, simple meditation, and the adoption of specific bodily postures, is widely practised for health and relaxation. Yoga is an exercise practice that combines breathing exercises, physical postures, and meditation. The whole system of Yoga is built on three main structures: exercise, breathing, and meditation. The exercises of Yoga are designed to put pressure on the glandular systems of the body, thereby increasing its efficiency and total health. The body is looked upon as the primary instrument that enables us to work and evolve in the world, and so a Yoga student treats it with great care and respect. Breathing techniques are based on the concept that breath is the source of life in the body. The Yoga student gently increases breath control to improve the health and function of both body and mind. These two systems of exercise and breathing then prepare the body and mind for meditation, and the student finds an easy approach to a quiet mind that allows silence and healing from everyday stress. Regular daily practice of all three parts of this structure of Yoga produce a clear, bright mind and a strong, capable body.

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Yoga is a full-body workout that increases flexibility, endurance, strength, balance and mental clarity through the use of postures, breathing techniques and concentration. It combines muscle strengthening and toning with flexibility and stretching exercises as well as breathing and meditation to attain maximum results. It is an exercise and meditation regimen that some people even consider to be a lifestyle. Yoga helps correct posture by increasing core strength and by encouraging correct alignment. To increase strength and endurance, participants practice holding static poses for longer periods of time. The mind and body exercise regimen requires the practitioner to focus on breathing. This helps reduce stress and anxiety and encourages relaxation and a sense of calm.

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This is how I view yoga, a discipline involving controlled breathing, prescribed body positions, and meditation, with the goal of attaining a state of deep spiritual insight and tranquillity. First you have to adopt a specific posture to stretch muscles, improve flexibility and do isometric exercise. While doing posture, you concentrate on breathing. Controlled breathing helps to gain conscious control over bodily functions. Breath control and breathing exercise would lead to meditation and relaxation. Yoga is a synchronisation of posture, breathing and meditation.

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Anyone can practise yoga. You don’t need special equipment or clothes – just a small amount of space and a strong desire for a healthier, more fulfilled life. The yoga postures or asanas exercise every part of the body, stretching and toning the muscles and joints, the spine and the entire skeletal system. And they work not only on the body’s frame but on the internal organs, glands and nerves as well, keeping all systems in radiant health. By releasing physical and mental tension, they also liberate vast resources of energy. The yogic breathing exercises known as pranayama revitalize the body and help to control the mind, leaving you feeling calm and refreshed, while the practice of positive thinking and meditation gives increased clarity, mental power and concentration. Yoga is a complete science of life that originated in India.

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Yoga is traditionally believed to have beneficial effects on physical and emotional health. Over the last several decades, investigators have begun to subject these beliefs to empirical scrutiny. Most of the published studies on yoga were conducted in India, although a growing number of trials have been conducted in the United States and other Western countries. The effects of yoga have been explored in a number of patient populations, including individuals with asthma, cardiac conditions, arthritis, kyphosis, multiple sclerosis, epilepsy, headache, depression, diabetes, pain disorders, gastrointestinal disorders, and addictions (among others),as well as in healthy individuals. In recent years, investigators have begun to examine the effects of yoga among cancer patients and survivors. The term cancer survivor here refers to individuals who have completed cancer treatment. The application of yoga as a therapeutic intervention, which began early in the twentieth century, takes advantage of the various psychophysiological benefits of the component practices. The physical exercises (asanas) may increase patient’s physical flexibility, coordination, and strength, while the breathing practices and meditation may calm and focus the mind to develop greater awareness and diminish anxiety, and thus result in higher quality of life. Other beneficial effects might involve a reduction of distress, blood pressure, and improvements in resilience, mood, and metabolic regulation.

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According to the U.S. Department on Aging, there are four components to good physical health: strength, flexibility, balance and aerobic capacity. It is interesting to note that yoga can help you accomplish all these things, and no fancy piece of equipment is needed other than your own body and a yoga mat.  Over the last 100 years, our lives have become very fast paced: cell phones, computers, internet, television. This, along with a strong work ethic, often results in people out of balance – people experiencing a lot of stress. Consequently, there is a strong need to de-stress, to quiet our minds and rejuvenate our bodies. And yoga helps achieve this, helping us return to a state of balance and health.

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Definition of yoga:

There is no single definition of yoga. In order to experience truth through yoga, we must study its classical definitions and reflect on our own understanding of it.  Yoga practices include posture (asana), breathing (pranayama), control of subtle forces (mudra and bandha), cleansing the body-mind (shat karma), visualizations, chanting of mantras, and many forms of meditation.

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The Indian sage Patanjali is believed to have collated the practice of yoga into the Yoga Sutra an estimated 2,000 years ago. Patañjali’s work was composed in 400 CE plus or minus 25 years. The Sutra is a collection of 196 statements that serves as a philosophical guidebook for most of the yoga that is practiced today. Patanjali’s Yoga Sutras are widely regarded as the first compilation of the formal yoga philosophy. The verses of Yoga Sutras are terse. Many later Indian scholars studied them and published their commentaries, such as the Vyasa Bhashya (c. 350–450 CE). Patanjali’s yoga is also referred to as Raja yoga.

Patanjali defines the word “yoga” in his second sutra:

योग: चित्त-वृत्ति निरोध: (yogaḥ citta-vṛtti-nirodhaḥ) – Yoga Sutras 1.2

The great sage Patanjali, in the system of Raja Yoga, gave one of the best definitions of yoga. He said, ‘Yoga is the blocking (nirodha) of mental modifications (chitta vritti) so that the seer (drashta) re-identifies with the (higher) Self. Patanjali describes Yoga as ‘Chitta Viriddhi Nirodha’ or the opening up of the closed mind. The aim of Yoga is to reach one’s true self and to reach the goal, one has to let go of biases and prejudices. Patanjali’s system has come to be the epitome of Classical Yoga Philosophy and is one of the major philosophies of India. This terse definition hinges on the meaning of three Sanskrit terms. I. K. Taimni translates it as “Yoga is the inhibition (nirodhaḥ) of the modifications (vṛitti) of the mind (citta)”.  Swami Vivekananda translates the sutra as “Yoga is restraining the mind-stuff (Citta) from taking various forms (Vrittis).”  Edwin Bryant explains that, to Patanjali, “Yoga essentially consists of meditative practices culminating in attaining a state of consciousness free from all modes of active or discursive thought, and of eventually attaining a state where consciousness is unaware of any object external to itself, that is, is only aware of its own nature as consciousness unmixed with any other object.”

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According to Sage Patanjali, there are eight aspects of yoga, referred to as ashtanga yoga (Eight-Limbed Yoga), which includes yama (social discipline), niyama (personal discipline), asana (moulding the body into various positions), pranayama (regulation of the breath), pratyahara (involution of the senses), dharana (concentration), dhyana (meditation) and Samadhi (state of bliss). The Yoga Sutras of Patanjali discuss yoga practice in eight stages or limbs of yoga, which together provide a wholistic practice and the guiding principles to bring real happiness and lasting changes in our lives. Only one limb pertains to ‘asana’ (or postures). Classical yoga texts tell us that the last three of Patanjali’s limbs—dharana (deep concentration), dhyana (awareness of existence) and samadhi (oneness or enlightenment)—are to be practiced once we have a foundational understanding of yoga’s powers of illumination. According to B.K.S. Iyengar’s Light on Yoga, we are ready to practice dharana once “the body has been tempered by asanas, when the mind has been refined by the fire of pranayama, and when the senses have been brought under control by pratyahara.”

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Please do not confuse Patanjali’s ashtanga yoga with power yoga which is also called ashtanga yoga.

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According to Jacobsen, Yoga has five principal meanings:

1. Yoga as a disciplined method for attaining a goal;

2. Yoga as techniques of controlling the body and the mind;

3. Yoga as a name of one of the schools or systems of philosophy (darśana);

4. Yoga in connection with other words, such as “hatha-, mantra-, and laya-,” referring to traditions specialising in particular techniques of yoga;

5. Yoga as the goal of Yoga practice.

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Hatha Yoga:

The earliest references to hatha yoga are in Buddhist works dating from the eighth century. The earliest definition of hatha yoga is found in the 11th century Buddhist text Vimalaprabha, which defines it in relation to the center channel, bindu etc. The basic tenets of Hatha yoga were formulated by Shaiva ascetics Matsyendranath and Gorakshanath c. 900 CE. Hatha yoga synthesizes elements of Patanjali’s Yoga Sutras with posture and breathing exercises. Hatha yoga, sometimes referred to as the “psychophysical yoga”, was further elaborated by Yogi Swatmarama, compiler of the Hatha Yoga Pradipika in 15th century CE. This yoga differs substantially from the Raja yoga of Patanjali in that it focuses on shatkarma, the purification of the physical body as leading to the purification of the mind (ha), and prana, or vital energy (tha). Compared to the seated asana, or sitting meditation posture, of Patanjali’s Raja yoga, it marks the development of asanas (plural) into the full body ‘postures’ now in popular usage and, along with its many modern variations, is the style that many people associate with the word yoga today. It is similar to a diving board – preparing the body for purification, so that it may be ready to receive higher techniques of meditation. The word “Hatha” comes from “Ha” which means Sun, and “Tha” which means Moon. This refers to the balance of masculine aspects—active, hot, sun—and feminine aspects—receptive, cool, moon—within all of us. Hatha yoga is a path toward creating balance and uniting opposites. In our physical bodies we develop a balance of strength and flexibility. We also learn to balance our effort and surrender in each pose. The word hatha also means willful or forceful. Hatha yoga includes postures (asana), breathing techniques (pranayama), purification techniques (shat karmas), and energy regulation techniques (mudra and bandha). The definition of yoga in the Hatha Yoga texts is the union of the upward force (prana) and the downward force (apana) at the navel center (manipura chakra). Hatha yoga teaches us to master the totality of our life force, which is also called prana. By learning how to feel and manipulate the life force, we access the source of our being. Hatha yoga is a powerful tool for self-transformation. It asks us to bring our attention to our breath, which helps us to still the fluctuations of the mind and be more present in the unfolding of each moment.

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In the 1980s, yoga was connected to health, legitimizing yoga as a purely physical system of health exercises outside of counter-culture or esotericism circles, and unconnected to any religious denomination. Numerous asanas seemed modern in origin, and strongly overlapped with 19th and early-20th century Western exercise traditions. The West in the early 21st century typically associates the term “yoga” with Hatha yoga and its asanas (postures) or as a form of exercise. Since 2001, the popularity of yoga in the USA has risen constantly. The number of people who practiced some form of yoga has grown from 4 million (in 2001) to 20 million (in 2011). The American College of Sports Medicine supports the integration of yoga into the exercise regimens of healthy individuals as long as properly-trained professionals deliver instruction. The College cites yoga’s promotion of “profound mental, physical and spiritual awareness” and its benefits as a form of stretching, and as an enhancer of breath control and of core strength. Today most people practicing yoga are engaged in the third limb, asana, which is a program of physical postures designed to purify the body and provide the physical strength and stamina required for long periods of meditation.

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Modern Yoga versus Traditional Yoga:

The typical public perception of Yoga has shifted significantly in recent years. The starting point of most classes, books, magazines, articles, websites, and blogs on Yoga are so different from traditional Yoga of the ancient sages that it can be fairly called “Not Yoga”. The wave of Not Yoga seems to morph further and further away from Yoga. Yoga is now so totally altered that we can cry, get angry, or laugh, and laughing might be the most positive. Much, if not most of today’s Yoga can be called “gymnastic yoga” as it has emerged from the gymnastic practices of the late 1800s and early 1900s, not from the ancient traditions of Yoga. Other “styles” of modern Yoga are simply gross distortions. Traditional yoga has historically been taught orally, and there are subtle nuances among various lineages and teachers, rather than there being someone, precisely agreed upon “yoga”. Principles are usually communicated in sutra style, where brief outlines are expanded upon orally. For example, yoga is outlined in 196 sutras of the Yoga Sutras and then is discussed with and explained by teacher to student. Similarly, the great depth of meaning of Om mantra is expanded upon orally.

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Traditional yoga:

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Modern yoga:

The modern yoga widely practiced around the world today is derivative of Hatha Yoga, although it places a greater emphasis on asana (physical postures) than is found in traditional Hatha Yoga and includes innovations from Indian and foreign sources that are not to be found in traditional teachings on Hatha Yoga.

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Modern yoga is based on five basic principles that were created by Swami Sivananda.

1. Savasana or proper relaxation;

2. Asanas or proper exercise;

3. Pranayama or proper breathing;

4. Proper diet; and

5. Dhyana or positive thinking and Meditation

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In spite of the immense popularity of postural yoga worldwide, there is little or no evidence that asana (excepting certain seated postures of meditation) has ever been the primary aspect of any Indian yoga practice tradition… The primacy of asana performance in transnational yoga today is a new phenomenon that has no parallel in premodern times. The mere fact that one might do a few stretches with the physical body does not in itself mean that one is headed towards that high union referred to as Yoga. Many people work with diet, exercise and interpersonal relationships. This may include physical fitness classes, food or cooking seminars, or many forms of personality work, including support groups, psychotherapy, or confiding with friends. When done alone, these are not necessarily aimed towards Yoga, and are therefore not Yoga, however beneficial they may be. Yet, work with body, food, and relationships may very much fall under the domain of Yoga, when Yoga is the goal. The key is the goal or destination one holds in the heart, mind, and conviction. Without that being directed towards the state of Yoga, the methods can hardly be called Yoga. The goal of Yoga is Yoga, which has to do with the realization in direct experience of the highest unity of our being.

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Perception has recently shifted: The typical perception of Yoga has shifted a great deal in the past century, particularly the past couple decades. Most of this is due to changes made in the West, particularly in the United States, though it is not solely an American phenomenon. The gist of the shift can be summarized in two perspectives, one of which is modern and false, and the other of which is ancient and true.

•False: Yoga is a physical system with a spiritual component.

•True: Yoga is a spiritual system with a physical component.

The false view spreads: Unfortunately, the view that Yoga is a physical exercise program is the dominant viewpoint. The false view then spreads through many institutions, classes, teachers, books, magazines, and millions of students of modern Yoga, who have little or no knowledge or interest in the spiritual goals of ancient, authentic, traditional Yoga and Yoga Meditation.

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This is not yoga:

The misuse of the word Yoga often involves what logicians call the Fallacy of Composition. One version of the Fallacy of Composition is projecting a characteristic assumed by a part to be the characteristic assumed by the whole or by others. It may lead to false conclusion that whenever a person is doing some action that is included in Yoga, that person is necessarily doing Yoga. Here are some obviously unreasonable and false arguments about the nature of Yoga. These are given as examples of the absurdity of the fallacy of composition.

•Body flexing is part of Yoga; therefore, anybody who flexes the body is practicing Yoga.

•Breath regulation is part of Yoga; therefore, anybody who intentionally breathes smoothly and slowly is practicing Yoga.

•Cleansing the body is part of Yoga; therefore, anybody cleansing the body is practicing Yoga.

•Concentrating the mind is part of Yoga; therefore anybody who concentrates is practicing Yoga.

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Asana, pranayama and meditation:

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Asana:

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Asanas are various body positions designed to improve health and remove diseases in the physical, causal, and subtle bodies. The word “asana” is Sanskrit for “seat”, which refers not only to the physical position of the body but also to the position of the body in relation to divinity. They were originally meant for Meditation, as the postures can make you feel relaxed for a long period of time. The regular practice of Asanas will grant the practitioner muscle flexibility and bone strength, as well as non-physical rewards such as the development of will power, concentration, and self-withdrawal. Asana is defined as “posture or pose;” its literal meaning is “seat.” Originally, there was only one asana– a stable and comfortable pose for prolonged seated meditation.  Asana practice alone is shown to have a myriad of health benefits from lowering blood pressure, relief of back pain and arthritis, and boosting of the immune system. Increasingly, many believe asana practice to reduce Attention Deficit Disorder (AD/HD) in children, and recent studies have shown it improves general behavior and grades.

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And while practicing asana for improved health is perfectly acceptable, it is not the goal or purpose of yoga. Perhaps the two most influential yoga gurus of our time, BKS Iygenar and Pattabhi Jois were clear about the intended purpose of asana. In interviews from 2004, re-published by Namarapa magazine in Fall 2014 issue, the two masters are quoted as follows:

“Asanas are not meant for physical fitness, but for conquering the elements, energy, and so on. So, how to balance the energy in the body, how to control the five elements, how to balance the various aspect of the mind without mixing them all together, and how to be able to perceive the difference between the gunas, and to experience that there is something behind them, operating in the world of man – that is what asanas are for. The process is slow and painstaking, but a steady inquiry facilitates a growing awareness.” – Iyengar

“But using it [yoga] for physical practice is no good, of no use – just a lot of sweating, pushing, and heavy breathing for nothing. The spiritual aspect, which is beyond the physical is the purpose of yoga. When the nervous system is purified, when your mind rests in the atman [the Self], then you can experience the true greatness of yoga. To practice asana and pranayama is to learn to control the body and the senses, so that the inner light can be experienced. That light is the same for the whole world.” – Jois

Still, both yoga masters recognized the importance of asana as vital and necessary to the practice of yoga. Asana is the limb through which most people enter the world of yoga, and its importance should not be diminished. Higher levels of yoga cannot be achieved if the physical body is weak, sick, or injured. Asana, when practiced under the guidance of a guru or an experienced and properly trained teacher, is integral to yoga. Unfortunately, the likes of Iygenar and Jois are difficult to come by, especially in much of today’s yoga culture which is driven by a Western-mentality of commercialization and commodification. Without such insight, wisdom, and proper guidance, modern day “yoga” is asana without understanding, faith, or intention, and therefore, merely remains at the level of physical exercise. In a 2005 interview published in Namarupa magazine, Prashant Iyengar, son of B.K.S. Iyengar, shared a similar view when he said, “We cannot expect that millions are practicing real yoga just because millions of people claim to be doing yoga all over the globe. What has spread all over the world is not yoga. It is not even non-yoga; it is un-yoga.”

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Ideal time to start these asanas is in the morning. Morning times are quiet and conducive to perform asanas. The most important thing to bear in mind is to be aware or conscious of what one is doing during the asana practice. Inattention during the practice does not give favorable results. The aim is to observe, recognize and control the bodily movements. Yoga is one of the best means to understand the nature of the mind, body language and above all, self-study. Asanas are 80 percent mental and 20 percent physical. A regular routine should be adhered to, while following asana practice. While doing the asanas, one should be conscious of the stretch in the limbs and be aware of the flexibility of the joints. A general yoga routine should commence with padmasana, a sitting posture suitable for meditation. Apart from being conscious of bodily movements, one should start to observe breathing, heartbeat and the tension in the muscles. One must be able to distinguish the different states of tension, relaxation and other sensations in the body. The main emphasis of these asanas is, to assume a posture slowly, smoothly, and to be aware of the feelings that the posture helps to develop. The posture should be executed in a slow and controlled manner. Then focus should be on breathing. Controlled breathing helps to gain conscious control over bodily functions. Then one should relax into the posture. Relaxation is an important aspect in yoga practice. One should mentally tune oneself into yoga postures or visualize the posture one is going to practice. All the muscles must be in a relaxed position from the start to the final position, and practicing yoga makes one feel good. They should be executed in a slow, harmonious and continuous manner. To achieve a perfect posture should not be the aim, but rather one should have a non-striving attitude. Observation and concentration play a vital role. Introspection of one’s own thoughts and feelings too play a significant role. When thoughts invade the mind, they should be gently pushed away and attention should be gathered gently. Each yoga posture, which falls into phases, manifests itself in synchrony. One must listen to the body and should not stretch oneself beyond one’s capacity. Always do it in a relaxed and calm manner. The essence of yoga is to transform life into a healthy one. It changes and normalizes the incorrect pattern of living. Yoga re-energizes the mind and body.

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The different postures or asanas include:

•lying postures

•sitting postures

•standing postures

•inverted or upside-down postures

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Asana is one of the eight limbs of classical Yoga, which states that poses should be steady and comfortable, firm yet relaxed helping a practitioner to become more aware of their body, mind, and environment. The 12 basic poses or asanas are much more than just stretching. They open the energy channels, chakras and psychic centers of the body while increasing flexibility of the spine, strengthening bones and stimulating the circulatory and immune systems. Along with proper breathing or pranayama, asanas also calm the mind and reduce stress.

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12 basic asanas:

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Yoga poses with animal names:

There are many yoga poses with animal names. It’s only natural, as the early yogis were influenced by what was around them. Animals have been instinctively practicing asana (yoga poses) for centuries.  In fact, many of the yoga poses we have come to know in class were named after animals both for the resemblance itself, and for the quality of the animal itself. Ancient yogis observed animals in nature; their abilities and beauty. To emulate these animal qualities through asana was considered a high sign of spiritual enlightenment. Along with the dog, this asana menagerie includes other mammals (cow, camel, cat, horse, lion, monkey, bull), birds (eagle, peacock, goose or swan, crane, heron, rooster, pigeon, partridge), a fish and a frog, reptiles (cobra, crocodile, tortoise), and arthropods (locust, scorpion, firefly). There’s even a pose named after a mythic sea monster, the makara, the Hindu zodiac’s Capricorn, which is pictured as having the head and forelegs of a deer and the body and tail of a fish.

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Padmasana:

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Padmasana is a term derived from sanskrit word padma: lotus, and asana: seat or throne. While doing any asana, it is very important to be alert and be conscious of what we are doing. Concentration and relaxation play a vital role in the practice of yoga. Padmasana is also called kamalasana, which means lotus. The form of the legs while performing this asana gives the appearance of a lotus. It is the best asana for contemplation. As we start the asana, one must become conscious of the body. We must try to visualize the posture one is going to practice. This is actually a form of mental tuning. So we have to visualize before doing the asana. As one takes the right posture, one must close the eyes and be aware of the body. The Muscles must be relaxed. One should feel the touch of the legs on the floor. The focus should then be shifted to the breath. A feeling of peace touches the mind. Sit in this posture for a few Minutes before proceeding to the next asana.

Steps to follow for Padmasana:

1. Sit on the ground by spreading the legs forward.

2. Place the right foot on the left thigh and the left foot on the right thigh.

3. Place the hands on the knee joints.

4. Keep the body, back and head erect.

5. Eyes should be closed.

6. One can do Pranayama in this asana.

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Mudra:

A mudra is a symbolic or ritual gesture in Hinduism and Buddhism. While some mudras involve the entire body, most are performed with the hands and fingers. In yoga, mudras are used in conjunction with pranayama (yogic breathing exercises), generally while seated in Padmasana, Sukhasana or Vajrasana pose, to stimulate different parts of the body involved with breathing and to affect the flow of prana in the body. The yoga teacher Satyananda Saraswati, founder of the Bihar School of Yoga, continued to emphasize the importance of mudras in his instructional text Asana, Pranayama, Mudra, Bandha.

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Savasana (The Corpse Pose):

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The Corpse Pose or Savasana is the classic relaxation pose, practised before each session, between asanas, and in Final

Relaxation. It looks deceptively simple, but it is in fact one of the most difficult asanas to do well and one which changes and develops with practice. At the end of an asana session your Corpse Pose will be more complete than at the beginning because the other asanas will have progressively stretched and relaxed your muscles. When you first lie down, look to see that you are lying symmetrically as symmetry provides proper space for all parts to relax. Now start to work into the pose. Rotate your legs in and out then let them fall gently out to the sides. Do the same with your arms. Rotate the spine by turning your head from side to side to centre it. Then start stretching yourself out, as though someone were pulling your head away from your feet, your shoulders down and away from your neck, your legs down away from your pelvis. Let gravity embrace you. Feel your weight pulling you deeper into relaxation, melting your body into the floor. Breathe deeply and slowly from the abdomen (right), riding up and down on the breath, sinking deeper with each exhalation. Feel how your abdomen swells and falls. Many important physiological changes are taking place, reducing the body’s energy loss, removing stress, lowering your respiration and pulse rate, and resting the whole system. As you enter deep relaxation, you will feel your mind grow clear and detached.

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Yoga series (dynamic asana):

Yoga series consist of asanas done in sequence. The most common yoga series is Surya Namaskara or the Sun Salutation originating in the Hatha Yoga system. Ashtanga yoga (power yoga), Vinyasa Yoga and Bikram yoga are also considered as yoga series.

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Ashtanga yoga:

Ashtanga is based on ancient yoga teachings, but it was popularized and brought to the West by Pattabhi Jois in the 1970s. It’s a rigorous style of yoga that follows a specific sequence of postures and is similar to vinyasa yoga, as each style links every movement to a breath. The difference is that ashtanga always performs the exact same poses in the exact same order. This is a hot, sweaty, physically demanding practice.

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Vinyasa Yoga:

Vinyasa means flow in Sanskrit. In this practice of yoga vinyasas are completed between poses to refresh the body and prepare for the next posture. A vinyasa typically consists of chattaranga, followed by a cobra/ upward dog position into a downward dog. Downward dog is considered to be the restorative posture and is a resting pose to regain the ujjayi breath before moving on to the next posture.

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Bikram Yoga:

Bikram Yoga is a style of yoga developed by Bikram Choudhury and a Los Angeles, California based company. Bikram Yoga is ideally practiced in a room heated to 105 °F (40.5 °C) with a humidity of 40%, and classes, which are 90 minutes long, are a guided series of 26 postures and two non-pranamic breathing exercises.

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Surya Namaskara:

Sanskrit for Sun Salutation owes its name for expressing devotion (bhakti) to Surya, the solar deity in the Hindu pantheon, by concentrating on the Sun. The Sun Salutation is, for many yogis, an exercise to be performed at sun rise, or at least in the morning. Surya Namaskara is a sequence of twelve asanas, where the five beginning asanas are the same as the last five asanas of the sequence. The Sun Salutation can be practiced at varying levels of awareness, ranging from that of physical exercise, to a complete sadhana which incorporates asana, pranayama, mantra and chakra meditation.

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Yoga and breathing:

Breathing is one of the most important parts of yoga. Breathing steadily while you’re in a yoga pose can help you get the most from the pose. But practicing breathing exercises when you’re not doing yoga poses can be good for you, too. It may seem strange to practice breathing, since we do it naturally every moment of our lives. But when people get stressed, their breathing often becomes shallower and more rapid. Paying attention to how you are breathing can help you notice how you’re feeling — it can give you a clue that you’re stressed even when you don’t realize it. So start by noticing how you’re breathing, then focus on slowing down and breathing more deeply.

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The Importance of breath in Yoga:

Awareness of breath and synchronizing breath and movement is what makes yoga, yoga; and not gymnastics or any other physical practice. When focusing on the breath during our asana practice, the control of the breath shifts from the brain stem (medulla oblongata) to the cerebral cortex (evolved part of brain) due to us being aware of the breath. It’s in that moment, when we are aware, when the magic starts to happens. The mind will become quieter and a calm awareness arises.  As a result emotional stress and random thoughts are less likely to occur. So basically the whole system gets a break. The energy, the prana, begins to flow more freely pushing through any emotional and physical blockages and thus freeing the body and mind which results in the “feel good” effect after a yoga practice. So we can safely say that breath has an intimate relationship to the overall movement of prana (life energy) throughout the entire body. Those who have practiced some serious meditation have apparently noticed and seen that when the breath moves, the mind moves as well. Of course this works both ways so as the mind moves, the breath moves too. This basically means that the breath gives us a tool with which we can explore the subtler structures of our mental and emotional worlds. When the breath changes, that tells you that something is happening in your mind. When something happens in your mind, like a disturbing thought for example, your breath will reflect that back to you. You will then understand that, because the breath and mind are so connected, awareness and mindfulness of breathing can lead to insight into the nature of mind. Insight into the nature of the mind leads eventually to freedom from suffering.

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Accurate use of the breath adds an important dimension to the practice of asanas. It brings both physical and mental refinement and leads naturally and easily to the practice of yogic breathing or pranayama. For thousands of years, yogis have realized the profound relationship between one’s mental state and one’s breathing. When we are nervous, frightened, or angry, our breathing is immediately affected, usually becoming short, fast, and shallow. Conversely, when we are relaxed and calm, our breathing is long, slow, and deep. Thus, our breathing often reflects our mental condition. If we consciously develop slow, calm, deep breathing, one result is a relaxed mind. Although the final aim of yogic breathing is not simply to calm the mind, this is an essential first step.

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While priorities may differ between styles and teachers, when to inhale and exhale during asana is a fairly standardized practice element. Here three simple guidelines are offered for pairing breath with types of poses.

1. When bending forward, exhale.

When you exhale, the lungs empty, making the torso more compact, so there is less physical mass between your upper and lower body as they move toward each other. The heart rate also slows on the exhalation, making it less activating than an inhalation and inducing a relaxation response. Since forward bends are typically quieting postures, this breathing rule enhances the energetic effects of 
the pose and the depth of the fold.

2. When lifting or opening the chest, inhale.

In a heart-opening backbend, for instance, you increase the space in your chest cavity, giving the lungs, rib cage, and diaphragm more room to fill with air. And heart rate speeds up on an inhalation, increasing alertness and pumping more blood to muscles. Deep inhalation requires muscular effort that contributes to its activating effect. Poses that lift and open the chest are often the practice’s energizing components, so synchronizing them with inhalations takes optimum advantage of the breath’s effects on the body.

3. When twisting, exhale.

In twists, the inhalation accompanies the preparation phase of the pose (lengthening the spine, etc.), and the exhalation is paired with the twisting action. Posturally, that’s because as your lungs empty there’s more physical space available for your rib cage to rotate further. But twists are also touted for their detoxifying effects, and the exhalation is the breath’s cleansing mechanism for expelling CO2.

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Belly Breathing:

Belly breathing allows you to focus on filling your lungs fully. It’s a great way to counteract shallow, stressed-out breathing:

•Sit in a comfortable position with one hand on your belly.

•With your mouth closed and your jaw relaxed, inhale through your nose. As you inhale, allow your belly to expand. Imagine the lower part of your lungs filling up first, then the rest of your lungs inflating.

•As you slowly exhale, imagine the air emptying from your lungs, and allow the belly to flatten.

•Do this 3-5 times.

This kind of breathing can help settle your nerves before a big test, sports game, or even before bed.

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Yoga and diaphragm:

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The diaphragm is one of the most unique muscles in the body and serves as the crucial actor in one of its most essential functions: breathing. What we might not always realize is that the diaphragm holds great significance beyond its essential role in facilitating the rhythm of breath. Unique in both form and function, the diaphragm creates an umbrella-like dome that sits over the abdominal organs, attaching to the inner surface of the ribs and lumbar vertebrae. When we inhale, the diaphragm flattens downward, putting gentle pressure on the belly’s organs, creating a vacuum that pulls air into the lungs. When we exhale, the diaphragm relaxes, releasing pressure on the organs, allowing the lungs to deflate. Without the diaphragm’s presence, the lungs would remain lifeless pieces of tissue. But with the magic of this special muscle’s movements, the lungs come to life and fill with oxygen for the body to use. On a physical level, this the diaphragm critically assists the body in the inhalation of oxygen and exhalation of carbon dioxide. On an energetic level, this process has deeper meaning. The act of breathing is evidence of our interdependent relationship with the world beyond ourselves. While breathing, we receive the oxygen from our environment and, in turn, offer carbon dioxide back out where it is absorbed by plants, trees and other microorganisms. From this perspective, breathing is more than just an act of individual survival; it is part of the ongoing processes of co-creation and communion with the world we inhabit. The yogi sees this process as an ongoing exchange of prana—the universal life force which flows through us all, driving our every action and sustaining life on our planet. This continuous exchange begins with our very first breath of life and ends with the last. From the moment we are born to the moment we transition, our breath is vital in making the world go round. For this remarkable act of interconnectedness, we have the diaphragm to thank. The unique muscle is located within the realm of the fourth chakra—anahata, the heart chakra (vide infra). This is the place in the body where primal and self-centric instincts begin to drive us toward connections with others, taking us beyond our physical, emotional and mental bodies. Additionally, the fourth chakra and diaphragm reside at the half-way point between the crown chakra and the first chakra regions. The inferior (lower) bodily functions are innately primitive, and the superior (upper) functions are esoteric and intellectual. The region of the fourth chakra then, becomes the point of balance between what exists within (for us personally) and our outward environment. Our ability to interact with the world and the quality of those interactions are evident in the way we breathe. The diaphragm, incredibly powerful yet sensitive enough to detect the subtleties of life, bears the imprints of any emotional, energetic and physical disturbances or highlights we experience. For instance, when we are tense, we tend to shorten or quicken the breath, but when we are relaxed or at ease, our breath is slower and more rhythmic. The breath can be considered a storehouse of memories, showcasing our interactions and personal habits in our breathing patterns.

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Pranayama:

Pranayama is derived from the words “prana” (life-force or energy source) and “ayama” (to control). It is the science of breath control. This is an important part of Hatha Yoga because the yogis of old times believed that the secret to controlling one’s mind can be unlocked by controlling one’s breath. The practice of Pranayama can also help unleash the dormant energies inside our body. Pranayama is the fourth ‘limb’ of the eight limbs of Ashtanga Yoga mentioned in verse 2.29 in the Yoga Sutras of Patanjali. Many yoga teachers advise that pranayama should be part of an overall practice that includes the other limbs of Patanjali’s Raja Yoga teachings, especially Yama, Niyama, and Asana. The aim of pranayama is to inspire. infuse, control, regulate and balance the Prana Shakti (vital energy) in the body. You can do Pranayama 3 to 4 hours after meals. The most suitable and useful time for Pranayama is the morning hours on an empty stomach.

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Our breath has a profound impact on our physiological states. Using breath to address imbalances of the nervous system is a very effective and powerful way to cultivate sattva. For example, did you know that simply extending the length of your exhales beyond the length of your inhales stimulates your parasympathetic nervous system (the “calm down” mechanism in your body)?  On the other hand, taking breaths where your inhales are longer than your exhales has a stimulating (or rajasic) effect. Depending on how your body is feeling (overly stimulated or overly inert), you can choose the breath that brings you closer to balance.

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Pranayama is the method of breath control. Proper breathing and awareness of the breath is very important. Swami Yogananda says, “Breath is the cord that ties the soul to the body”. Your breathing directly affects the mental states. Breathing exercises help to control bodily functions. A regular, deep breath enables one to feel calm and an irregular breath can make you feel anxious. Yoga Breathing helps to re- charge the cells in the body and re- energizes the brain cells; thus, the body is rejuvenated. Pranayama involves exhalation or rechaka pranayama, inhalation or puraka pranayama and retention of breath or kumbakha pranayama.  It is a powerful tool to combat stress. Our mental states, feelings and bodily sensations affect the pattern of breathing. Positive thoughts cause regular breathing and negative thoughts cause uneven breathing. Correspondingly, in this stress filled lifestyle, it becomes imperative to practice yoga, correctly. Swami Svatmarama says, “By the faulty practice of pranayama the aspirant invites all kinds of ailments”. The aspirant should study the capacity of his lungs before embarking on the practice of pranayama. If he indulges in the wrong practice of pranayama, it will sap him of his energy. A wrong course of breath or over -enthusiasm could result in coughs, asthma, headaches, eye and ear pain.

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Types of Pranayama:

•Quiet Breathing , Deep Breathing , Fast Breathing

• Tribandha and Pranayama

• Nadi Shuddhi Pranayama (Alternate nostril breathing – I)

•Anuloma – Viloma (Alternate Nostril Breathing – II)

•Suryan Bhedan Pranayama (Right Nostril Breathing)

• Ujjayi Pranayama

• Bhramari Pranayama

• Pranayama from Hatha Yoga

Surya Bhedan, Bhasrika, Ujjayi, Shitali, Sitkari, Bhramari, Murchha & Plavini Pranayama

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Nadi Shodhana Pranayama (Alternate-Nostril Breathing):

This breath technique can help you feel more balanced and calm:

•Sit in a comfortable position.

•Place the thumb of your right hand on your right nostril. Tuck your first and middle fingers down and out of the way.

•As your right thumb gently closes your right nostril, slowly exhale through your left nostril, as you count to 5.

•Now, keeping your right thumb on the right nostril, slowly inhale through the left nostril, as you count to 5.

•Lift your thumb, use your ring finger to close your left nostril, and exhale through your right nostril for 5 counts. Then inhale through your right nostril as you slowly count to 5.

•Change back to putting your thumb over your right nostril. Lift your ring finger from your left nostril, and repeat the whole process — exhaling through your left nostril for 5 counts, then inhaling through the left nostril for 5 counts.

•Continue this pattern (exhale, inhale, change sides) for three more cycles.

This practice of alternating between the right and left nostrils as you inhale and exhale unblocks and purifies the nadis, which in yogic belief are energy passages that carry life force and cosmic energy through the body. While there is no clear scientific evidence to support these effects, one pilot study found that within seven days of practicing this technique, overactive nervous systems were essentially rebalanced.

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Ujjayi Pranayama (Victorious Breath or Ocean Breath):

This classic pranayama practice, known for its soft, soothing sound similar to breaking ocean waves, can further enhance the relaxation response of slow breathing, says Patricia Gerbarg, MD, assistant clinical professor of psychiatry at New York Medical College and co-author of The Healing Power of the Breath. Her theory is that the vibrations in the larynx stimulate sensory receptors that signal the vagus nerve to induce a calming effect.  Inhale through your nose, then open your mouth and exhale slowly, making a “HA” sound. Try this a few times, then close your mouth, keeping the back of your throat in the same shape you used to make the “HA,” as you exhale through the nose.

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Kumbhaka Pranayama (Breath Retention):

If you inhale fully and then wait 10 seconds, you will 
be able to inhale a bit more. Holding your breath increases pressure inside the lungs and gives them time to fully expand, increasing their capacity. As a result, the blood that then travels to the heart, brain, and muscles will be more oxygenated. Inhale, inflating the lungs as fully as possible. Hold the breath for 10 seconds. After 10 seconds, inhale a little more. Then hold it for as long as you can.

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Kapalabhati Pranayama (Breath of Fire or Skull-Shining Breath):

This rapid breathing technique is energizing, and activates the sympathetic nervous system. In a study using EEG electrodes to measure brain activity, researchers found that Kapalabhati Pranayama increased the speed of decision-making in a test requiring focus. However for people already under stress, Breath of Fire is not a good idea because you’re throwing gasoline on the fire. To start, take a full, deep inhale and exhale slowly. Inhale again, and begin exhaling by quickly pulling in the lower abs to force air out in short spurts. Your inhalation will be passive between each active, quick exhalation. Continue for 25–30 exhalations.

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Meditation in yoga:

Yoga meditation is not actually a separate aspect of Yoga, due to the fact that Yoga is meditation. However, the phrase Yoga Meditation is being used here to discriminate between Yoga Meditation and the now popular belief that Yoga is about physical postures. Yoga or Yoga Meditation is a complete process unto itself, only a small, though useful part of which relates to the physical body. In the Yoga Meditation of the Himalayan tradition, one systematically works with senses, body, breath, the various levels of mind, and then goes beyond, to the center of consciousness.

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An ordinary person may consider meditation as a worship or prayer. But it is not so. Meditation means awareness. Whatever you do with awareness is meditation. “Watching your breath” is meditation; listening to the birds is meditation. As long as these activities are free from any other distraction to the mind, it is effective meditation. Meditation is not a technique but a way of life. Meditation means ‘a cessation of the thought process’. It describes a state of consciousness, when the mind is free of scattered thoughts and various patterns. The observer (one who is doing meditation) realizes that all the activity of the mind is reduced to one.

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Traditionally, the classical yoga texts, describe that to attain true states of meditation one must go through several stages. After the necessary preparation of personal and social code, physical position, breath control, and relaxation come the more advanced stages of concentration, contemplation, and then ultimately absorption. But that does not mean that one must perfect any one stage before moving onto the next. The Integral yoga approach is simultaneous application of a little of all stages together. Commonly today, people can mean any one of these stages when they refer to the term meditation. Some schools only teach concentration techniques, some relaxation, and others teach free form contemplative activities like just sitting and awaiting absorption. Some call it meditation without giving credence to yoga for fear of being branded ‘eastern’. But yoga is not something eastern or western as it is universal in its approach and application. With regular practice of a balanced series of techniques, the energy of the body and mind can be liberated and the quality of consciousness can be expanded. This is not a subjective claim but is now being investigated by the scientists.

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Benefits of meditation:

- Stress relief

- Lowers high blood pressure and tension-related pain like headaches, insomnia, ulcers and joints pain too.

- Improves the mood, immunity, alertness and energy.

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Sahaja yoga and mental silence:

Sahaja yoga meditation has been shown to correlate with particular brain and brain wave activity.  Some studies have led to suggestions that Sahaja meditation involves ‘switching off’ irrelevant brain networks for the maintenance of focused internalized attention and inhibition of inappropriate information.  A study comparing practitioners of Sahaja Yoga meditation with a group of non meditators doing a simple relaxation exercise, measured a drop in skin temperature in the meditators compared to a rise in skin temperature in the non meditators as they relaxed. The researchers noted that all other meditation studies that have observed skin temperature have recorded increases and none have recorded a decrease in skin temperature. This suggests that Sahaja Yoga meditation, being a mental silence approach, may differ both experientially and physiologically from simple relaxation. Sahaja meditators scored above peer group for emotional wellbeing measures on SF-36 ratings.

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Kundalini yoga:

Kundalini yoga is the science of liberating the dormant potential energy in the base of the spine (kundalini). The definition of yoga in kundalini yoga is the union of the mental current (ida) and the pranic current (pingala) in the third eye (ajna chakra) or at the base chakra (muladhara chakra). This unifies duality in us by connecting body and mind, and leads to the awakening of spiritual consciousness.  Kundalini yoga meditation research has found that there “appears to produce structural as well as intensity changes in phenomenological experiences of consciousness”, and that multiple regions of the brain are active.

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Other types of meditation besides yoga:

There are different meditative techniques to suit different purposes:

- Mindful meditation

- Reflective meditation

- Mantra mediation

- Focused meditation

- Visualisation meditation

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One of the most fascinating studies published on meditation is one from several years ago — but one that is good to keep in mind if you’re interested in mental health and brain plasticity. The study, led by Harvard researchers at Massachusetts General Hospital (MGH), found that meditating for only 8 weeks actually significantly changed the brain’s grey matter — a major part of the central nervous system that is associated with processing information, as well as providing nutrients and energy to neurons. This is why, the authors believe, that meditation has shown evidence in improving memory, empathy, sense of self, and stress relief. “Although the practice of meditation is associated with a sense of peacefulness and physical relaxation, practitioners have long claimed that meditation also provides cognitive and psychological benefits that persist throughout the day,” Dr. Sara Lazar, a Harvard Medical School instructor in psychology said. “This study demonstrates that changes in brain structure may underlie some of these reported improvements and that people are not just feeling better because they are spending time relaxing.” In the study, 16 participants took a Mindfulness-Based Stress Reduction program for 8 weeks. Before and after the program, the researchers took MRIs of their brains. After spending an average of about 27 minutes per day practicing mindfulness exercise, the participants showed an increased amount of grey matter in the hippocampus, which helps with self-awareness, compassion, and introspection. In addition, participants with lower stress levels showed decreased grey matter density in the amygdala, which helps manage anxiety and stress. “It is fascinating to see the brain’s plasticity and that, by practicing meditation, we can play an active role in changing the brain and can increase our well-being and quality of life,” Dr. Britta Holzel, an author of the study said.

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Relaxation vis-à-vis meditation:

We often think of watching TV, sitting down with a cocktail or a good book, or simply vegging out as relaxing. But true relaxation is something that is practiced and cultivated; it is defined by the stimulation of the relaxation response. The relaxation response involves a form of mental focusing similar to meditation. Dr. Herbert Benson, one of the first Western doctors to conduct research on the effects of meditation, developed this approach after observing the profound health benefits of a state of bodily calm he calls “the relaxation response.” In order to elicit this response in the body, he teaches patients to focus upon the repetition of a word, sound, prayer, phrase, or movement activity (including swimming, jogging, yoga, and even knitting) for 10-20 minutes at a time, twice a day. Patients are also taught not to pay attention to distracting thoughts and to return their focus to the original repetition. The choice of the focused repetition is up to the individual. Some forms of conscious relaxation may become meditation, and many meditators find that their practice benefits from using a relaxation technique to access an inner stillness helpful for meditating. But while relaxation is a secondary effect of some meditation, other forms of meditation are anything but relaxing. Ultimately, it all comes down to the intention and purpose of the technique. All conscious relaxation techniques offer the practitioner a method for slowly relaxing all the major muscle groups in the body, with the goal being the stimulation of the relaxation response; deeper, slower breathing and other physiological changes help the practitioner to experience the whole body as relaxed.

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Types and styles of yoga:

Yoga comes in many forms, but most classes contain two core components: poses and breathing. Poses are the different movements of yoga, ranging in difficulty from simply lying flat to physically challenging postures. As you perform the poses, you’ll carefully control your breathing and, depending on the type of yoga, meditate or chant. Hatha yoga is the basic form, slow-paced and suited for beginners. Other variations of yoga include the faster-paced ashtanga; Iyengar, which uses items such as straps or chairs to help with the poses; kundalini, which focuses heavily on chants and meditation; and Bikram, which you perform in a heated room.

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Modern forms of yoga have evolved into exercise focusing on strength, flexibility, and breathing to boost physical and mental well-being. There are many styles of yoga, and no style is more authentic or superior to another; the key is to choose a class appropriate for your fitness level. Classes should be chosen depending on your fitness level and how much yoga experience you have. Types and styles of yoga may include:

•Ashtanga yoga: based on ancient yoga teachings but popularized in the 1970s, each of the six established sequences of postures rapidly link every movement to breath. This physically challenging style consists of an unvarying sequence of poses. Typically, you execute 70 poses in one 90-minute to two-hour session.

•Bikram yoga: held in artificially heated rooms at temperatures of nearly 105 degrees and 40% humidity, Bikram is a series of 26 poses and sequence of two breathing exercises. Founder Bikram Choudhury popularized this style of “hot yoga” in the 1970s. To mimic the climate in Choudhury’s hometown in northern India, studios are heated to a saunalike 105 degrees Fahrenheit, with a 40 percent humidity level. The heat loosens your muscles, increasing your ability to stretch.  Each 90-minute class includes a series of 26 poses done twice through, sandwiched between two sessions of breath work (think rapid inhalations and exhalations).

•Hatha yoga: a generic term for any type of yoga that teaches physical postures. When a class is labelled as “hatha,” it is usually a gentle introduction to the basic yoga postures.

•Iyengar yoga: focused on finding the proper alignment in each pose and using props such as blocks, blankets, straps, chairs and bolsters to do so.

•Jivamukti yoga: meaning, “liberation while living,” jivamukti yoga emerged in 1984, incorporating spiritual teachings and vinyasa style practice. Each class has a theme, which is explored through yoga scripture, chanting, meditation, asana, pranayama, and music, and can be physically intense.

•Kripalu yoga: teaches practitioners to get to know, accept and learn from the body. In a Kriplau class, each student learns to find their own level of practice on a given day by looking inward. The classes usually begin with breathing exercises and gentle stretches, followed by a series of individual poses and final relaxation.

•Kundalini yoga: the Sanskrit word kundalini means coiled, like a snake. Kundalini yoga is a system of meditation directed toward the release of kundalini energy. A 90-minute class typically begins with chanting and ends with singing, and in between features asana, pranayama, and meditation designed to create a specific outcome. Expect to encounter challenging breathing exercises, including the rapid pranayama known as Breath of Fire, mini-meditations, mantras, mudras (sealing gestures), and vigorous movement-oriented postures, often repeated for minutes, that will push you to your limit—and beyond. This form of yoga was developed to calm the mind and energize the body through movement, the chanting of mantras, and breathing. The average session is made up of 50 percent exercise, 20 percent breath work, 20 percent meditation, and 10 percent relaxation. The goal is to release the energy that kundalini devotees believe is stored at the base of the spine.

•Power yoga: an active and athletic style of yoga adapted from the traditional ashtanga system in the late 1980s.

•Prenatal yoga: yoga postures carefully adapted for expectant mothers. Prenatal yoga is tailored to help women in all stages of pregnancy or assist with getting back in shape post-birth.

•Restorative yoga: a relaxing method of yoga, spending a class in four or five simple poses using props like blankets and bolsters to sink into deep relaxation without exerting any effort in holding the pose.

•Sivananda: a system based on a five-point philosophy that proper breathing, relaxation, diet, exercise, and positive thinking work together to form a healthy yogic lifestyle. Typically uses the same 12 basic asanas, bookended by sun salutations and savasana poses.

•Vinyasa yoga: meaning, “flow,” vinyasa classes are known for their fluid, movement-intensive practices. Classes are often choreographed to have smooth transitions from one pose to another, in an almost dance-like manner.

•Viniyoga: intended to be adaptable to any person, regardless of physical ability, viniyoga teachers much be highly trained and tend to be experts on anatomy and yoga therapy.

•Yin: a quiet, meditative yoga practice, also called taoist yoga. Yin yoga enables the release of tension in key joints: ankles, knees, hips, the whole back, neck, and shoulders. Yin poses are passive, meaning the muscles are to relax and let gravity do the work.

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Kriya yoga:

Kriya Yoga is described by its practitioners as the ancient Yoga system revived in modern times by Mahavatar Babaji through his disciple Lahiri Mahasaya in 1861. The Kriya yoga system consists of a number of levels of Pranayama, mantra, and mudra based on techniques intended to rapidly accelerate spiritual development and engender a profound state of tranquility and God-communion.

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Yoga Nidra (yogic sleep):

Yoga nidra or “yogic sleep” is a sleep-like state which yogis report to experience during their meditations. Yoga nidra, lucid sleeping is among the deepest possible states of relaxation while still maintaining full consciousness. The distinguishing difference is the degree to which one remains cognizant of the actual physical environment as opposed to a dream environment. This is a form of deep relaxation practiced commonly as part of the ashram life in India. This is the ultimate way to relax and may be practiced daily. Under the direction of Dr. Elmer Green in 1971, researchers used an electroencephalograph to record the brainwave activity of an Indian yogi, Swami Rama, while he progressively relaxed his entire physical, mental and emotional structure through the practice of yoga nidra. What they recorded was a revelation to the scientific community. The swami demonstrated the capacity to enter the various states of consciousness at will, as evidenced by remarkable changes in the electrical activity of his brain. Upon relaxing himself in the laboratory, he first entered the yoga nidra state, producing 70% alpha wave discharge for a predetermined 5 minute period, simply by imagining an empty blue sky with occasional drifting clouds. Next, Swami Rama entered a state of dreaming sleep which was accompanied by slower theta waves for 75% of the subsequent 5 minute test period. This state, which he later described as being “noisy and unpleasant”, was attained by “stilling the conscious mind and bringing forth the subconscious”. In this state he had the internal experience of desires, ambitions, memories and past images in archetypal form rising sequentially from the subconscious and unconscious with a rush, each archetype occupying his whole awareness. Finally, the swami entered the state of (usually unconscious) deep sleep, as verified by the emergence of the characteristic pattern of slow rhythm delta waves. However, he remained perfectly aware throughout the entire experimental period. He later recalled the various events which had occurred in the laboratory during the experiment, including all the questions that one of the scientists had asked him during the period of deep delta wave sleep, while his body lay snoring quietly. Such remarkable mastery over the fluctuating patterns of consciousness had not previously been demonstrated under strict laboratory conditions. The capacity to remain consciously aware while producing delta waves and experiencing deep sleep is the ultimate state of yoga nidra in which there are no dreams, but only the deep sleep state with retained consciousness/awareness. The result is a single, semi-enlightened state of consciousness and a perfectly integrated and relaxed personality.  A 2012 study published in the Indian Journal of Physiology and Pharmacology reports yoga nidra may improve blood pressure and heart rate variables in patients with menstrual problems. A recent study published in the Indian Journal of Physiology and Pharmacology found yoga nidra may reduce the symptoms of diabetes and help control blood glucose levels. A pilot study conducted at Walter Reed Army Medical Center reports yoga nidra may help relieve PTSD symptoms in soldiers returning home from wars in Iraq and Afghanistan.

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My view:

Delta sleep is our deepest sleep, the point when our brain waves are least like waking. Consequently, it is most difficult stage in which to wake sleepers, and when they are awakened they are usually sleepy and disoriented. Interestingly, delta sleep is when sleep walking and sleep talking is most likely to occur. Since deep sleep with delta waves is associated with sleep walking and sleep talking, there is some consciousness in it, so delta wave deep sleep cannot be considered as unconscious state. What yoga expert does is to enhance this little consciousness by practice.

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Yoga with fast heart rates:

Most yoga asanas reduces your breath and heart rate.  But three types of Yoga are sure to raise your heart rate.

1.  Bikram yoga

2. Ashtanga yoga or power yoga

3.  Vinyasa yoga

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Which style of Yoga is best for you?

If you’re new to yoga, you have a lot of options. There are many types of yoga to choose from. With any style of yoga, you can improve your strength, flexibility, and balance. And all yoga styles release tension in your body, quiet your mind, and help you relax. To get the most benefit, you should choose a yoga style that matches your current fitness level, as well as your personality and goals for practicing yoga. Try different classes and teachers, and see what works for you. If you’re new to yoga, it’s a good idea to take a few classes in a slower style of yoga first to get the feel for the poses. That’s because there’s less individual attention and more focus on moving through the power yoga class.

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Three questions to consider:

To decide on the yoga style that’s right for you, ask yourself these three questions:

1. Are you doing yoga for fitness and to get in shape as well as to explore the mind-body connection? Then choose a more vigorous yoga style like power yoga, ashtanga yoga, or Bikram yoga. All three styles combine an athletic series of poses into a vigorous, total-body workout.

2. Do you have an injury, a medical condition, or other limitations? Then start with a slower class that focuses on alignment, such as Iyengar yoga, Kripalu yoga, or viniyoga.

3. Are the meditative and spiritual aspects of yoga your primary goal? Then try one of the yoga styles that include plenty of meditation, chanting, and the philosophic aspects of yoga. For example, you might try kundalini yoga.

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Burmese yoga:

Bando Yoga or Burmese Yoga is an ancient yoga system that has existed for many centuries, perhaps over 2,000 years.  Bando Yoga is a form of yoga from Myanmar often taught as an adjunct of the martial art of bando. Composed of three major yoga systems, Bando Yoga was greatly influenced by the internal training of Indian martial arts and Indian Kundalini yoga, Tibetan Tantric yoga and Chinese Chi-Gong (from the southwestern region).  Today it is practiced by ethnic Burmese in parts of Southeast Asia, India and Bangladesh. The purpose of Bando Yoga is to maintain health, prevent injury and restore health when injury has occurred.  Originally, the term “Bando” [around 500 B.C.] represented physical, emotional and spiritual discipline. In ancient times, improvement of one’s health and physical dexterity, management of one’s emotional state and development of one’s spiritual experiences were all part of Bando training. Bando Yoga has been called “peasant yoga” since it was often used by peasants/workers to maintain/ restore/ recover/ rehabilitate their health so they could continue working doing their menial work…digging, lifting and pulling heavy loads, cutting trees, moving stones, building structures, etc. for maintaining and restoring health for practical reasons…not for enlightenment as some yoga styles aspire to. Bando Yoga was also used by monks to maintain and restore health and prevent injury in their daily lives as they trod the jungles and hills of Burma to minister to those in need and to help people survive the daily challenges of their harsh lives.

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Dhanda Yoga [Staff or a stick is used to stretch, align and adjust the body]:

In ancient Sanskrit, the term “Dhanda” means staff or stick. Dhanda is the yoga symbol for the human spine through which Prana (vital energy or Chi) flows. According to ancient yogic tradition, there are vital energy centers Chakras, along the spine. Various yogic postures are practiced to allow free flow of energy in the body. Dhanda Yoga uses a rod to assist in performing various asanas (yogic postures). Traditionally the staff was between 3 to 6 feet long. It was made of bamboo, wood, rattan, vine, or root. The staff enhances the alignment and helps maintain a center axis to twist evenly through the spine. This wringing activates all the muscles along the spine including the abdominals which helps squeeze out the stale air and massages the internal organs.

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Lonji Yoga [9-12 foot long cloth or rope is used to stretch, align and adjust the body]:

Longyi is technically a sheet of cloth worn in Burma, similar to a sarong or lungi.

Lonji Yoga is a yoga system using a long rope to help develop:

1. mobility of the core of the body

2. flexibility of the limbs

3. structural balance

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Power yoga:

As yoga became more popular in the Western world, a lot of people preferred a more vigorous form of yoga rather than its usual gentler and slower versions. The more aggressive format came to be known as power yoga. In the West, different people popularized power yoga, adding their own dimensions to the ancient art.  A poor commercial derivative of Ashtanga yoga, power yoga is essentially an up-tempo aerobic workout, where yoga poses are done faster and in continuation. Apart from temporary weight loss, it has virtually no health benefits. Since power yoga is a widely used term that was never trademarked, individual teachers usually lend their personal interpretation to classes. But the aggressive and physical take on the traditional discipline has upset the karma of the normally tranquil world of yoga. Purists dismiss it as a “commercial, supermarket” version of the practice with competitive elements that contradict yoga’s most basic principles. There have even been claims that, in encouraging beginners to try and push their bodies into quick movements and advanced positions, this and other sport versions are temporarily successfully and actually dangerous because they could cause injury. Doing repetitive asanas and 100 surya namaskars with no emphasis on alignment is a sure-shot way to injury. So, instead of progressing to better health, they actually regress. Many of these classes also bypass the core components of yoga — pranayama (with proper sequence and ratio) and yoga nidra (relaxation) at the end. The idea of relaxation is to allow the blood lactate levels to return to normal. If they remain high, they could set off the stress glands, making your power yoga session a stressful one.

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Strayed yoga styles:

How far yoga strayed from original Indian side?

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1. Yoga with dogs or ‘Doga’:

Doga poses involve lifting the animal in the air or resting it on your stomach as you bend backwards. Choose your pooch with care though, and think again if you have a Great Dane.

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2. Paddleboard yoga:

Learning to balance on one leg is not enough for paddleboard yogis who do it in the ocean or on lakes on a board. Practitioners say it reveals if a person isn’t properly distributing their weight–presumably by depositing the yogi in the water.

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3. Antigravity or aerial yoga:

Like most unconventional fitness trends, antigravity yoga was devised in New York. This variation involves transcending gravity using a hammock attached to the ceiling to aid practice. This is not to be confused with acroyoga, which incorporates gymnastic elements. Both should not be tried at home.

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4. Cold yoga:

Hot yoga is over. The new trend is to do yoga poses outside in sub-zero temperatures. One company, Flow Outside, offers ‘Snowga’ classes—participants walk to a snowy location and bend and stretch wearing snow shoes.

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5. Dance yoga:

A Yoga Centre has introduced ‘Dance Yoga’, which contain simple and special exercised that can reportedly cure complications like joint pain, migraine and even diabetes. This new branch of yoga is taught along with exercises like walking yoga, breathing exercises, meditation plus nature cure, acupuncture and acupressure at Zen Yoga Centre. With music playing in the background, dance yoga would give one a feeling of freshness both to the body and the mind. It is being imparted to people by dividing them into small groups, since it comprises hatha yoga, dyanamic breathing, meditation, diet and counselling. Ideally there should never be music when you practice asanas. Music, especially when it contains words, makes it more difficult to focus on the yoga practice. Also, loud music is innately stressful. Hatha yoga demands a certain involvement of your body, mind, energy and the innermost core. If you want the involvement of that which is the source of creation within you, your body, mind and energy must be absolutely involved. You should approach it with a certain reverence and focus. I wonder how dancing to the tune of music would lead to meditation.

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6. Laughter yoga:

Laughter yoga (Hasyayoga) is a practice involving prolonged voluntary laughter. Laughter yoga is based on the belief that voluntary laughter provides the same physiological and psychological benefits as spontaneous laughter. Laughter is easily stimulated in a group when combined with eye contact, ‘childlike playfulness’ and laughter exercises. Fake laughter quickly becomes real. Laughter Yoga brings more oxygen to the body and brain by incorporating yogic breathing which results in deep diaphragmatic breathing. A handful of small-scale scientific studies have indicated that Laughter Yoga may potentially have some medically beneficial effects, including benefits to cardiovascular health and mood.

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Basics of yoga:

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Practice of yoga involves:

•Physical postures or Asanas.

•Breathing exercises or Pranayama.

•Meditation.

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Who can do yoga?

I’m not flexible—can I do Yoga?

Yes! You are a perfect candidate for yoga. Many people think that they need to be flexible to begin yoga, but that’s a little bit like thinking that you need to be able to play tennis in order to take tennis lessons. Come as you are and you will find that yoga practice will help you become more flexible. Many times those who are not inherently flexible actually benefit from yoga the most. In addition, most yoga poses can be modified for beginners so that everyone can do a version of the poses. Yoga is more than a set of exercises to increase flexibility, however. K. Pattabhi Jois was often quoted as saying, “Do your practice, and all is coming.” Simple wisdom. For yogis to know anything for sure, we must do it. Not argue about it, push it away or call it impossible, but actually engage in the practice and find out for ourselves. Different skills are needed for different yoga poses: some help the practitioner gain strength, others challenge balance, and others train attention and concentration. Yoga is suitable for most adults of any age or physical condition. Because of the nonstrenuous nature of this approach to exercise, even those with physical limitations can find a beneficial routine of Yoga. There are special techniques for those with physical limitations due to age, illness, injury, substance abuse recovery, obesity, or inactivity.  Many Yoga asana are not recommended for women during menstruation, for pregnant women, or for nursing mothers. Regular practice of breathing and meditation, however, is encouraged.

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Can all the yoga techniques be practiced in all age groups?

Although yoga can be practiced in all age groups, some techniques are more suited and desirable for specific age groups. For example, some asanas that involve forward and backward bending are good for children aged 5 to 10 years. At about 10 years of age, the asanas that have an upside down position and deep breathing can be started. Shuddhikriyas should not be practiced every day. They need to be performed as and when required for removal of impurities from the body. However, Kapalabhati Nauli can be done every day. They are generally most suited for people in age group of 20 to 60 years. Relaxation is necessary for all, irrespective of age. People in all age groups can therefore practice meditation regularly. It is desirable that older people avoid asanas that involve excessive stretching, such as the plough pose or halasana. Strenuous poses such as the scorpion or vrischikasana head–stand or shirshasana should also be avoided older people. When yoga is practiced for therapeutic purpose to overcome or cure ailments, other restrictions are necessary. This is why yoga should not be practiced unless you have learned the correct technique from an expert. Children may safely practice meditation and simple breathing exercises as long as the breath is never held.

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Importance of Yoga for Students:

De-Stressed Students:

One of yoga’s primary benefits for adults is the alleviation of stress. Students may be young, but they aren’t immune to stress. Family pressure, financial fears, academic performance standards and peer groups can all take a toll on a student’s psyche and success in school. A study published in the “International Journal of Yoga” in 2009 examined the effect of yoga on academic performance on highly stressed adolescent students. The researchers — from MGN College of Education in Jalandhar, India — found that seven weeks of regularly doing poses, practicing yoga breathing and participating in mediation practice reduced students’ stress levels, which translated into better academic performance. A later study performed by Harvard Medical School researchers and published in the January 2012 issue of the “Journal of Behavioral Health Services and Research” also found that high-school students who participated in yoga instead of traditional physical education offerings for a semester exhibited improvements in mood, anxiety, perceived stress and resilience.

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How to get started:

The best way to get started in Yoga is to either find a qualified teacher or buy a good book or tape. The best way for beginner is to go to a local yoga studio/class. If you’re not comfortable with that, there are tonnes of clips on youtube or you can purchase a DVD. You can even pick up an illustrated book for beginners. The reason I do recommend visiting a yoga studio/class is because there will be an instructor that can properly adjust your yoga poses or show you how to execute it properly. Although you can learn yoga from books and videos, beginners usually find it helpful to learn with an instructor. Classes also offer camaraderie and friendship, which are also important to overall well-being. Everyone’s body is different, and yoga postures should be modified based on individual abilities. Selecting an instructor who is experienced and attentive to your needs is an important first step to a safe and effective yoga practice.  Regardless of which type of yoga you practice, you don’t have to do every pose. If a pose is uncomfortable or you can’t hold it as long as the instructor requests, don’t do it. Good instructors will understand and encourage you to explore — but not exceed — your personal limits. Many of us attend yoga classes to stretch and lengthen our muscles, dreaming of the day our hips may finally allow us to wriggle into a full lotus pose or some other flexi-goal. You should only practise yoga on your own at home after you have learnt the safe and proper way to do the postures. If you don’t do them correctly, you could injure yourself.

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Can you learn yoga from a book?

Today, if you enter any major bookstore, you will find a minimum of 15 to 20 different yoga books. How to learn yoga in seven days, how to become a yogi in 21 days… Many people have caused immense damage to themselves by learning yoga through books. Yoga seems to be very simple, but there is a very subtle aspect to it. It has to be done with perfect understanding and proper guidance. Without this, one can get into deep trouble. A book can inspire you, but it is not meant to teach a practice.

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What are four things people should look for in a prospective yoga teacher?

1. Sincere interest in and care for the student

2. An ability to listen

3. A desire and ability to teach what is appropriate for the student

4. Confidence balanced with a sense of humility

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When it comes to practicing and teaching yoga, it’s not a one size fits all. Yoga teachers vary in approach, style, experience and training. If you’re young and fit, you will be able to handle a wide range of yoga styles and classes. On the other hand, if you’re a 50+ year old male with super tight hamstrings just starting out, it may be better to start with individual yoga sessions with an experienced teacher. The same thing applies if you have any injuries or physical limitations you’re working with. Let your teacher know before the class, and don’t be shy to ask if the class will still be suitable for you. If the teacher isn’t able to offer specific feedback related to your condition, that’s a good indication the teacher might not a good fit for you.

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When to do yoga:

How many times per week should I practice?

Yoga is amazing—even if you only practice for one hour a week, you will experience the benefits of the practice. If you can do more than that, you will certainly experience more benefits. Experts suggest starting with two or three times a week, for an hour or an hour and a half each time. A yoga session usually lasts between 60 and 90 minutes, and involves a series of postures with breath work, and relaxation time at the end of the class. If you can only do 20 minutes per session, that’s fine too. Don’t let time constraints or unrealistic goals be an obstacle—do what you can and don’t worry about it. You will likely find that after a while your desire to practice expands naturally and you will find yourself doing more and more.

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Practicing Yoga outside:

Outdoor yoga is often praised as a special treat, but it can also add a whole new array of challenges to your practice. Unpredictable and uncontrollable temperatures, bugs, noise, uneven or wet ground, and curious bystanders can all make an outdoor practice less than relaxing. Still, getting outside is good for you, and there are steps you can take to make an outdoor yoga practice more enjoyable—beyond just closing your eyes and turning inward.

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Yoga at workplace:

Practicing yoga at the workplace teaches employees to use relaxation techniques to reduce stress and risks of injury on the job. Yoga at the workplace is a convenient and practical outlet that improves work performance by relieving tension and job stress.

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What to wear to yoga:

Proper alignment of yoga postures is important for many types of yoga. Choose clothes that are not too baggy and that help you and your yoga instructor make sure you’re not doing anything harmful to your body. In more physical types of yoga and especially in hot classes, expect to sweat. Wear clothes that dry quickly, wick moisture away, and will keep you as comfortable as possible to get the most out of your yoga class. Fabrics with stretch will help you feel most comfortable as you move from pose to pose. Whatever you choose to wear to class, you should be able to move freely and feel good.

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Yoga pants:

Yoga pants are a type of flexible, form-fitting pants designed for the practice of yoga as well as other physical activities that involve lots of physical movement, bending and stretching. Some of these other activities include martial arts, dancing, pilates, and aerobics. These pants are generally made of cotton, spandex, nylon, polyester or a similarly light and stretchy synthetic material, giving the pants a very smooth and silk-like finish when worn. There are many different colors but the most common type are black, tight-fitted, and have an elastic waistband folded over at the top. Although designed specifically for yoga, the pants are also worn casually by many women.

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Yoga mats:

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Yoga mats are specially fabricated mats used as an aid during the practice of hatha yoga to prevent hands and feet slipping during asana practice. They are also commonly known as non-slip mats, non-skid mats or sticky mats. If you have practiced yoga on the grass, in the sand, or even on a blanket, you know that standing postures require more strength than flexibility. There are definitely benefits to practicing on a mat rather than bare floor, carpet, or earth.

•First and foremost, a mat provides padding, support, and a barrier from the elements. For many people, pressing their palms, knees, elbows, and vertebrae onto the bare ground or floor can be painful. Having additional support enables them to more comfortably perform the pose. Furthermore, it can be especially helpful when practicing on a less-than-clean surface, such as a hotel room carpet.

•Second, a mat can act as a means of absorption if one starts sweating during their practice, as well as a means slipping prevention. This is definitely the case for “hot yoga” classes, where the room is heated. Some people will insist they can’t maintain a downward facing dog pose without a sticky mat. Honestly, for many beginners this is true; however, once you learn proper form and alignment, you can easily practice this pose on many surfaces, even carpet and tile, without the need for a sticky mat.

•Finally, a mat can serve the purpose of transforming any space into a “sacred” one. It becomes a clearly defined area for your practice which can be especially important when practicing at a studio or with a group of people. As you spend more and more time on your mat, it can begin to feel like a welcoming friend. Stepping onto it can help begin your transition into an altered space.

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Yoga blocks:

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Yoga block or brick is one of the most popular yoga props to use in a yoga class. Yoga props were popularized by B.K.S. Iyengar as tools to support the body to allow a deeper expression of a yoga pose’s alignment. Yoga blocks are most often used as an extension of one’s hands, but are also used to support the back, head and hips, and to deepen awareness of alignment. A yoga block is most helpful for beginning students and those experiencing injury or other physical limitations, but more advanced practitioners can utilize props to safely learn new challenging poses. When purchasing a yoga block you will need to consider size, material, cost and number. B.K.S Iyengar’s stated ideal size for a yoga block is 9 x 4.5 x 3 inches, but you will find blocks that are both larger and smaller than this. Choosing a larger or smaller block will depend on the size of your hands and the level of your flexibility. If you have small hands and are fairly bendy you might want to consider a smaller sized block. Conversely, if you have larger hands and less flexibility think about choosing a larger block. Originally yoga blocks were made of wood, but now blocks also come in both foam and cork.

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Yoga bolster:

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A yoga bolster is a yoga accessory used to support the body while doing poses, intensify practice sessions or facilitate stretching. It is usually made of cotton and looks like a cushion with a removable cover. Yoga bolsters take strain off the body when easing from one pose to another. Yoga practitioners use different types of bolsters for different purposes. The most common types of yoga bolsters are rectangular and cylindrical bolsters. Rectangular bolsters are used in restorative yoga because their stable form allows for a deeper forward bend and a gentler chest opening. By contrast, cylindrical bolsters provide more support for forward bends and allow the chest to open deeper.

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Yoga space:

For many with families, small children, and tight spaces, developing a home practice—which can be a great option to counter-act the expense of yoga in studio/class can be challenging, but not impossible. All that you need to practice yoga is a space the size of a yoga mat, even if that’s the only floor space available. Meditation, of course, only requires a seated position. Wherever you allocate your “yoga space,” do something to make it feel sacred, even just lighting a candle or erecting a temporary altar. If you have kids and/or other “distractions” that make it challenging to practice, remember that peace has more to do with our inner, rather than external, environment. Use “distractions” as opportunities to meditate without reacting and to practice breath awareness.

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Three basic actions for yoga:

1. Going back to the breath. Mindful breathing is what elevates yoga above mere exercise. Breath is the link between mind and body, conscious and unconscious, personal and universal. Deep yogic breathing triggers the relaxation response, helping to prevent injuries, reduce stress and allow healing. And while the mind itself is a slippery thing, the breath gives us a tool for self-observation. Continually refining breath awareness will help you move past obstacles and experience more epiphanies (aha! moments).

2. Moving from the center. The safest way to practice most asanas is by initiating, assessing and adjusting from the spine (the body’s axis) to the extremities. When the spine is misaligned, an asana might feel awkward or lifeless—or even lead to injury. It’s essential to stretch and strengthen the muscles around the spine, and to modify poses (by bending the knees in Uttanasana, for example) as needed to keep the spine both long and strong. Doing this not only protects your back, but also frees physical movement and energetic flow.

3. Remembering the details. Our myriad parts and systems are connected on gross (seen) and subtle (unseen) levels: muscle and bone, fascia and fluids, nerve signals and hormones. After you’ve established the breath and aligned your spine, lightly extend your awareness throughout the body. In a standing asana, the feet influence the entire pose. The sitting bones and pelvis are the foundation of seated poses. The shoulders are key to relieving neck tension, freeing the breath and energizing the heart center. The toes, the jaw, the tongue, the scalp and the skin around the eyes are just a few of the places where hardness or stress can hide. Expanding your awareness will reveal pockets of “amnesia” and reinvigorate each asana, like shining a flashlight into the darkest corners of your being.

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Intelligently choose your asana practice:

Hatha yoga is a great way to check in with the body and bring balance to the gunas. Wisely choosing asanas that address your mental, emotional and physical states are an important part of this practice. The gunas come and go in different proportions throughout the courses of one’s day, week and even lifetime. If you’re heading to a yoga class because you feel imbalanced in some way, check-in to discover the cause of your imbalance. For example, if you’re feeling tired and physically unmotivated because of excessive thoughts or emotional stressors, an energetic and rajasic asana practice that challenges the body to move (rather than the mind) might bring about balance. However, if these rapidly moving thoughts are creating a lot of stress and anxiety, asanas that are too rajasic may be overly stimulating. In this case, a slower, tamasic asana practice (think: gentle or yin yoga) intended to ground and encourage the experience of support is an ideal way to bring about balance. When you’re feeling out-of-sorts, consult your intuition, consider your particular constitution, and honor the circumstances in the present-day circumstances in which you find yourself.

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If you are considering practicing Yoga:

•Do not use yoga to replace conventional medical care or to postpone seeing a health care provider about pain or any other medical condition.

•If you have a medical condition, talk to your health care provider before starting yoga.

•Ask a trusted source (such as your health care provider or a nearby hospital) to recommend a yoga practitioner. Find out about the training and experience of any practitioner you are considering.

•Everyone’s body is different, and yoga postures should be modified based on individual abilities. Carefully selecting an instructor who is experienced with and attentive to your needs is an important step toward helping you practice yoga safely. Ask about the physical demands of the type of yoga in which you are interested and inform your yoga instructor about any medical issues you have.

•Carefully think about the type of yoga you are interested in. For example, hot yoga (such as Bikram yoga) may involve standing and moving in humid environments with temperatures as high as 105°F. Because such settings may be physically stressful, people who practice hot yoga should take certain precautions. These include drinking water before, during, and after a hot yoga practice and wearing suitable clothing. People with conditions that may be affected by excessive heat, such as heart disease, lung disease, and a prior history of heatstroke may want to avoid this form of yoga. Women who are pregnant may want to check with their health care providers before starting hot yoga.

•Tell all your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

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Yoga class:

Classes can vary in duration from 45 minutes to 1 hour and 30 minutes. A longer class will give you more time for learning the breathing and relaxation and will give the teacher time to work with your individual ability. It’s worth speaking to a teacher about their approach before you sign up for a class. Yoga classes usually have 10 to 20 people, allowing for individual attention. Suggestions for getting the most out of your yoga class include:

•Wear comfortable clothes and take a blanket or mat, since many poses are performed sitting or lying down.

•Allow at least three or four hours since your last meal.

•Always tell your yoga teacher if you have a specific complaint, so they can advise against any asanas that may aggravate your problem.

•Always tell your yoga teacher if you are pregnant, have had a recent injury, illness, surgery, high blood pressure, heart problems or osteoporosis.

•Don’t talk during the class because it will disturb your own quiet focus and that of others in the class.

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Open Class:

An Open Class is a traditional, slow paced, meditative class that helps encourage proper breathing, flexibility, strength and vitality in the body while calming the mind. Because Yoga is a spiritual system with a physical component, this non-competitive approach helps the practitioner gain much more than just a healthy body. A typical open level class includes pranayama (breathing exercises), warm-ups including Sun Salutations (Surya Namaskar), 12 basic asanas (postures) and deep relaxation. The focus is on mastering the basic asanas from which variations are then added to further deepen the practice. The asanas follow an exact order that allows for the systematic movement of every major part of the body in a balanced way that enhances prana or life force energy, keeping the mind quiet and without the need to think beyond each individual pose. Additional variations may also be taught.

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Mobile App for learning Yoga:

The Isha Foundation’s ‘Yoga Tools from Sadhguru’ app offers seven yoga practice video demonstrations of 5 minute each as part of the first International Day of Yoga celebrations.  But the organisation’s founder Sadhguru Jaggi Vasudev clarifies, “This is not serious Yoga, this is called as UpaYoga or Pre Yoga. It’s a stepping stone for Yoga. We want people to have a taste of Yoga and experience and well-being that it offers. From that they can graduate to higher levels of yoga later on.”

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Prerequisites for Yoga:

1. Below 12 years of age Yoga postures should not be practiced for long duration and asanas are to be maintained for very short duration.

2. Every day you should practice Yoga for at least 30 to 45 minutes to get maximum results.

3. The best suited time to practice is early morning hours, but it can be practiced in the afternoon after following food restrictions.

4. Food restrictions – stomach should be empty while practicing, that is you should consume solid food 3.5 hours before practicing and liquid 1 hour before.

5. Place should be spacious, clean, airy, bright and away from disturbances.

6. Yoga should not be practiced on bare floor but keep mat or carpet below.

7. Clothes should be comfortable, loose, clean. Undergarments are necessary.

8. Yoga prefers vegetarian diet. But avoid spicy and hot diet as much as possible.

9. Women can practice only some asanas during pregnancy and menstruation.

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Yoga and food:

Yoga food is vegetarian. It is an eating philosophy based on a wholesome vegetarian diet. Its principles of healthy eating use vegetarian ingredients in combination with spices and herbs that have therapeutic value and delicious flavors. Why vegetarian? – Yoga food is based on the idea that foods must be consumed in their most natural forms in order to realize their true benefits. The yogic belief is that several health disorders can be traced to faulty nutrition, poor diet and difficulty in digestion. In order to stay healthy and happy food should be digested very easily! A vegetarian yoga diet ensures that all faculties of digestion work smoothly; absorption, assimilation, and elimination. The diet also contains high amounts of fiber and antioxidants. Yoga food helps to maintain a strong and healthy body, a stress-free mind, and a positive spirituality in our complex lifestyles. The benefits of a well-balanced vegetarian diet can be powerful.

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Yoga Food is classified into 3 categories Sattvic, Rajasic, and Tamasic Foods:

SATVIC FOOD RAJASIC FOOD TAMASIC FOOD
Sattvic foods are those which purify the body and calm the mind They stimulate the body and mind into action. In excess, these foods can cause hyperactivity, restlessness, anger, irritability, and sleeplessness Tamasic food are those which dull the mind and bring about inertia, confusion and disorientation
Cooked food that is consumed within 3-4 hours can be considered sattvic Overly tasty foods are Rajasic Stale or reheated food, oily or heavy food and food containing artificial preservatives fall under this category
Examples – Fresh fruits, green leafy vegetables, nuts, grains, fresh milk , certain spices Examples – Spicy food, onion, garlic, tea, coffee, fried food Example – Non vegetarian diet, stale food, excessive intake of fats, oil, sugary food

Sattvic Foods are foods that should be eaten the most and that are very easily digestible. These foods nourish the body, purify the mind and heal the imbalance in the body by generating good health, energy, vitality, vigor, mental alertness, peace and strength. Rajasic Foods are foods that should be eaten moderately or occasionally and are foods that are not as easily digestible like Sattvic foods. Although, these foods create restlessness and provide extra-stimulation, it is sometimes required when the body needs higher amounts of energy or during the fall and winter seasons. Tamasic Foods are foods that should be eaten the least and are foods that are difficult to digest. These foods require a lot more energy to digest and are known to be the least beneficial to the mind and the body. Tamasic foods can enhance dullness, lethargy, depression the body feel heavy, generating the least amount of energy. When eaten too often or in excess they could destroy the body’s resistance to disease.

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Why are you supposed to refrain from eating two to three hours before Yoga class?

In yoga practice we twist from side to side, turn upside down, and bend forward and backward. If you have not fully digested your last meal, it will make itself known to you in ways that are not comfortable. If you are a person with a fast-acting digestive system and are afraid you might get hungry or feel weak during yoga class, experiment with a light snack such as yogurt, a few nuts, or juice about 30 minutes to an hour before class.

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Who cannot do yoga?

Yoga can be safe for everyone, but depending on the medical condition, certain poses may need to be modified or avoided. A couple of examples of patients who may need to avoid certain yoga poses include:

•Patients who have been diagnosed with advanced spinal stenosis should avoid extreme extension of the spine such as back bends in yoga.

•Patients with advanced cervical spine disease should avoid doing headstands and shoulder stands in yoga.

Most of the precautions surrounding the yoga poses can be determined by understanding the specific medical condition, using common sense, and finding a good yoga teacher to assist.

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Should you practice Yoga when you’re Sick?

When illness has you feeling down, you may wonder, “Should I still practice yoga?” Though we cannot speak on behalf of doctors, most yoga teachers suggest sticking with your practice during times of illness—though your “practice” may differ from when you’re feeling physically well. Asana, especially in gentle forms, is inherently healing and balancing to the body. Same goes for meditation and certain purification and cleansing practices. The important thing to remember if practicing while sick is to be gentle and listen to your body (sometimes the most yogic thing you can do is rest!).

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Yoga precautions:

Yoga is generally considered safe for most healthy people when practiced under the guidance of a trained instructor. But there are some situations in which yoga might pose a risk.  See your health care provider before you begin yoga if you have any of the following conditions or situations:

•A herniated disk

•A risk of blood clots

•Deconditioned state

•Eye conditions, including glaucoma

•Pregnancy

•Severe balance problems

•Severe osteoporosis

•Uncontrolled blood pressure

You may be able to practice yoga in these situations if you take certain precautions, such as avoiding certain poses or stretches. If you develop symptoms or concerns, see your doctor to make sure you’re getting benefit and not harm from yoga.

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Yoga Safety Tips:

•Work with a qualified yoga instructor. Ask about his or her experience and credentials. If you choose to use a yoga DVD at home, look for one that comes highly recommended by your physician or other reliable sources.

•Warm up thoroughly before a yoga session. Cold muscles, tendons and ligaments are vulnerable to injury. Make sure you cool down as well to relax your muscles and restore your resting heart rate and breathing rhythm.

•Wear appropriate clothing that allows for proper movement. Stay hydrated by drinking plenty of fluids.

•Select the class level that is appropriate for you. Start by taking a single beginner or introductory class before signing up for a complete session or class series.

•If you are unsure of a pose or movement, ask questions. Your instructor should be able to suggest modified positions for older adults.

•Know your limits. Do not try positions beyond your experience or comfort level. Beginners should start slowly and learn the basics first, focusing on gentle stretching and breathing rather than trying to accomplish difficult poses.

•Learn what type of yoga you are performing. There are hundreds of different forms of yoga, some more strenuous than others. It is important to learn which type of yoga will best suit your needs.

•Listen to your body. If you experience pain or exhaustion while participating in yoga, stop or take a break. If pain persists, speak with your physician.

•Discuss any known illness or injury with your yoga instructor prior to the class so that he or she can recommend pose modifications.

•If you have an underlying joint or spinal injury or arthritis, gentle stretching helps avoid stiffness. Remember, however, that just as in all other activity, flare-ups of pain or injury may occur with yoga if tissues are stretched or stressed too quickly and beyond their physiologic level.

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Advantages of yoga:

Yoga has many advantages over other methods of maintaining health, such as gymnastics, athletics, aerobics, games, and various other forms of exercise. It does not need any costly equipment and materials, or playgrounds, swimming pool, gyms, etc. Yoga can be practiced throughout the year. It can also be practiced inside the house or in the open, singly or in groups. The only requirement is a thick carpet spread on the floor and covered with a clean sheet of cloth. Yoga should only be practiced on empty stomach. You can do it at any time during the day. It will benefit you irrespective of whether you are young or old, lean or heavily built, highly educated or unlettered, rich or poor, from higher or lower middle class, busy, over busy, or retired or worker in the factory or in the field. To reap the intangible benefits of yoga, it helps to be humble and to realize that yoga is meant to be practiced, not perfected. It’s a non-competitive activity. Yoga has something very valuable, and useful to offer to everyone. It is often described as the best form of health insurance for all from the age of 7 to 77 or more. Two main advantages of Yoga are prevention of disorders and ailments, and maintenance of health and fitness in daily life. Other advantage include flexible muscles, supple joints, relaxed and tension–free mind and efficiently working vital organs such as the heart, lungs, endocrine glands, liver, pancreas and good balance between various functions, such as neuromuscular coordination, etc.

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Disadvantages of Yoga:

If you only have 20 minutes a day to spend on your body and your foremost goal is to burn lots of calories, yoga will disappoint you. Although yoga is a sound adjunct to any weight–loss program and has even been shown to promote gradual weight loss, it is not primarily a fat–burning enterprise. Another potential pitfall is finding a qualified teacher. Before enrolling in a class, ask what type of training the instructor had. A good yoga instructor asks each student if she has strains or injuries, and will tailor the instructions to any injured students. Currently, there is no national certification program for yoga instructors. Voluntary certification is available from various groups, but some organizations award teaching certificates to people who have completed only a weekend course. The Yoga Alliance – a voluntary national coalition of yoga organizations and individual yoga teachers – is seeking to establish voluntary national standards for yoga teachers, but not all yoga instructors agree with those standards or support the alliance’s philosophy. Even for the most open–minded beginner, yoga is not easy to learn. Although you don’t need to be flexible or in shape to do yoga, the practice is physically, emotionally and mentally challenging. The Yogasana process is far more complex than it looks. It takes a lot of time to reach the highest level of perfection. When you don’t start Yogasana as a basic point and ignore your physical and emotional ability to do it, this can end up into serious injury.  So we can say that, although yoga has several advantages, it has also proved to be harmful if not worked out properly and according to the need of an individual.  One of yoga’s draws is its potential to help you better listen to yourself, connecting your mind with your body and helping you to meditate and de-stress. However, some modern variations of yoga now incorporate elements like music and similar Western-style gimmicks. This can detract from yoga’s meditative purposes and reduce some of its advantages.

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Origin of yoga:

Yoga began in India as early as 3000 B.C. according to archaeological evidence. It emerged in the later hymns of the ancient Hindu texts (Upanishads or Vedanta) (600–500 B.C.). It is mentioned in the classic Indian epic Mahabharata (300 B.C.) and discussed in the most famous part, the Bhagavad Gita. Yoga was systemized by Patanjali in the Yoga Sutras (400 CE). Patanjali defined the purpose of yoga as knowledge of the true “Self” and outlined eight steps for direct experience of “Self.”  Hatha yoga texts emerged around 11th century CE, and in its origins was related to Tantrism. In the late 1800s and early 1900s, yoga masters began to travel to the West, attracting attention and followers. This began at the 1893 Parliament of Religions in Chicago, when Swami Vivekananda wowed the attendees with his lectures on yoga and the universality of the world’s religions. In the 1920s and 30s, Hatha Yoga was strongly promoted in India with the work of T. Krishnamacharya, Swami Sivananda and other yogis practicing Hatha Yoga. Krishnamacharya opened the first Hatha Yoga school in Mysore in 1924 and in 1936 Sivananda founded the Divine Life Society on the banks of the holy Ganges River. Krishnamacharya produced three students that would continue his legacy and increase the popularity of Hatha Yoga: B.K.S. Iyengar, T.K.V. Desikachar and Pattabhi Jois. Sivananda was a prolific author, writing over 200 books on yoga, and established nine ashrams and numerous yoga centers located around the world. The importation of yoga to the West still continued at a trickle until Indra Devi opened her yoga studio in Hollywood in 1947. Since then, many more western and Indian teachers have become pioneers, popularizing hatha yoga and gaining millions of followers. Hatha Yoga now has many different schools or styles, all emphasizing the many different aspects of the practice. In the 1980s, yoga became popular as a system of physical exercise across the Western world. Yoga in Indian traditions, however, is more than physical exercise, it has a meditative and spiritual core.

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Yoga and religion:

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Philosophical schools of Hinduism:

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Yoga is a classical philosophy: Yoga is one of six schools of Hindu philosophy. These are Nyaya, Visheshika, Mimasa, Sankhya, Yoga, and Vedanta. Yoga is one of the systems of Hindu philosophy which has been discussed in various Indian scriptures such as the Bhagavad Gita, the Ahirbudhyna Samhita, the Upanishads and the yoga sutra-s of Sage Patanjali.  Yoga is a Hindu physical, mental, and spiritual practice or discipline. Yoga is a philosophy of Hinduism that requires mental, physical and spiritual connection in order to achieve enlightenment. Lord Shiva was the first yogi as per the authentic Vedic texts in which Yoga was first taught. According to legend, Lord Shiva is credited with propounding hatha yoga. It is said that on a lonely island, assuming nobody else would hear him, he gave the knowledge of hatha yoga to the Goddess Parvati, but a fish heard the entire discourse, remaining still throughout. The fish (Matsya) later became a siddha and came to be known as Matsyendranath. Matsyendranath taught hatha yoga to his disciple Gorakshanath. Patañjali, a siddha of the 4th century BCE, in his treatise on Yoga, The Yoga Sutras, describes asana and pranayama as two limbs of the practice of Ashtanga Yoga, although many assert that Patanjali’s sutras do not support the practice of asana as physical exercise. There is a broad variety of schools, practices and goals in Hinduism, Buddhism (including Vajrayana and Tibetan Buddhism) and Jainism.

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Hindu practitioners of yoga are proud of their religious traditions, while non-Hindu practitioners claim that yoga may be practiced sincerely by those who have not accepted the Hindu religion. While the yoga tradition remains rooted in India, the fact that some modern yogis like Swami Vivekananda and Paramahansa Yogananda came to the West suggests that they saw hope the yoga tradition could also flourish there. Critics of yoga as practiced in the West charge that it is sometimes watered down, corrupted, or cut off from its spiritual roots (e.g. the popular view that yoga is primarily physical exercises). If yoga is one of India’s great gifts to the world, the widespread acceptance of that gift – with the concomitant diversity – is sometimes incomprehensible to traditional Hindu practitioners of yoga. Yet the sheer number of people practicing yoga outside India suggests the need to define yoga both by its historical roots and its modern adaptations.

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Malaysia’s top Islamic body in 2008 passed a fatwa, prohibiting Muslims from practicing yoga, saying it had elements of Hinduism and that its practice was blasphemy, therefore haraam.  Some Muslims in Malaysia who had been practicing yoga for years, criticized the decision as “insulting.”  Sisters in Islam, a women’s rights group in Malaysia, also expressed disappointment and said yoga was just a form of exercise. This fatwa is legally enforceable.  However, Malaysia’s prime minister clarified that yoga as physical exercise is permissible, but the chanting of religious mantras is prohibited.  In 2009, the Council of Ulemas, an Islamic body in Indonesia, passed a fatwa banning yoga on the grounds that it contains Hindu elements. These fatwas have, in turn, been criticized by Darul Uloom Deoband, a Deobandi Islamic seminary in India. Similar fatwas banning yoga, for its link to Hinduism, were issued by the Grand Mufti Ali Gomaa in Egypt in 2004, and by Islamic clerics in Singapore earlier. In Iran, as of May 2014, according to its Yoga Association, there were approximately 200 yoga centres in the country, a quarter of them in the capital Tehran, where groups can often be seen practising in parks. This has been met by opposition among conservatives.  In May 2009, Turkey’s head of the Directorate of Religious Affairs, Ali Bardakoğlu, discounted personal development techniques such as reiki and yoga as commercial ventures that could lead to extremism. His comments were made in the context of reiki and yoga possibly being a form of proselytization at the expense of Islam.

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Is Yoga a religion?

No.

Because yoga has its roots in the Hindu culture of India, there is a popular misconception that yoga is a religion. Just as the practice of the Japanese martial arts of karate and aikido does not require becoming a Buddhist, the practice of yoga does not require you adopt Hinduism. Rather yoga is nonsectarian, promoting health and harmonious living. Yoga offers a simple, accessible and inclusive means to promote physical and spiritual health. And yoga does not discriminate; to varying degrees, all people can practise, regardless of their relative strength, age or ability.

Here are a few of the things that are usually part of religions, but which are missing with Yoga:

Yoga has no deity to worship.

Yoga has no worship services to attend.

Yoga has no rituals to perform.

Yoga has no sacred icons.

Yoga has no creed or formal statement of religious belief.

Yoga has no requirement for a confession of faith.

Yoga has no ordained clergy or priests to lead religious services.

Yoga has no institutional structure, leader or group of overseers.

Yoga has no membership procedure.

Yoga has no congregation of members or followers.

Yoga has no system of temples or churches.

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Samkhya, yoga, dualism and atheism:

Many traditions in India began to adopt systematic methodology by about first century CE. Of these, Samkhya was probably one of the oldest philosophies to begin taking a systematic form.  Patanjali systematized Yoga, building them on the foundational metaphysics of Samkhya. In the early works, the Yoga principles appear together with the Samkhya ideas. Vyasa’s commentary on the Yoga Sutras, also called the Samkhyapravacanabhasya (Commentary on the Exposition of the Sankhya Philosophy), describes the relation between the two systems. The two schools have some differences as well. Yoga accepted the conception of “personal god”, while Samkhya developed as a rationalist, non-theistic/atheistic system of Hindu philosophy. Sometimes Patanjali’s system is referred to as Seshvara Samkhya in contradistinction to Kapila’s Nirivara Samkhya. The parallels between Yoga and Samkhya were so close that Max Müller says that “the two philosophies were in popular parlance distinguished from each other as Samkhya with and Samkhya without a Lord….”

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Samkhya is known for its theory of gunas (qualities, innate tendencies).  Guna, it states, are of three types: Sattva being good, compassionate, illuminating, positive, and constructive; Rajas guna is one of activity, chaotic, passion, impulsive, potentially good or bad; and Tamas being the quality of darkness, ignorance, destructive, lethargic, negative. Everything, all life forms and human beings, state Samkhya scholars, have these three gunas, but in different proportions. The interplay of these gunas defines the character of someone or something, of nature and determines the progress of life. The Samkhya theory of gunas was widely discussed, developed and refined by various schools of Indian philosophies including Buddhism. Samkhya’s philosophical treatises also influenced the development of various theories of Hindu ethics.

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While Western philosophical traditions, as exemplified by Descartes, equate mind with the conscious self and theorize on consciousness on the basis of mind/body dualism; Samkhya provides an alternate viewpoint, intimately related to substance dualism, by drawing a metaphysical line between consciousness and matter — where matter includes both body and mind. The Samkhya system espouses dualism between consciousness and matter by postulating two irreducible, innate and independent realities: Purusha and Prakriti. While the Prakriti is a single entity, the Samkhya admits a plurality of the Puruṣas in this world. Unintelligent, unmanifest, uncaused, ever-active, imperceptible and eternal Prakriti is alone the final source of the world of objects which is implicitly and potentially contained in its bosom. The Puruṣa is considered as the conscious principle, a passive enjoyer (bhokta) and the Prakriti is the enjoyed (bhogya). Samkhya believes that the Puruṣa cannot be regarded as the source of inanimate world, because an intelligent principle cannot transform itself into the unconscious world. It is a pluralistic spiritualism, atheistic realism and uncompromising dualism.

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Samkhya accepts the notion of higher selves or perfected beings but rejects the notion of God. Classical Samkhya argues against the existence of God on metaphysical grounds. Samkhya theorists argue that an unchanging God cannot be the source of an ever changing world and that God was only a necessary metaphysical assumption demanded by circumstances. The Sutras of Samkhya have no explicit role for a separate God distinct from the Puruṣa. Such a distinct God is inconceivable and self-contradictory and some commentaries speak plainly on this subject.

The following arguments were given by the Samkhya philosophers against the idea of an eternal, self-caused, creator God:

1. If the existence of karma is assumed, the proposition of God as a moral governor of the universe is unnecessary. For, if God enforces the consequences of actions then he can do so without karma. If however, he is assumed to be within the law of karma, then karma itself would be the giver of consequences and there would be no need of a God.

2. Even if karma is denied, God still cannot be the enforcer of consequences. Because the motives of an enforcer God would be either egoistic or altruistic. Now, God’s motives cannot be assumed to be altruistic because an altruistic God would not create a world so full of suffering. If his motives are assumed to be egoistic, then God must be thought to have desire, as agency or authority cannot be established in the absence of desire. However, assuming that God has desire would contradict God’s eternal freedom which necessitates no compulsion in actions. Moreover, desire, according to Samkhya, is an attribute of prakriti and cannot be thought to grow in God. The testimony of the Vedas, according to Samkhya, also confirms this notion.

3. Despite arguments to the contrary, if God is still assumed to contain unfulfilled desires, this would cause him to suffer pain and other similar human experiences. Such a worldly God would be no better than Samkhya’s notion of higher self.

4. Furthermore, there is no proof of the existence of God. He is not the object of perception, there exists no general proposition that can prove him by inference and the testimony of the Vedas speak of prakriti as the origin of the world, not God.

Therefore, Samkhya maintained that the various cosmological, ontological and teleological arguments could not prove God.

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Yoga is closely related to Samkhya in its philosophical foundations. The Yoga school derives its ontology and epistemology from Samkhya and adds to it the concept of Isvara (God). However, scholarly opinion on the actual relationship between Yoga and Samkhya is divided. Yoga is a philosophical school in Hinduism, and sometimes referred to as Rāja yoga. Yoga, in this context, is one of the six āstika schools of Hinduism (those which accept the Vedas as source of knowledge).  The Yoga Sutras of Patanjali is considered as a central text of the Yoga school of Hindu philosophy.  As a school of philosophy, Yoga is a way of life, and incorporates its own epistemology, metaphysics, ethical practices, systematic exercises and self-development techniques for body, mind and spirit. Its epistemology (pramanas) is same as the Samkhya school. Both accept three reliable means to knowledge – perception (pratyākṣa, direct sensory observations), inference (anumāna) and testimony of trustworthy experts (sabda, agama). Both these orthodox schools are also strongly dualistic.

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Spirituality and yoga:

Spirituality is a sense of connectedness with something greater than oneself. Spirituality is inclusive. We all participate in the spiritual at all times, whether we know it or not. There’s no place to go to be separated from the spiritual. The most important thing in defining the spirit is the recognition that spirit is an essential need of human nature.  Many people begin to cultivate a greater sense of connection with each other, with the physical world and with the ‘self’ simply by practicing the physical postures, control of the breath and meditation. People who choose to can also study the moral precepts of yoga. These guidelines for healthy living are known as the yamas and the niyamas. The yamas are universal guidelines for ways of interacting with others and include nonviolence, truthfulness, no stealing, moderation and no hoarding. The niyamas are personal observances and include purity, contentment, zeal, self-study and devotion to a higher power. Together, the yamas and the niyamas are moral and behavioral observances that serve as a catalyst to self-acceptance, healthy relationships and spiritual growth.

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Physiology of yoga:

Yoga physiology are the descriptions of the human body, its layers, and the energy channels running through it used in various yoga systems.

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According to the Doctrine of the Three bodies in the Vedanta and Yoga, the human being is composed of three Sariras or “bodies”. They are often equated with the five koshas (sheets), described in the Taittiriya Upanishad describes five koshas or sheets which cover the Atman or “Self”.

They are:

1. Sthula sarira, the Gross body, composed of the Annamaya Kosha

2. Suksma sarira, the Subtle body, composed of:

A. Pranamaya Kosha (Vital breath or Energy),

B. Manomaya Kosha (Mind),

C. Vijnanamaya Kosha (Intellect)

3. Karana sarira, the Causal body, composed of the Anandamaya Kosha (Bliss)

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Chakras are energy points or knots in the subtle body. They are located at the physical counterparts of the major plexuses of arteries, veins and nerves. Chakras are part of the subtle body, not the physical body, and as such are the meeting points of the subtle (non-physical) energy channels, called nadiis. Nadiis are channels in the subtle body through which the life force (prana), or vital energy moves. Various scriptural texts and teachings present a different number of chakras. There are many chakras in the subtle human body according to the tantric texts, but there are 7 chakras that are considered to be the most important ones. Their name derives from the Sanskrit word for “wheel” or “turning”, but in the yogic context a better translation of the word is ‘vortex or whirlpool’.

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Nadi:

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Nāḍi (tube, pipe”) are the channels through which, in traditional Indian medicine and spiritual science, the energies of the subtle body are said to flow. They connect at special points of intensity called chakras. In normal biological reference, a nadi can be translated into “nerve” in English. However, in yogic, and specifically in Kundalini yoga reference, a nadi can be thought of as a channel (not an anatomical structure). In regard to Kundalini yoga, there are three of these nadis: Ida, pingala, and sushumna. Ida (spoken “iRda”) lies to the left of the spine, whereas pingala is to the right side of the spine, mirroring the ida. Sushumna runs along the spinal cord in the center, through the seven chakras – Mooladhaar at the base, and Sahasrar at the top (or crown) of the head. It is at the base of this sushumna where the Kundalini lies coiled in three and a half coils, in a dormant or sleeping state.

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Chakras:

 

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The word chakra means “spinning wheel.” According to the yogic view, chakras are a convergence of energy, thoughts, feelings, and the physical body. They determine how we experience reality from our emotional reactions, our desires or aversions, our level of confidence or fear, even the manifestation of physical symptoms.  When energy becomes blocked in a chakra, it is said to trigger physical, mental, or emotional imbalances that manifest in symptoms such as anxiety, lethargy, or poor digestion. The theory is to use asanas to free energy and stimulate an imbalanced chakra.

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Seven chakras:

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1. Sahasrara: the “thousand petaled” or “crown chakra” represents the state of pure consciousness. This chakra is located at the crown of the head and signified by the color white or violet. Sahasrara involves matters of inner wisdom and death of the body.

2. Ajna: the “command” or “third-eye chakra” represents a meeting point between two important energetic streams in the body. Ajna corresponds to the colors violet, indigo or deep blue, though it is traditionally described as white. The chakra is connected to the pituitary gland, growth and development.

3. Vishuddha: the “especially pure” or “throat chakra” is symbolized by the color red or blue. This chakra represents the home of speech and hearing, and the endocrine glands that control metabolism.

4. Anahata: the “unstruck” or “heart chakra” is related to the colors green or pink. Key issues involving Anahata involve complex emotions, compassion, tenderness, unconditional love, equilibrium, rejection and well-being.

5. Manipura: the “jewel city” or “navel chakra” is symbolized by the color yellow. This chakra is associated with the digestive system, along with personal power, fear, anxiety, opinion formation and introversion.

6. Svadhishthana: “one’s own base” or “pelvic chakra” represents the home of the reproductive organs, the genitourinary system and the adrenals.

7. Muladhara: the “root support” or “root chakra” is located at the base of the spine in the coccygeal region. It is said to hold our instinctual urges around food, sleep, sex, and survival. It is also the realm of our avoidance and fears.

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Each chakra is associated with a certain part of the body and a certain organ which it provides with the energy it needs to function. Additionally, just as every organ in the human body has its equivalent on the mental and spiritual level, so too every chakra corresponds to a specific aspect of human behavior and development. Our circular spirals of energy differ in size and activity from person to person. They vibrate at different levels relative to the awareness of the individual and their ability to integrate the characteristics of each into their life.  The lower chakras are associated with fundamental emotions and needs, for the energy here vibrates at a lower frequency and is therefore denser in nature. The finer energies of the upper chakras corresponds to our higher mental and spiritual aspirations and faculties.  The openness and flow of energy through our chakras determines our state of health and balance. Knowledge of our more subtle energy system empowers us to maintain balance and harmony on the physical, mental and spiritual level. All meditation and yoga systems seek to balance out the energy of the chakras by purifying the lower energies and guiding them upwards.  Through the use of grounding, creating “internal space,” and living consciously with an awareness of how we acquire and spend our energy we become capable of balancing our life force with our mental, physical and spiritual selves. The yogic chakra system consists of seven chakras which are normally depicted as a sort of ‘spinal column’ with three channels called nadis (ida, pingala and sushumna) which interweave, the crossing-points being the sites of the chakras. These seven chakras, or energy centers, in the body become blocked by longheld tension and low self-esteem. But practicing poses that correspond to each chakra can release these blocks and clear the path to higher consciousness. The postures precisely address the tension, holding, and blockage of energy in any particular joint or organ. As this tension is released, energy flows more readily throughout the body and allows patients to experience a sense of increased well-being and strength as well as a balance of mind, body and spirit. More than just stretching and toning the physical body, the yoga poses open the nadis (energy channels) and chakras (psychic centers) of the body. Yoga poses also purify and help heal the body, as well as control, calm and focus the mind. The different categories of postures produce different energetic, mental, emotional and physical effects.

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Chakras are said to determine how we experience reality from our emotional reactions, our desires or aversions, our level of confidence or fear, even the manifestation of physical symptoms.

The figure above shows that chakras are having effects on endocrine glands.

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Physiology of Pranayama:

‘Prana’ refers to the universal life force and ‘ayama’ means to regulate or lengthen. Prana is the vital energy needed by our physical and subtle layers, without which the body would perish. It is what keeps us alive. Pranayama is the control of prana through the breath. These techniques rely on breathing through the nostrils. Prana flows through thousands of subtle energy channels called ‘nadis’ and energy centers called ‘chakras’. The quantity and quality of prana and the way it flows through the nadis and chakras determines one’s state of mind. If the Prana level is high and its flow is continuous, smooth and steady, the mind remains calm, positive and enthusiastic. However, due to lack of knowledge and attention to one’s breath, the nadis and chakras in the average person may be partially or fully blocked leading to jerky and broken flow. As a result one experiences increased worries, fear, uncertainty, tensions, conflict and other negative qualities. The ancient sages of India realized these breathing techniques. Some common pranayamas include Bhastrika, Kapalabhati, and Nadi shodan pranayama. Regular practice increases and enhances the quantity and quality of prana, clears blocked nadis and chakras, and results in the practitioner feeling energetic, enthusiastic and positive. Practiced correctly under the right supervision prananyama brings harmony between the body, mind and spirit, making one physically, mentally and spiritually strong.

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Hatha Yoga and energy system:

It is similar to a diving board – preparing the body for purification, so that it may be ready to receive higher techniques of meditation. The word “Hatha” comes from “Ha” which means Sun, and “Tha” which means Moon. Hatha Yoga blends energizing and dynamic yoga postures (represented by the sun) with relaxing and meditative yoga postures (represented by the moon). By combining both types of postures, the body receives the maximum benefit. Our body is made up of a highly intricate energy system. To experience good health and wellness, the energy flow should be in balance. Too little energy (Tamas) can result in a dull and lethargic mind, and a heavy and inert body. Excess energy (Rajas) results in an angry and irritable mind, and a restless body. When the energy is in balance, health and vitality is experienced and this constitutes the goal of Hatha Yoga. This state of perfect balance of energy in the system is called Satva, and is expressed by a relaxed, alert mind, and a light and energetic body. Hatha Yoga offers a balanced and well-rounded sequence of Yoga Postures. For example, the Art of Living Yoga sequence of postures intertwines active and passive postures so that the energy in the body is guided to the perfect place of equilibrium. Here, the emphasis is on practicing asanas (postures) and pranayamas (breathing techniques) with strong (hatha also means ‘strong’) determination.

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Kundalini:

 

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Yoga asana vs. exercise:

It is very true that exercise and Asana are related to the muscular system of body. But in exercise, more emphasis is given on movement and stress of the muscles whereas, in Asana, it is given on steadiness of muscles. Yoga Maharshi Patanjali has defined Yoga Asana as, “Asana means a steady and comfortable state.” Patanjali, who is the founder of eight-fold Hatha/Ashtanga Yoga, has said that to perfect a posture, one should be able to hold it comfortably for 3 hours. In light of this definition, it can be noticed that exercise and Asana are two distinct concepts, i.e. they work in the exactly opposite directions to each other. In the state of Asana, stability and comfort of the body parts and muscles is to be achieved by practicing a specific movement, slowly with control. If the movements are fast, then it will be difficult to attain steadiness in later states of Asana. While practicing such movements, some muscles may get stressed. At this time, if you try to keep muscles relaxed, breathing and speaking to your body, then both the pressure and stress on the muscles will be relieved. Try to concentrate on your body movements. Muscles that take part in these movements will be pressed to the required extent only, and little to no stress or discomfort will be incurred. With the help of such movements, the expected results can be experienced, the Yoga practitioner can breathe deeply and freely, and the body will remember the position comfortably and positively. It is helpful to know the impact of these movements on other systems of the body as well. In exercise, if we increase the speed of movements, then muscles are under strain. The speed of blood circulation and blood pressure increases, and the heart has to perform extra work. Exactly opposite results are obtained due to Asana. Once you have undergone any particular state in an Asana, blood requirement is reduced as the body is relaxed, and stress on the heart is actually relieved. The same effect takes place on the respiratory system during exercise. Due to rapid movements, the lungs have to perform extra tasks. The muscles need an increase of oxygen, and breathing takes place rapidly. If the speed of the heartbeat increases, speed of breathing also increases. In Asana, the body’s requirement of oxygen and thus, the speed of respiration reduce so there is no overload on the respiratory system. The tortoise breathes once every 5 minutes; he requires little oxygen and is the longest living creature on earth. The second longest lifespan is that of the elephant, breathing once every 3 minutes. Reduction in the speed of respiration equals longevity. While performing exercise, muscle strength is increased and through Asana muscle stamina is increased. Asana enables the muscles to work for a longer period of time without strain. This increased tolerance to strain lies in the manner of how you practice both Asana and exercise. In some case, both heartbeat and speed of respiration may increase during Asana practice. Hence, provisions for breathing are also made while performing Asana. It is difficult to maintain the steadiness of muscles initially, but it is easy to practice the movements into the Asana steadily. In the study of yoga, all stages are important and easy to practice slowly with control. Yoga does not cause fatigue like other workout. Even at any age you can do yoga while other workouts cannot be done in elderly.

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Yoga and exercise are not the same. Yoga is different from exercise as it doesn’t involve speedy movements, but instead very slow and steady movements. Exercises are aimed at building your muscles and physical strength and endurance.  Exercises involve repetition of certain movements aimed at building a certain group of muscles, thereby increasing the muscle weight and improving strength of those body parts. It increases the blood supply to those parts. Most exercises increase your breath rate and heart rate. You consume more oxygen during exercises than when you are doing your daily routine activities. Yoga asanas on the other hand, work in a totally different fashion. The idea of asanas is not building muscles, but harmonizing the body, breath and mind, thereby contributing to the overall health of the individual. In the Patanjali Yoga Sutras, asana is described as “Sthiram Sukham Asanam”, which means that which gives steadiness, stability and pleasure is called Asana. From this definition, it is clear that unlike exercises, you cannot do asanas with strain or tension. There is no extra load on the respiratory and cardiac systems. It has to be done in a steady and calm manner and should induce peace and sense of well-being. The oxygen consumption during asanas is lesser than your daily regular activities. Asanas reduces your breath and heart rate. Yoga decreases your Basal Metabolic Rate while exercises increase it. When performing asanas, your body is learning to use much less resources and be more efficient. Yoga asana doesn’t burn your calories as much as exercises. Yoga practitioners will need less food consumption than those who do exercises. Exercises can build up toxins in the body, while Yoga asanas help in eliminating toxins. Asanas help in optimal secretions of the endocrinal glands, thereby balancing the emotions and improving relationships and social interactions. The effect of yoga goes beyond the body. Benefits of yoga include not only strength and steadiness of the body, but also physiological and mental health. Yoga prevents as well as alleviates health problems. Finally, one has to understand that Yoga asanas were developed as part of spiritual science. The goal of yoga is primarily spiritual. Health and other benefits are secondary, though today most practitioners take to yoga for its physical and mental benefits. Yoga improves awareness in all our activities. Asanas are a prerequisite for the higher practices of pranayama, meditation and samadhi. In yoga you work the entire body in harmony in every single pose. The aim is to create a balance of skin, muscles, and bone so that our energy, breath, and fluids can flow without obstruction. Of course, this may not be your immediate experience because certain body parts are stronger than others. Instead you may feel more effort or get tired in areas that are not as strong. That’s just part of the process of gaining equal strength and awareness throughout the entire body. Another thing that sets yoga apart: In some workout regimes, you can tell if you are not doing an exercise correctly because you don’t “feel” anything. In yoga if you don’t feel anything, it may mean that you are in complete balance and as a result, your physical sensations are harmonious. When you do feel one area more intensely than another, you may notice that your mind fixates on that spot. If this happens, it can serve as a wake-up call to bring the attention back to the breath and let go of the effort throughout the body. When you experience equanimity of body, the mind starts to come to stillness and experience equanimity as well. Yoga is a done in one place, as a stationary exercise, and the movements are not jerky or hurried. It is done with bare feet and there is no need for equipment of any kind. A floor mat and perhaps a folded towel to support the back for the exercises that are done while lying down are required. Yoga does not burn body fat as fast as aerobic exercises do. It also lays greater emphasis on the release of contained energy and the mind-body-spirit connection.

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Yoga Benefits versus Exercise Benefits:

Yoga Benefits:

•Parasympathetic Nervous System dominates

•Subcortical regions of brain dominate

•Slow dynamic and static movements

•Normalization of muscle tone

•Low risk of injuring muscles and ligaments

•Low caloric consumption

•Effort is minimized, relaxed

•Energizing (breathing is natural or controlled)

•Balanced activity of opposing muscle groups

•Noncompetitive, process-oriented

•Awareness is internal (focus is on breath and the infinite)

•Limitless possibilities for growth in self-awareness

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Exercise Benefits:

•Sympathetic Nervous System dominates

•Cortical regions of brain dominate

•Rapid forceful movements

•Increased muscle tension

•Higher risk of injury

•Moderate to high caloric consumption

•Effort is maximized

•Fatiguing (breathing is taxed)

•Imbalance activity of opposing groups

•Competitive, goal-oriented

•Awareness is external (focus is on reaching the toes, reaching the finish line, etc.)

•Boredom factor

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Is Yoga Cardio?

The definition of Cardio:

The American College of Sports Medicine (ACSM) defines aerobic (cardio) exercise as “any activity that uses large muscle groups, can be maintained continuously, and is rhythmic in nature.” It is also defined as exercise that increases the need for oxygen and elevates the heart rate to a specific level, typically at least 60-70% of one’s max heart rate. Your maximum heart rate is about 220 minus your age. Traditional forms of cardio (think running, biking, swimming) use the largest muscle groups in the body in a rhythmic, continuous nature. This is what increases the heart rate to what is defined as an “aerobic” level and holds it there for several minutes at a time. Jogging, brisk walking, cycling, swimming and dancing are examples of aerobic exercise. Your heart rate increases to a minimum of 55 percent of maximum for low- to moderate-intensity training or as high as 90 percent of maximum for vigorous-intensity aerobics. The official position of the American College of Sports Medicine on cardiorespiratory training is that you should do bouts lasting 10 minutes or longer to accumulate at least 20 to 60 minutes total, three to five times per week.

The Benefits of Cardio:

Aerobic exercise strengthens your heart and lungs (which make up the cardiovascular system). During exercise, your muscles demand more oxygen-rich blood and give off more carbon dioxide and other waste products. As a result, your heart has to beat faster to keep up. When you follow a consistent aerobic exercise plan, your heart grows stronger so it can meet the muscles’ demands without as much effort. Everyone, regardless of their weight, age, or gender, can benefit from aerobic exercise. In addition, cardio burns more calories than any other type of exercise, making it the go-to type of exercise for weight loss. As we know, the more calories you burn, the more weight you’ll be able to lose. So if weight-loss is a goal of yours, calorie burning is key.

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It can be hard to make a blanket generalization about yoga when there are so many styles and disciplines under the yoga umbrella. Some are definitely not much of a workout. Others can be fast-paced and more intense.  But most types of yoga share the same poses—just done at different paces. Some of those poses use the “large muscle groups” of the body. Others don’t. Holding any one pose (even though this is strength-building isometric exercise) for more than a couple of seconds diminishes the rhythmic nature and therefore the cardio workout potential. Other types of yoga, such as faster-paced Ashtanga or “power” styles involve fewer holds/pauses and move practitioners quickly from one pose to the next. While these involve more “rhythmic” and “continuous” movements, it may or may not be enough to elevate your heart rate to an aerobic level—depending on the class itself and your own fitness level. Here’s a related example. Walking can be a great form of exercise. Leisurely walking (what most of us do in everyday life) meets most of the cardio criteria (large muscles, rhythmic nature, continuous movement); but at an easy pace, it typically will not meet the heart rate guideline—and therefore would not count as a true cardio workout. Only walking that is brisk enough to bring up your heart rate for an extended period of time truly offers the health and calorie-burning benefits of “cardio” exercise.

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A study published “BMC Complementary and Alternative Medicine” in 2007 found that practicing Hatha, a common form of yoga, resulted in low levels of physical activity equal to walking on a treadmill at about 2.5 mph. Although the goal of yoga is not a cardiorespiratory workout, more physically active asana practices may afford some mild aerobic benefits. “Bodywork and Movement Therapies” in January 2007 compared the heart-rate increasing effects of one of the most active forms of yoga, Ashtanga, to more gentle forms of yoga. The researchers found that Ashtanga did raise the heart rate significantly more than the quieter forms, but only to an average of 95 bpm, which represents low-intensity aerobic activity for people over age 50. One study conducted by Copenhagen City Heart in 2012 showed that women who jog live an average of 5.6 years longer, and males add 6.2 years to their lives with regular jogs. As for yoga, it appears to add to longevity by strengthening your core muscles. A 2005 study by the American Council on Exercise looked at the aerobic benefits and calories burned by a Hatha yoga class, which is considered one of the most beginner-friendly and popular forms of yoga.  The study concluded that while the yoga group showed numerous improvements in participants’ strength and endurance as well as improved balance and flexibility, they did not burn a significant amount of calories by practicing yoga. “In fact, one 50-minute session of Hatha yoga burns just 144 calories, similar to a slow walk,” according to researchers.  That’s about half the number of calories that traditional forms of cardio burn in the same amount of time. Total calories burned are a good indicator of how aerobically challenging any movement truly is. The harder it is, the more your heart rate elevates, and the more calories you burn—one sign of a good cardio workout. But this doesn’t mean that yoga isn’t worth the time, because exercise is about more than just burning calories.  It just means that you might want to reconsider swapping a yoga class for your cardio workout, and instead, use it as a complement to a well-rounded fitness routine.

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Oxygen uptake:

To measure the intensity of yoga compared to other activities, researchers turn to maximum oxygen uptake, or VO2 (the rate at which the body carries oxygen to active muscles). And the higher that rate, the harder the body is believed to be pushed. One study found that the VO2 rate of 10 young adults increased by 7 percent when hitting the yoga mat for eight weeks, while another put the elderly to the test, finding a VO2 boost of 11 percent in just six weeks. However, aerobic training (cardio) saw a 24 percent increase in oxygen uptake, signifying it may be best to be a part-time yogi, mixing up the mat with other forms of high-intensity aerobic training.

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Yoga exercise limitation:

While yoga can increase your heart rate, no research has ever indicated it is an effective source of cardiovascular exercise.  A 2005 study in the “Journal of Strength and Conditioning Research” indicated that you expend more oxygen walking than in doing basic yoga. A study conducted in 2012 at Colorado State University followed young adults who performed Bikram three days a week for eight weeks and found no cardiovascular benefit at all. Even strenuous power yoga burns only 237 calories over 50 minutes, according to the American Council on Exercise. Some yoga classes supplement the exercise with a cardiovascular component such as cycling or dancing, though the American Council on Exercise cautions against hybrid cardio-yoga classes, as they reduce the flexibility and balance benefits. Because of the importance of cardiovascular exercise in preventing heart disease, getting aerobic exercise should be your priority when planning a fitness regimen. That doesn’t mean, however, that yoga shouldn’t be part of that regimen. Aerobics pioneer and physician Kenneth Cooper recommends that people in their 30s or younger adopt routines that are 80 percent aerobic exercise with a 20 percent concentration on muscles and relaxation, such as yoga. As you get older, yoga can become a larger part of your fitness plan. As a bonus, the added flexibility it provides also will make you less likely to injure yourself during aerobic exercise.

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For decades, aerobic exercise—the type that raises your heart and breathing rates, such as running or cycling—has been touted by scientists as the gold standard in terms of the number of health benefits it brings. More energy, improved mood, lower risk of heart disease and certain cancers, better sleep, better thinking, better sex, and on and on. But as it turns out, there may be another form of exercise that does even more for you: yoga.

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In 2010, researchers at the University of Maryland School of Nursing published a comparative analysis of 81 studies that examined yoga’s health benefits and the health benefits of aerobic exercise. The researchers found yoga to be especially effective at reducing stress. This may not be news to those who practice yoga, but even die-hard enthusiasts will be surprised at the number of other health benefits yoga can confer—often to a larger degree than aerobic exercise. The researchers found that yoga outperformed aerobic exercise at improving balance, flexibility, strength, pain levels among seniors, menopausal symptoms, daily energy level, and social and occupation functioning, among other health parameters.  Neuroendocrinology researchers have found yoga can reduce stress and inflammation, as well as better regulate the autonomic nervous system than walking or simple exercise. (Yadav et al 2012, Streeter et al 2010, Streeter et al 2012)

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Experts believe that yoga can result in increased muscle strength and endurance because the regular stretching makes the muscles larger in size and also better able to extract and use the oxygen available more efficiently in the body. Also, regular practice of Pranayam increases lung capacity, allowing the lungs to expand fully as the ribs, shoulder and back areas become more flexible. Simply put – you can exercise for longer and reach maximum oxygen uptake levels, and also improve VO2 max levels. Of course, the longer one can hold such poses increases the benefits that come from rigorous yoga training.

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Yoga as Neuromuscular Exercise:

The American College of Sports Medicine classifies yoga as neuromuscular exercise, which is sometimes referred to as “functional” training. This type of exercise emphasizes your motor skills and helps hone balance and coordination. For older adults, neuromuscular exercise, such as yoga, can improve daily function and prevent falls. ACSM recommends you perform 20 to 30 minutes of this type of exercise daily. Many types of yoga could also fall under the rubric of flexibility training, which the ACSM also encourages you do as part of your weekly fitness routine. Yoga can help you meet the guidelines of performing stretches for the major muscle groups two to three times per week for 10- to 30-second holds to accumulate a total of 60 seconds total.

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Yoga better for your brain than exercise, 2013 study finds:

Twenty minutes of yoga is better for boosting brain activity than vigorous exercise for the same amount of time, a study has found. Researchers found that following yoga practice the participants were better able to focus their mental resources, process information quickly and more accurately and also learn, hold and update pieces of information more effectively than after performing an aerobic exercise bout.  “The breathing and meditative exercises aim at calming the mind and body and keeping distracting thoughts away while you focus on your body, posture or breath,” Professor Neha Gothe, who led the study, reported.  “Maybe these processes translate beyond yoga practice when you try to perform mental tasks or day-to-day activities.”  The study team said several factors could explain the results. Prof Gothe said: “Enhanced self-awareness that comes with meditational exercises is just one of the possible mechanisms. Besides, meditation and breathing exercises are known to reduce anxiety and stress, which in turn can improve scores on some cognitive tests.”

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Pilates and yoga:

In the 1920s, physical trainer Joseph Pilates introduced Pilates into America as a way to help injured athletes and dancers safely return to exercise and maintain their fitness. Since then, Pilates has been adapted to suit people in the general community. Pilates can be an aerobic and non-aerobic form of exercise. It requires concentration and focus, because you move your body through precise ranges of motion. Pilates lengthens and stretches all the major muscle groups in your body in a balanced fashion. It requires concentration in finding a centre point to control your body through movement. Each exercise has a prescribed placement, rhythm and breathing pattern. In Pilates, your muscles are never worked to exhaustion, so there is no sweating or straining, just intense concentration. The workout consists of a variety of exercise sequences that are performed in low repetitions, usually five to ten times, over a session of 45 to 90 minutes. Mat work and specialised equipment for resistance are used. Pilates is a method of exercising that lengthens and stretches all the major muscle groups in the body in a balanced fashion. Yoga brings the body and mind together and is built on three main elements – exercise, breathing and meditation. Yoga and Pilates both improve muscular and postural strength.

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Purported yoga benefits:

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Children:

There are five key areas where kids benefit from the practice of yoga, and each of them improves their overall well-being.

1. It enhances physical flexibility.

Yoga promotes physical strength because kids learn to use all of their muscles in new ways. Whether a pose is done standing, sitting, or lying down, each one can challenge various muscle groups while helping a child become aware of his body and how it efficiently functions.

2. It refines balance and coordination.

Balance is a key element of yoga. Balancing poses were created to promote mental and physical poise, as mental clarity and stability emerge from the effort of trying the poses. Even if a child has difficulty standing on one foot, she learns mental and physical balance if she can stay calm when she falls and when she gets up to try again. As children learn to improve their physical balance, they will be filled with a sense of accomplishment. Coordination is also closely tied to balance and promotes overall dexterity. Some yoga teachers and occupational therapists use finger yoga and other specialized techniques to help children with gross and fine motor coordination.

3. It develops focus and concentration.

The act of practicing poses encourages children to clear their mind and focus on the effort. As a result of this single focus to achieve a particular pose or stay balanced, yoga helps children to focus and concentrate in school and get better grades, several studies note.

4. It boosts Self-Esteem and confidence.

Yoga helps to instil confidence and to bring learning to children on an experiential level.

5. It strengthens the Mind-Body connection.

Yoga helps kids achieve a sound mind in a sound body by exercising the physical body and calming the mental spirit.

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Yoga is beneficial to children of all ages, but it has been found to be particularly so for kids with special needs. Studies have shown that yoga benefits children with autism and ADHD. NPR has reported that researchers surveyed teachers at a Bronx public school that had a daily yoga program and found that the program reduced kids’ aggressive behavior, social withdrawal, and hyperactivity, compared with a control group of kids with autism who did not practice yoga. Kristie Patten Koenig, Ph.D., an associate professor of occupational therapy at New York University who led the study, says that yoga was effective because it seemed to play to the strengths of kids with autism while also reducing stress. Autism Key, an autism support website, says that yoga helps address kids’ heightened anxiety, poor motor coordination, and weak self-regulation, something that otherwise is very difficult to do.

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Yoga benefits for adults:

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There are many benefits of yoga, including:

1. Stress relief:

The practice of yoga is well-demonstrated to reduce the physical effects of stress on the body. The body responds to stress through a fight-or-flight response, which is a combination of the sympathetic nervous system and hormonal pathways activating, releasing cortisol – the stress hormone – from the adrenal glands. Cortisol is often used to measure the stress response. Yoga practice has been demonstrated to reduce the levels of cortisol. Most yoga classes end with savasana, a relaxation pose, which further reduces the experience of stress.

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2. Pain relief:

Yoga can ease pain. Studies have shown that practicing yoga asanas (postures), meditation or a combination of the two, reduced pain for people with conditions such as cancer, multiple sclerosis, auto-immune diseases as well as arthritis, back and neck pain and other chronic conditions.

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3. Better breathing:

Yoga includes breathing practices known as pranayama, which can be effective for reducing our stress response, improving lung function and encouraging relaxation. Many pranayamas emphasize slowing down and deepening the breath, which activates the body’s parasympathetic system, or relaxation response. By changing our pattern of breathing, we can significantly affect our body’s experience of and response to stress. This may be one of the most profound lessons we can learn from our yoga practice.

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4. Flexibility:

Yoga can improve flexibility and mobility and increase range of motion. Over time, the ligaments, tendons and muscles lengthen, increasing elasticity. Yoga is a wonderful tool to increase joint flexibility. Factors like sedentary lifestyles, our jobs and even our age can have strong effects on our flexibility and without it, poor postural habits and incorrect movements start to appear in our daily tasks (like going from sitting to standing and lifting). These habits, because of perceived, real or anticipated aches and stiffness can lead to joint immobility. A regular Yoga practice can have wonderful restorative effects on your joints, muscles, organs and mind.

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5. Increased strength:

Yoga asanas use every muscle in the body, increasing strength literally from head to toe. A regular yoga practice can also relieve muscular tension throughout the whole body.

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6. Weight management:

While most of the evidence for the effects of yoga on weight loss is anecdotal or experiential, yoga teachers, students and practitioners across the country find that yoga helps to support weight loss. Many teachers specialize in yoga programs to promote weight management and find that even gentle yoga practices help support weight loss. People do not have to practice the most vigorous forms of yoga to lose weight. Yoga encourages development of a positive self-image, as more attention is paid to nutrition and the body as a whole. A study from the Journal of Alternative Therapies in Health and Medicine found that regular yoga practice was associated with less age-related weight gain. The lifestyle study of 15,500 adults in their 50’s covered 10 years of participants’ weight history, physical activity, medical history and diet.

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7. Improved circulation:

Yoga helps to improve circulation by efficiently moving oxygenated blood to the body’s cells.

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8. Cardiovascular conditioning:

Even a gentle yoga practice can provide cardiovascular benefits by lowering resting heart rate, increasing endurance and improving oxygen uptake during exercise.

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9. Massaging of all Organs of the Body:

Yoga is perhaps the only form of activity which massages all the internal glands and organs of the body in a thorough manner, including those – such as the prostate – that hardly get externally stimulated during our entire lifetime. Yoga acts in a wholesome manner on the various body parts. This stimulation and massage of the organs in turn benefits us by keeping away disease and providing a forewarning at the first possible instance of a likely onset of disease or disorder.

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10. Complete Detoxification:

By gently stretching muscles and joints as well as massaging the various organs, yoga ensures the optimum blood supply to various parts of the body. This helps in the flushing out of toxins from every nook and cranny as well as providing nourishment up to the last point. This leads to benefits such as delayed ageing, energy and a remarkable zest for life.

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11. Boost Immunity:

A recent Norwegian study found that yoga practice results in changes in gene expression that boost immunity at a cellular level. And it doesn’t take long: The researchers believe the changes occurred while participants were still on the mat, and they were significantly greater than a control group who went on a nature hike while listening to soothing music. Yoga also helps to boost immunity by simply increasing overall health, says Mitchel Bleier, a yoga teacher of 18 years and owner of Yogapata in Connecticut. “As you breathe better, move better and circulate better, all the other organs function better.”

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12. Ease Migraines:

Research shows that migraine sufferers have fewer and less painful migraines after three months of yoga practice. The cause of migraines isn’t fully understood, but it could be a combination of mental stressors and physical misalignment that create migraines and other issues. Hunching over a computer or cell phone with your shoulders up and head forward causes overlifting of your trapezius and tightening of the neck. This pulls the head forward and creates muscle imbalances that can contribute to headaches and migraines.

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13. Boost Sexual Performance:

Studies have found that 12 weeks of yoga can improve sexual desire, arousal, performance, confidence, orgasm and satisfaction for both men and women. How? Physically, yoga increases blood flow into the genital area, which is important for arousal and erections and strengthens the “moola bandha,” or pelvic floor muscles. Mentally, the breathing and mind control involved with the practice can also improve performance.

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14. Sleep Better:

Researchers from Harvard found that eight weeks of daily yoga significantly improved sleep quality for people with insomnia. And another study found that twice-weekly yoga sessions helped cancer survivors sleep better and feel less fatigued. This can be attributed to yoga’s ability to help people deal with stress. Breathing and mental exercises allow the mind to slow down, so you’re going to start to see yourself sleep better.

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15. Fight Food Cravings:

Researchers from the University of Washington found that regular yoga practice is associated with mindful eating, an awareness of physical and emotional sensations associated with eating. By causing breath awareness, regular yoga practice strengthens the mind-body connection. The awareness can help you tune in to emotions involved with certain cravings, and yoga breathing exercises can help you slow down and make better choices when cravings strike.

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For 5,000 years, hardcore yoga practitioners have been touting yoga’s mental and physical powers. Luckily, you don’t have to be an expert to reap the benefits — adding just a few poses to your daily routine can help your health in all kinds of unexpected ways. On a physical level, yoga helps improve flexibility, strength, balance, and endurance. On an energetic level, yoga teaches you how to cope better with stress by cultivating a sense of ease in both active or passive poses. On a psychological level, yoga helps to cultivate mindfulness by shifting your awareness to the sensations, thoughts, and emotions that accompany a given pose or exercise.

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Potential health benefits for adults:

While much of the medical community regards the results of yoga research as significant, others point to many flaws which undermine results. Much of the research on yoga has taken the form of preliminary studies or clinical trials of low methodological quality, including small sample sizes, inadequate blinding, lack of randomization, and high risk of bias. Long-term yoga users in the United States have reported musculoskeletal and mental health improvements, as well as reduced symptoms of asthma in asthmatics. There is evidence to suggest that regular yoga practice increases brain GABA levels, and yoga has been shown to improve mood and anxiety more than some other metabolically-matched exercises, such as walking. The three main focuses of Hatha yoga (exercise, breathing, and meditation) make it beneficial to those suffering from heart disease. Overall, studies of the effects of yoga on heart disease suggest that yoga may reduce high blood-pressure, improve symptoms of heart failure, enhance cardiac rehabilitation, and lower cardiovascular risk factors. For chronic low back pain, specialist Yoga for Healthy Lower Backs has been found 30% more beneficial than usual care alone in a UK clinical trial. Other smaller studies support this finding. The Yoga for Healthy Lower Backs programme is the dominant treatment for society (both cheaper and more effective than usual care alone) due to 8.5 fewer days off work each year. A research group from Boston University School of Medicine also tested yoga’s effects on lower-back pain. Over twelve weeks, one group of volunteers practiced yoga while the control group continued with standard treatment for back pain. The reported pain for yoga participants decreased by one third, while the standard treatment group had only a five percent drop. Yoga participants also had a drop of 80% in the use of pain medication. There has been an emergence of studies investigating yoga as a complementary intervention for cancer patients. Yoga is used for treatment of cancer patients to decrease depression, insomnia, pain, and fatigue and to increase anxiety control. Mindfulness Based Stress Reduction (MBSR) programs include yoga as a mind-body technique to reduce stress. A study found that after seven weeks the group treated with yoga reported significantly less mood disturbance and reduced stress compared to the control group. Another study found that MBSR had showed positive effects on sleep anxiety, quality of life, and spiritual growth in cancer patients. Yoga has also been studied as a treatment for schizophrenia. Some encouraging, but inconclusive, evidence suggests that yoga as a complementary treatment may help alleviate symptoms of schizophrenia and improve health-related quality of life. Implementation of the Kundalini Yoga Lifestyle has shown to help substance abuse addicts increase their quality of life according to psychological questionnaires like the Behavior and Symptom Identification Scale and the Quality of Recovery Index. Yoga has been shown in a study to have some cognitive functioning (executive functioning, including inhibitory control) acute benefit.

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Yoga as complementary and alternative medicine (CAM) therapy:

There is a growing body of research into the efficacy of yoga and meditation practices, either stand-alone or as an adjunct to conventional therapy, for a range of health issues and medical conditions. Yoga has long been associated with musculoskeletal therapy. This is well supported in the literature by studies demonstrating the benefit of yoga practices for acute and chronic pain, lower back pain, joint pain, osteoarthritis and rheumatoid arthritis, functional disability and pain medication usage. However, there is also promising evidence for the use of yoga and meditation for mental health issues such as stress management, non-psychotic mood, high trait anxiety and generalized anxiety disorders and mild-to-moderate depression,  usually as part of a multi-disciplinary approach. For women who practice yoga, there is good evidence of assistance with pre-menstrual syndrome and menopausal symptoms, while pre-natal yoga has been shown to lower rates of pre-term labor, increase birth weights and reduce pregnancy-related complications.  Regular yoga practice has also been shown to positively impact on risk factors for cardiovascular disease and diabetes such as hypertension, obesity, hyperlipidemia, glucose tolerance, insulin sensitivity, oxidative stress, sympathetic activation and cardiovagal function.  Intensive lifestyle change, based on yogic lifestyle, including a low fat vegetarian diet, non-smoking, moderate exercise, stress management and psychosocial support, has been shown to reverse coronary artery stenosis, to reduce recurrence of adverse cardiovascular events and reduce angina pain. Other conditions for which yoga has shown some benefit in the literature include gastrointestinal, respiratory, cognitive function and neurological, geriatric quality of life and symptomatic relief for cancer sufferers.

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Ayurveda and yoga:

With its origin in the Vedas, Ayurveda also incorporates certain principles of yoga within its folds. With its main focus on physiological balance and cleansing, Ayurveda which is one of the most ancient systems of healing; makes use of medication based on herbs and natural resources apart from bringing about suitable modifications to lifestyle and diet management. Besides these, Ayurveda also includes yoga or union as one of its therapeutic tools. Yoga which makes for the union of mind, body and soul, is another naturopathic healing tool. Paving way for the best possible integration of mental, physical and spiritual forces of energy ,yoga includes in its scope certain postures or ‘asanas’; breathing exercises or ‘pranayama’; and meditation which is supposed to be giving way to perfect bliss. Both Ayurveda and ‘yoga’ are similarly geared to the prospect of healing and preventing the occurrence of disease by striking in the human system a perfect balance amongst its three fold natural elements of fire, phlegm and air. Since time immemorial, with their inception during the Vedic Age, the twin concepts of Ayurveda and yoga have been going hand in hand. To focus particularly on yoga, its multifarious benefits apart from therapeutic healing include mental and physical rejuvenation, increased focus on things, prolonged existence and mental calm. Yogic postures linked with Ayurvedic healing are numerously manifold in terms of their technical modes and therapeutic use. Both yoga and ayurveda are based upon the principles of trigunas (sattva, rajas and tamas) and the panchamahabuthas (earth, air, fire, water, space). Yoga and ayurveda also encompass an understanding of how the body works (Dosha-Dhatu-Mala/humor-tissue-waste material theory) and the effect that food and medicines have on the body (Rasa-Veerya-Vipaka/taste-energy-post digestive effect concept). Both of these sciences have eight branches: Ashtanga yoga and Ashtanga ayurveda. The two have a common understanding of health of the body being dependent on the health and balance of the mind. They share virtually the same metaphysical anatomy and physiology, which consists of 72,000 nadis (subtle channels), seven main chakras (energy centers), five bodily sheaths and the kundalini shakti (energy). In treatment, both yoga and ayurveda advocate for the regular practice of pranayama and meditation as well as the use of herbs, body purification procedures, food and chanting of mantras for physical and mental health. In yoga, the body purification procedures have been explained as ‘Satkriyas’ whereas in ayurveda they are known as ‘Panchakarma’. Both recognize that keeping the body healthy is vital for fulfilling the four aims of life: dharma (duty), artha (wealth), kama (desire), and moksha (liberation). It is quite a revelation to see how yoga and ayurveda are interrelated.

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Scientific mechanisms of yoga effects:

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Yoga and stress:

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The figure above shows impact of stress on the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic nervous system. Research has described the negative effects of stress on the body. Linked to the release of the stress-hormones adrenalin and cortisol, stress raises the heart rate and blood pressure, weakens immunity and lowers fertility. By contrast, the state of relaxation is linked to higher levels of feel-good chemicals such as serotonin and to the growth hormone which repairs cells and tissue. Indeed, studies show that relaxation has virtually the opposite effect, lowering heart rate, boosting immunity and enabling the body to thrive.

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The autonomic nervous system:

To appreciate the role of stress in disease and of relaxation in prevention and recovery, it’s important to understand the function of the autonomic nervous system (ANS), which controls the function of the heart, liver, intestines, and other internal organs. The ANS has two branches that work in conjunction: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). In general, when activity is high in the SNS, it is lower in the PNS, and vice versa. The SNS, in conjunction with such stress hormones as adrenaline and cortisol, initiate a series of changes in the body, including raising blood pressure, heart rate, and blood sugar levels. These changes help a person deal with a crisis situation. They mean more energy and more blood and oxygen flowing to the large muscles of the trunk, arms, and legs, allowing the person to run from danger or do battle (the so-called “fight-or-flight” response).  As the catch phrase suggests, the sympathetic division prepares your body for action, priming you to react to dangerous or stressful conditions. Your liver releases glucose (blood sugar), your breathing speeds up, air passages in your lungs widen, your heart pounds, and systolic blood pressure rises. Those responses are vital for survival when you’re faced with an immediate threat. The parasympathetic nervous system brings us back to normal when danger has passed. Because exercise is also a stressor, albeit a controlled one, the same mechanisms kick in when you’re doing cardio. Problems start when stress becomes overwhelming or overly prolonged. Stressors like car alarms, stock market crashes and tax deadlines aren’t physically threatening, yet the sympathetic nervous system reacts as if they were. And although short-lived spikes in glucose, breathing rate or blood pressure are healthy and necessary when dealing with a real threat, if they become chronic they cause serious health problems. The PNS, in contrast, tends to slow the heart and lower the blood pressure, allowing recovery after a stressful event. Blood flow that was diverted away from the intestines and reproductive organs, whose function isn’t essential in an emergency, returns. In contrast to fight or flight, these more restorative functions can be thought of as “rest and digest.” They are also sometimes dubbed the relaxation response. While the sympathetic nervous system responds to external events, marshalling resources to deal with threats, the parasympathetic system maintains the body’s normal internal environment, what French physiologist Claude Bernard called the “milieu interieur.” Many aspects of that environment must be maintained within narrow limits for us to function and stay healthy, a process termed homeostasis. For example, the parasympathetic system stimulates digestion, keeps heart rate and blood pressure within normal levels, and promotes healthy immune function. Many yoga practices, including quiet asana, slow breathing, meditation, and guided imagery, increase activation of the PNS and lead to mental relaxation. Yoga techniques are more than just relaxation, however. Practices like vigorous sun salutations, kaphalabhati breathing, and breath retentions actually activate the SNS. One of yoga’s secrets, documented in research from the Swami Vivekananda Yoga Research Foundation near Bangalore, is that more active practices followed by relaxing ones lead to deeper relaxation than relaxing practices alone.

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The stress and stress-induced disorders like hypertension and angina are fast growing epidemics and bane of “modern” society. The holistic science of yoga is the best method for prevention as well as management of stress and stress-induced disorders. Numerous studies have shown yoga to have an immediate down-regulating effect on both the HPA axis responses to stress. Effectiveness of yoga against stress management is well established. It was also found that brief yoga-based relaxation training normalizes the function of the autonomic nervous system by deviating both sympathetic and parasympathetic indices toward more “normal” middle region of the reference values. Studies show that yoga decreases levels of salivary cortisol, blood glucose, as well as plasma rennin levels, and 24-h urine nor-epinephrine and epinephrine levels. Yoga significantly decreases heart rate and systolic and diastolic blood pressures. These studies suggest that yoga has an immediate quieting effect on the HPA axis response to stress. While the precise mechanism of action has not been determined, it has been hypothesized that some yoga exercises cause a shift toward parasympathetic nervous system dominance, possibly via direct vagal stimulation. Shapiro et al. noted significant reductions in low-frequency heart rate variability – a sign of sympathetic nervous system activation – in depressed patients following an 8-week yoga intervention. Regardless of the pathophysiologic pathway, yoga has been shown to have immediate psychological effects: decreasing anxiety and increasing feelings of emotional, social, and spiritual well-being. Several literature reviews have been conducted that examined the impact of yoga on specific health conditions including cardiovascular disease metabolic syndrome, diabetes, cancer, and anxiety.

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A small but intriguing study further characterizes the effect of yoga on the stress response. In 2008, researchers at the University of Utah showed that among control subjects and yoga practitioners, by functional MRIs, that yoga practitioner had the highest pain tolerance and lowest pain-related brain activity during the MRI. The study underscores the value of techniques, such as yoga, that can help a person regulate their stress and, therefore, pain responses. Tooley et al. found significantly higher plasma melatonin levels in experienced mediators in the period immediately following meditation compared with the same period at the same time on a control night. It was concluded that meditation can affect plasma melatonin levels. It remains to be determined whether this is achieved through decreased hepatic metabolism of the hormone or via a direct effect on pineal physiology. Either way, facilitation of higher physiological melatonin levels at appropriate times of day might be one avenue through which the claimed health promoting effects of meditation occur. In another study, Harinath et al. evaluated the effects of 3 month hatha yoga practice and Omkar meditation on melatonin secretion in healthy subjects. Yoga group subjects practiced selected yogic asanas for 45 min and pranayama for 15 min during the morning, whereas during the evening hours these subjects performed preparatory yogic postures for 15 min, pranayama for 15 min, and meditation for 30 min daily for 3 months. Results showed that yoga practice for 3 months resulted in an improvement in cardiorespiratory performance and psychological profile. The plasma melatonin also showed an increase after 3 months of yogic practice. Also, the maximum night time melatonin levels in the yoga group showed a significant correlation with well-being score. These observations suggest that yogic practices can be used as psychophysiologic stimuli to increase endogenous secretion of melatonin, which, in turn, might be responsible for improved sense of well-being. In some other studies, it has been found that subjects trained in yoga can achieve a state of deep psychosomatic relaxation associated with highly significant decrease in oxygen consumption within 5 min of practicing savitri pranayama (a slow, rhythmic and deep breathing) and shavasana.

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How does heart rate variability fit into this?

The primary pacemaker of the heart is the sino-atrial node, a region of specialized cardiac muscle cells in the right atrium of the heart. The sino-atrial node rhythmically fires at a rate of about 60 to 100 beats per minutes, creating electrical signals that propagate throughout the heart, stimulating contraction. Inputs from the autonomic nervous system modify that basic sinus rhythm, particularly inputs from the vagus nerve, the major nerve of the parasympathetic system. When vagal (parasympathetic) tone increases, heart rate slows down. As that input is withdrawn, the sino-atrial node returns to its baseline firing rate. When the sympathetic system kicks in, heart rate can speed up above 100 beats per minute. Left to its own devices, the sino-atrial node would beat out a regular rhythm like a metronome. But, largely because of vagal stimulation, a healthy person’s heart rate actually varies considerably under normal circumstances. You may be able to feel the normal variation in your heartbeat that accompanies breathing—termed respiratory sinus arrhythmia. Take a few long, slow breaths and notice how your heart rate accelerates as you inhale and decreases as you exhale. Slow breathing increases respiratory sinus arrhythmia, making it easier to sense, but even when you’re sitting quietly and breathing normally, your heart rate varies with the breathing cycle. As you exhale, parasympathetic tone increases and your heart rate slows. When you inhale, there is a decrease in vagal input, and your heart rate speeds up. It’s not clear why that is, but one theory suggests that soaking the lungs with extra blood during an inhalation uses the heart’s output more efficiently. Whatever the reason, the fact that heart rate variability is tied to autonomic tone makes it a useful marker for measuring the balance between the sympathetic and parasympathetic divisions. Today researchers use complex mathematical models to identify several frequency components of heart rate variability. The low-frequency range is generally a marker of sympathetic tone while the high-frequency band is linked to parasympathetic activation. The ratio between the two describes the relative balance between the two autonomic divisions. In a study, Santaella and his colleagues found that the group who practiced pranayama experienced a reduction in the low-frequency band as well as in the low-to-high-frequency ratio, suggesting a shift from a sympathetic to a more parasympathetic state. In other words, the bhastrika practitioners were less stressed than their counterparts in the control group. There is evidence that yoga practices help increase heart rate variability, an indicator of the body’s ability to respond to stress more flexibly. A growing body of research on heart-rate variability and yoga provides evidence that the practice can help people in their quest for healthier stress responses. One of the first studies was conducted at Newcastle University in England and published in 1997 in the European Journal of Clinical Investigation. Researchers found that six weeks of practicing hatha yoga increased the activation of the parasympathetic nervous system (the calming side) without decreasing the influence of the sympathetic (the arousing side). Researchers took 26 healthy but sedentary adults and randomly split them into two groups. One group was given an aerobic exercise program, the other a yoga regimen that included two 90-minute sessions per week with breathing, poses, and relaxation. In the week following the six-week intervention, the yoga participants were reported to have higher heart-rate variability (and a lower resting heart rate, another indicator of well-being) after the study than before. The aerobics group showed no significant changes. A second study, done by researchers at the University of Schleswig-Holstein in Germany and published in 2007 in the journal Evidence-Based Complementary and Alternative Medicine, suggests that even a single session of yoga practice can encourage the nervous system to find flexibility and balance. Researchers hooked up 11 healthy yoga practitioners to instruments that recorded their heart-rate variability over 24 hours. During that time, participants did 60 minutes of active Iyengar Yoga poses and 30 minutes of restorative poses. Heart-rate variability increased during the yoga session, and—as in the previous study—this change was driven by the increased influence of the parasympathetic nervous system, not by changes to the sympathetic system. In other words, after yoga practice, participants weren’t just more relaxed; they were in a state of autonomic balance and flexibility driven by the parasympathetic—which is exactly the type of balance and flexibility that predicts greater resilience to stress. This study provides promising evidence that a yoga practice can prepare you to meet life’s challenges, not just recover from them.

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Yoga and neuroendocrine:

Over time, the constant state of hypervigilence resulting from repeated firing of the HPA axis can lead to deregulation of the system and ultimately diseases such as obesity, diabetes, autoimmune disorders, depression, substance abuse, and cardiovascular disease. A growing body of evidence supports the belief that yoga benefits physical and mental health via down-regulation of the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic nervous system (SNS). Yoga helps dampen the body’s stress response by reducing levels of the hormone cortisol, which not only fuels our split-second stress reactions, but it can wreak havoc on the body when one is chronically stressed. So reducing the body’s cortisol level is generally considered a good thing. Reducing circulating cortisol removes a barrier to effective immune function, so yoga could help prevent illness by boosting immunity. Yoga also boosts levels of the feel-good brain chemicals like GABA, serotonin, and dopamine, which are responsible for feelings of relaxation and contentedness, and the way the brain processes rewards. All three neurotransmitters are the targets of various mood medications like antidepressants (e.g., SSRIs) and anxiolytic (anti-anxiety) drugs.

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Slow deep breathing in yoga:

It is known that the regular practice of breathing exercise (pranayama) increases parasympathetic tone, decreases sympathetic activity, improves cardiovascular and respiratory functions, decreases the effect of stress and strain on the body and improves physical and mental health. It has been demonstrated that yoga training that includes pranayama, improves autonomic and pulmonary functions in asthma patients. Regular practice of breathing exercise is shown to improve autonomic functions by decreasing sympathetic activity or by increasing vagal tone. The improvement of parasympathetic activity following practice of slow breathing exercise in may possibly be due to increased oxygenation of tissues due to increased alveolar ventilation. As oxygenation does not improve in fast breathing due to decreased alveolar ventilation, no significant change in autonomic activity was observed in fast breathing group. Pranayamic breathing has been shown to contribute to a physiologic response characterized by the presence of decreased oxygen consumption, decreased heart rate, and decreased blood pressure, as well as increased theta wave amplitude in EEG recordings, increased parasympathetic activity accompanied by the experience of alertness and reinvigoration. The mechanism of how pranayamic breathing interacts with the nervous system affecting metabolism and autonomic functions remains to be clearly understood.

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Yoga and genes:

Harvard researchers found that yoga, meditation and even repetitive prayer and mantras all induced the relaxation effect.  A comprehensive scientific study showing that deep relaxation changes our bodies on a genetic level has just been published. What researchers at Harvard Medical School discovered is that, in long-term practitioners of relaxation methods such as yoga and meditation, far more ”disease-fighting genes” were active, compared to those who practised no form of relaxation. In particular, they found genes that protect from disorders such as pain, infertility, high blood pressure and even rheumatoid arthritis were switched on. The changes, say the researchers, were induced by what they call ”the relaxation effect”, a phenomenon that could be just as powerful as any medical drug but without the side effects. ”We found a range of disease-fighting genes were active in the relaxation practitioners that were not active in the control group,” Dr Herbert Benson, associate professor of medicine at Harvard Medical School, who led the research, says. The good news for the control group with the less-healthy genes is that the research didn’t stop there. The experiment, which showed just how responsive genes are to behaviour, mood and environment, revealed that genes can switch on, just as easily as they switch off. ”Harvard researchers asked the control group to start practising relaxation methods every day,” says Jake Toby, hypnotherapist at London’s BodyMind Medicine Centre, who teaches clients how to induce the relaxation effect. ”After two months, their bodies began to change: the genes that help fight inflammation, kill diseased cells and protect the body from cancer all began to switch on.” More encouraging still, the benefits of the relaxation effect were found to increase with regular practice: the more people practised relaxation methods such as meditation or deep breathing, the greater their chances of remaining free of arthritis and joint pain with stronger immunity, healthier hormone levels and lower blood pressure. Benson believes the research is pivotal because it shows how a person’s state of mind affects the body on a physical and genetic level. It might also explain why relaxation induced by meditation or repetitive mantras is considered to be a powerful remedy in traditions such as Ayurveda in India or Tibetan medicine.

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A recent study conducted by the University of Oslo asked ten participants to attend a week-long yoga retreat in Germany. For the first two days, participants spent two hours practicing yoga, including yogic postures, yogic breathing exercises, and meditation. For the next two days, they spent that same time period going on an hour-long nature walk and then listening to either jazz or classical music. “The researchers found that the nature walk and music-driven relaxation changed the expression of 38 genes in these circulating immune cells. In comparison, the yoga produced changes in 111.” Fahri Saatcioglu of the University of Oslo, whose team conducted the research, wrote in the study that “the data suggest that previously reported (therapeutic) effects of yoga practices have an integral physiological component at the molecular level, which is initiated immediately during practice.” Compared with wellness activities like exercise and listening to music, yoga’s impact was far more widespread, which indicates the practice “may have additional effects over exercise plus simple relaxation in inducing health benefits through differential changes at the molecular level.”

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Yoga and chromosomes:

A study of breast cancer survivors showed an increase in telomere length after participating in a weekly meditation program for 12 weeks. The participants were split into three groups. The first group was taught mindfulness meditation techniques and a hatha yoga sequence during a series of group sessions and a retreat; they were also instructed to meditate and practice yoga for forty-five minutes a day at home. The women in the second group were sent to group therapy sessions led by clinical psychologists or social workers. These women met for 90 minutes weekly over the course of 12 weeks, sharing feelings and developing relationships with one another with the goal of teaching coping skills and developing a mutual support system. The third group functioned as the control group; the women in this group were assigned to a single, six-hour “stress management seminar.”  Significantly, the study found that the women who received ongoing treatment—both the yoga/meditation group and the therapy group—maintained telomere length, while the women in the control group showed shortened telomeres. Telomeres protect chromosomes by keeping them intact and preventing them from breaking down or fusing with another chromosome. Longer telomeres are indicative of healthy cells, while shortened telomeres are a type of cell degeneration.  Shortened telomeres are also associated with diseases such as heart disease, diabetes, osteoporosis, and Alzheimer’s and longer telomeres are generally thought to help protect us from disease.

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My view:

Inside the nucleus of a cell, our genes are located on twisted, double-stranded molecules of DNA called chromosomes. A telomere is a region of repetitive nucleotide sequences at each end of a chromosome. It protects the end of the chromosome from deterioration or from fusion with neighbouring chromosomes. Telomeres have been compared with the plastic tips on shoelaces because they prevent chromosome ends from fraying and sticking to each other, which would scramble an organism’s genetic information to cause cancer, other diseases or death. Yet, each time a cell divides, the telomeres get shorter. When they get too short, the cell no longer can divide and becomes inactive or “senescent” or dies. Once the telomeres are depleted, due to the cell dividing many times, it will no longer divide having reached its Hayflick limit. This process does not take place in cancer cells due to an enzyme called telomerase. This enzyme maintains telomere length, which results in the telomeres of cancer cells never shortening. This gives these cells infinite replicative potential.  A proposed treatment for cancer is the usage of telomerase inhibitors that would prevent the restoration of the telomere, allowing the cell to die like other body cells. While lengthened telomeres are helpful to prevent aging and degenerative disorders, lengthened telomeres would worsen cancer. Here yoga is increasing telomere length in cancer patients which would worsen cancer rather than bringing good health.

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Yoga and brain:

Meditation and brain:

A Harvard University study conducted a few years ago, demonstrated that as little as 27 minutes of meditation per day changed the physical structure of the brain in just eight weeks. Participants in the study group who practiced meditation had an increase in grey matter in the parts of the brain associated with learning, memory, self-awareness and compassion, and a decrease in grey matter in areas associated with anxiety and stress. None of these changes were present in the control group. While other studies have been able to replicate these results, some have also shown that different styles of meditation may affect the body in different ways. In one study, the brain activity of participants practicing either Vajrayana or Theravada meditation was measured. The two types of Theravada meditation, Shamatha and Vipassana, resulted in increased relaxation, seen through an increase in parasympathetic nervous system responses. Those practicing one of the two types of Vajrayana meditation, visualization and Rig-pa, showed increased arousal, seen through increased sympathetic nervous system activity.

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Yoga changes the Brain: a 2013 study:

Using MRI scans, Villemure detected more grey matter—brain cells—in certain brain areas in people who regularly practiced yoga, as compared with control subjects. “We found that with more hours of practice per week, certain areas were more enlarged,” Villemure says, a finding that hints that yoga was a contributing factor to the brain gains. Yogis had larger brain volume in the somatosensory cortex, which contains a mental map of our body, the superior parietal cortex, involved in directing attention, and the visual cortex, which Villemure postulates might have been bolstered by visualization techniques. The hippocampus, a region critical to dampening stress, was also enlarged in practitioners, as were the precuneus and the posterior cingulate cortex, areas key to our concept of self. All these brain areas could be engaged by elements of yoga practice, Villemure says. The yogis dedicated on average about 70 percent of their practice to physical postures, about 20 percent to meditation and 10 percent to breath work, typical of most Western yoga routines. Villemure presented the work in November 2013 at the annual meeting of the Society for Neuroscience in San Diego.

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Fluid intelligence and brain functional organization in aging yoga and meditation practitioners: a 2014 study:

Numerous studies have documented the normal age-related decline of neural structure, function, and cognitive performance. Preliminary evidence suggests that meditation may reduce decline in specific cognitive domains and in brain structure. Here authors extended this research by investigating the relation between age and fluid intelligence and resting state brain functional network architecture using graph theory, in middle-aged yoga and meditation practitioners, and matched controls. In this fMRI study, researchers observed greater resting state functional connectivity (i.e., an index of brain connectivity captured when one is not actively performing a task) in similar brain regions among Kripalu yoga and meditation practitioners when compared to non-practitioners. Dr. Tim Gard and colleagues hypothesize that the findings may help to explain the improved mental health and well-being commonly seen among those who practice yoga and meditation (findings were similar in both groups). The researchers used fMRI to compare the resting state brain functional connectivity of 16 Kripalu yoga practitioners, 16 Vipassana meditators and 15 controls (i.e., those with minimal lifetime yoga/meditation practice). Meditators, with an average age of 54, were all trained in insight meditation/ Vipassana/ “mindfulness” and had an average of about 7,500 hours of practice w/a standard deviation of 5,700 hrs. Yoga folk, w/an average age of 49, were trained in Kripalu Yoga and had an average of about 13,500 hrs of experience w/a standard deviation of about 10,000 hrs. The study employed graph theoretical analysis, a “hot” area now in modelling the complexity of brain functional connectivity, to assess the effects of aging on network integration and fluid intelligence as well as “resilience” or the brain’s ability to respond to damage from brain lesions and neuronal death.  Both yogis and meditators showed much less decline in fluid intelligence with age than did the controls – the yogis appearing to do better than the meditators.   However, due to the large data spread, while the difference from controls was significant, the difference between yogis and meditators was not statistically significant. The researchers found the caudate nucleus (i.e., a brain structure linked with learning and communication) different in contemplative practitioners and controls. Their findings revealed stronger connectivity between the caudate nucleus and other brain regions (i.e., frontal, temporal and parietal) in meditators and yogis than in controls. To test whether these findings could be replicated, the same analysis was conducted on a second sample of meditators versus controls, with remarkably consistent findings. The caudate is implicated as a key aspect of brain circuits (i.e., basal ganglia-thalamocortical) related to goal directed (rather than habitual) learning. Thus, the researchers theorize that the greater connectivity observed between the caudate and the prefontal cortex may explain positive associations between mindfulness and cognitive and behavioral flexibility (i.e., the ability to change what you are thinking about, and how you are thinking about it, and the ability to flexibly adapt your behavior). Fluid intelligence declined slower in yoga practitioners and meditators combined than in controls. Resting state functional networks of yoga practitioners and meditators combined were more integrated and more resilient to damage than those of controls. Furthermore, mindfulness was positively correlated with fluid intelligence, resilience, and global network efficiency. These findings reveal the possibility to increase resilience and to slow the decline of fluid intelligence and brain functional architecture and suggest that mindfulness plays a mechanistic role in this preservation.

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Yoga and Depression:

Low brain levels of the neurotransmitter GABA are often found in people with depression; SSRIs, electroconvulsive therapy, and now yoga, it seems, can boost GABA. Preliminary research out of the Boston University School of Medicine and Harvard’s McLean Hospital found that healthy subjects who practiced yoga for one hour had a 27 percent increase in levels of GABA compared with a control group that simply sat and read for an hour. This supports a growing body of research that’s proving yoga can significantly improve mood and reduce the symptoms of depression and anxiety.

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Increased dopamine tone during meditation-induced change of consciousness (Yoga Nidra):

This is the first in vivo demonstration of an association between endogenous neurotransmitter release and conscious experience. Using 11C-raclopride PET authors demonstrated increased endogenous dopamine release in the ventral striatum during Yoga Nidra meditation. Yoga Nidra is characterized by a depressed level of desire for action, associated with decreased blood flow in prefrontal, cerebellar and subcortical regions, structures thought to be organized in open loops subserving executive control. In the striatum, dopamine modulates excitatory glutamatergic synapses of the projections from the frontal cortex to striatal neurons, which in turn project back to the frontal cortex via the pallidum and ventral thalamus. The present study was designed to investigate whether endogenous dopamine release increases during loss of executive control in meditation. Participants underwent two 11C-raclopride PET scans: one while attending to speech with eyes closed, and one during active meditation.

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Yoga and inflammation:

New research suggests a regular practice of yoga may lower an inflammatory protein that is normally linked to aging and stress.  The study, done by Ohio State University researchers and just reported in the journal Psychosomatic Medicine, showed that women who routinely practiced yoga had lower amounts of the cytokine interleukin-6 (IL-6) in their blood. The women also showed smaller increases in IL-6 after stressful experiences than did women who were the same age and weight but who were not yoga practitioners. IL-6 is an important part of the body’s inflammatory response and has been implicated in heart disease, stroke, type 2 diabetes, arthritis and a host of other age-related debilitating diseases. Reducing inflammation may provide substantial short- and long-term health benefits, the researchers suggest. “In addition to having lower levels of inflammation before they were stressed, we also saw lower inflammatory responses to stress among the expert yoga practitioners in the study,” explained Janice Kiecolt-Glaser, professor of psychiatry and psychology and lead author of the study. “Hopefully, this means that people can eventually learn to respond less strongly to stressors in their everyday lives by using yoga and other stress-reducing modalities.”

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Summary of scientific yoga mechanisms:

A literature overview employs a systematic search to include articles of clinical investigation, synthesis or review that focus on potential underlying mechanisms for yoga’s effect on prevention and treatment of disease. Results indicate that strong evidence exists for yoga mechanisms in areas of hormonal regulation, sympathetic activity in the nervous system and the betterment of physical health attributes such as improved balance, flexibility, strength and cardiorespiratory health. Empirical evidence exists for effect of yoga on metabolism, circulation, behaviour, oxidative stress, inflammation and psychological thought processes, while hypothesis exist in immunology, nerve conduction and bioelectromagnetism.

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Scientific studies on yoga and yoga therapy:

In January 2007, yoga therapy was defined as the “process of empowering individuals to progress toward improved health and well-being through the application of the philosophy and practice of Yoga”. Nearly 14 million Americans (6.1% of the population) say that a doctor or therapist has recommended yoga to them for their health condition. In the United Kingdom, national healthcare services promote yoga as a safe and effective way to promote physical activity, improving strength, balance, and flexibility as well as a potential benefit for people with high blood pressure, heart disease, aches and pains, depression, and stress. Yoga research in medical health literature continues to increase. Over 2000 journal articles in yoga therapy have been published online. In 2012, 274 new yoga articles were added to PubMed, with 46 results after a “systematic review” title search on the US National Library of Medicine. However, the quality and direction of evidence for yoga therapy is unclear. In one clinical review, results show psychological symptoms and disorders (anxiety, depression, and sleep), pain syndromes, autoimmune conditions (asthma, diabetes, and multiple sclerosis), immune conditions (lymphoma and breast cancer), pregnancy conditions, and weight loss are all positively affected by yoga. An overview from 2010 includes 21 systematic reviews that yield unanimous positive results for just two conditions—cardiovascular risk reduction and depression. Current research suggests that a carefully adapted set of yoga poses may reduce low-back pain and improve function. Other studies also suggest that practicing yoga (as well as other forms of regular exercise) might improve quality of life; reduce stress; lower heart rate and blood pressure; help relieve anxiety, depression, and insomnia; and improve overall physical fitness, strength, and flexibility. But some research suggests yoga may not improve asthma, and studies looking at yoga and arthritis have had mixed results.

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Yoga in Australia: Results of a national survey in 2012:

Perceived effect of yoga practice on health and medical conditions by category are shown in the table below:

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Together, stress management (15.63% of all conditions reported) and anxiety (8.25%) were more commonly being addressed by yoga practice than by back (11.84%), neck (6.69%) and shoulder (2.33%) pain and related musculoskeletal problems. Women’s health was the next largest category (8.81% of conditions) with reported improvement in pre-menstrual and menopausal symptoms and assistance during and after pregnancy, ahead of gastrointestinal (6.77%), respiratory (6.42%), and cardiovascular conditions (3.66%), with consistent improvement reported across all categories. Weight management (4.77%) was also seen to be assisted by yoga practice. Health conditions were only seen to worsen in 19 of 4,754 instances.

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Flexibility:

Regardless of your preferred type, a yoga workout provides several research-tested health benefits. The poses will improve your strength, balance and flexibility. A 2005 study at the University of Wisconsin, La Crosse, found that after eight weeks of yoga classes, participants’ flexibility increased between 13 percent and 35 percent, especially in the shoulder and trunk area. Their strength, particularly in the chest and abdominal area, also increased significantly. Additionally, the relaxation and meditation aspect of yoga has health benefits. The movements and breathing will help you reduce stress and manage such conditions as sleep problems and fatigue.

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Back pain:

Often a stress-related musculoskeletal problem, back pain seems an appropriate indication for treatment with yoga, and there is a large body of literature on the subject. In a systematic review, Chou and Huffman found only 3 studies meeting inclusion criteria on yoga’s effectiveness for subacute or chronic low back pain. One large study found 6 weeks of Viniyoga was superior to conventional exercise programs and a self-care booklet in reducing pain and “bothersomeness” scores, as well as reducing the need for analgesic medication.  Physician visits for back pain were not reduced in the treatment group, however. Also included in the systematic review were 2 smaller studies of Iyengar yoga on low back pain; results did not rise to statistical significance. A review by Posadzki and Ernst included 4 randomized controlled trials (RCTs) not included in Chou and Huffman, although only one of these had >50 subjects. Yoga practices for the treatment groups were mostly Iyengar and Viniyoga and lasted for 12 to 24 weeks, although one study used a 7-day intensive inpatient treatment program. Yoga practitioners had lower pain scores and lower Roland Morris Disability scores.  A 2004 Clinical Inquiry in The Journal of Family Practice found limited evidence to suggest yoga may speed healing for patients with chronic back pain. Most recently, Cramer et al found 12 studies meeting inclusion criteria that reported on Viniyoga, Iyengar, and Hatha yoga interventions. Ten of these studies were included in the meta-analysis, which strongly favored yoga over control interventions for reducing pain and disability scores.

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Nonpharmacologic Therapies for Acute and Chronic Low Back Pain:

A Review of the Evidence for an American Pain Society/American College of Physicians: a 2007 study:

Therapies with good evidence of moderate efficacy for chronic or subacute low back pain are cognitive-behavioral therapy, exercise, spinal manipulation, and interdisciplinary rehabilitation. For acute low back pain, the only therapy with good evidence of efficacy is superficial heat.

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Researchers find Yoga may be effective for Chronic Low Back Pain in Minority Populations: a 2009 study:

Researchers from Boston University School of Medicine (BUSM) and Boston Medical Center found that yoga may be more effective than standard treatment for reducing chronic low back pain in minority populations. This study appears in Alternative Therapies in Health and Medicine.

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A systematic review and meta-analysis of yoga for low back pain: a 2013 review:

MEDLINE, the Cochrane Library, EMBASE, CAMBASE, and PsycINFO, were screened through January 2012. Randomized controlled trials comparing yoga to control conditions in patients with low back pain were included. Two authors independently assessed risk of bias using the risk of bias tool recommended by the Cochrane Back Review Group. Main outcome measures were pain, back-specific disability, generic disability, health-related quality of life, and global improvement. For each outcome, standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated. Ten randomized controlled trials with a total of 967 chronic low back pain patients were included. Eight studies had low risk of bias. There was strong evidence for short-term effects on pain (SMD=-0.48; 95% CI, -0.65 to -0.31; P<0.01), back-specific disability (SMD=-0.59; 95% CI, -0.87 to -0.30; P<0.01), and global improvement (risk ratio=3.27; 95% CI, 1.89-5.66; P<0.01). There was strong evidence for a long-term effect on pain (SMD=-0.33; 95% CI, -0.59 to -0.07; P=0.01) and moderate evidence for a long-term effect on back-specific disability (SMD=-0.35; 95% CI, -0.55 to -0.15; P<0.01). There was no evidence for either short-term or long-term effects on health-related quality of life. Yoga was not associated with serious adverse events. This systematic review found strong evidence for short-term effectiveness and moderate evidence for long-term effectiveness of yoga for chronic low back pain in the most important patient-centered outcomes. Yoga can be recommended as an additional therapy to chronic low back pain patients.

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Depression and anxiety:

Yoga therapy for depression and anxiety has been commonly studied, given that aspects of mindfulness and relaxation are thought to be important parts of treatment. Moreover, patients uncomfortable with pharmacologic therapy for their disorders may be amenable to yoga treatment. In a recent Clinical Inquiry, Skowronek et al found evidence (strength of recommendation B) for yoga to treat depression and anxiety symptoms based on 3 recently published review articles that commented on a total of 23 RCTs. A handful of additional review papers on this subject have selected slightly different groups of studies to include in their analyses, but all have found generally positive results.  Inclusion criteria varied: one review omitted breathing-only modalities such as Sudarshan Kriya yoga, while another included them. One omitted Mindfulness-Based Stress Reduction (MBSR), which is a program developed in the United States based on several Eastern and Western methodologies including yoga.  MBSR already has a large body of literature supporting its use for anxiety and depression.  One of these reviews, which involved a meta-analysis of 9 studies regarding depression, also included a meta-analysis of 5 studies on yoga for anxiety. Pooled results for depression showed significant benefit for yoga over usual care, and smaller but still significant benefit for yoga over aerobic exercise or other relaxation techniques. For anxiety, pooled analysis showed yoga to be equal to usual care but superior to other relaxation modalities.  As with earlier reviews, study groups were heterogeneous and included young and older adults, caregivers for dementia patients, and those receiving inpatient treatment for alcohol dependency; symptoms of depression ranged from mild to severe. In a review focusing on anxiety disorders, Kirkwood et al located 8 trials, 6 of which were randomized. Many of these were published in the 1970s and 80s. The yoga interventions varied and included weekly Kundalini sessions, pranayama techniques, and savasana (a pose in which practitioners lie supine while focusing on breathing and muscle relaxation). These practices were compared with anxiolytic medication, progressive muscular relaxation, placebo capsule, and no treatment. All found a statistically significant reduction in anxiety indices in the yoga treatment groups, and the authors noted that the positive effects of yoga for those suffering from obsessive-compulsive disorders are particularly well documented.  More recently, Li and Goldsmith reviewed 6 interventional studies that included some trials without randomization, blinding, or a control group. Subjects of the studies included cancer patients, postmenopausal women, pregnant women, and firefighters. Six of 9 trials showed improvement in externally validated anxiety indices such as the State-Trait Anxiety Inventory or Perceived Stress Scale.

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A 2010 review evaluated eight trials based on individuals with clinical depression and elevated depression symptoms. Benefits were found in relation to mindfulness, physical activity, decreased stress reactivity, sleep regulation, decreased rumination, regulating neurotransmitters, promotion of adaptive thinking, and promotion of behavioural activation. A type of controlled breathing with roots in traditional yoga shows promise in providing relief for depression. The program, called Sudarshan Kriya yoga (SKY), involves several types of cyclical breathing patterns, ranging from slow and calming to rapid and stimulating. One study compared 30 minutes of SKY breathing, done six days a week, to bilateral electroconvulsive therapy and the tricyclic antidepressant imipramine in 45 people hospitalized for depression. After four weeks of treatment, 93% of those receiving electroconvulsive therapy, 73% of those taking imipramine, and 67% of those using the breathing technique had achieved remission. Another study examined the effects of SKY on depressive symptoms in 60 alcohol-dependent men. After a week of a standard detoxification program at a mental health center in Bangalore, India, participants were randomly assigned to two weeks of SKY or a standard alcoholism treatment control. After the full three weeks, scores on a standard depression inventory dropped 75% in the SKY group, as compared with 60% in the standard treatment group. Levels of two stress hormones, cortisol and corticotropin, also dropped in the SKY group, but not in the control group. The authors suggest that SKY might be a beneficial treatment for depression in the early stages of recovery from alcoholism. And a 2007 study supports yoga’s potential as a complementary treatment for depressed patients taking antidepressant medication but only in partial remission. University of California, Los Angeles, psychologist David Shapiro, PhD, found that participants who practiced Iyengar yoga three times a week for eight weeks reported significant reductions in depression, anxiety and neurotic symptoms, as well as mood improvements at the end of each class (Evidence-based Complementary and Alternative Medicine, Vol. 4, No. 4). Many of the participants achieved remission and also showed physiological changes, such as heart rate variability, indicative of a greater capacity for emotional regulation, Shapiro says.

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Yoga for depression:  systemic review 2005:

Searches of the major biomedical databases including MEDLINE, EMBASE,  ClNAHL, PsycINFO and the Cochrane Library were conducted. Specialist  complementary and alternative medicine (CAM) and the IndMED databases were also searched and efforts made to identify unpublished and ongoing research.  Searches were conducted between January and June 2004. Relevant research was categorised by study type and appraised. Clinical commentaries were obtained for studies reporting clinical outcomes.  Five randomised controlled trials were located, each of which utilised different forms of yoga interventions and in which the severity of the condition ranged from mild to severe. All trials reported positive findings but methodological details such as method of randomisation, compliance and attrition rates were missing. No adverse effects were reported with the exception of fatigue and breathlessness in participants in one study.  Overall, the initial indications are of potentially beneficial effects of yoga interventions on depressive disorders. Variation in interventions, severity and reporting of trial methodology suggests that the findings must be interpreted with caution. Several of the interventions may not be feasible in those with reduced or impaired mobility. Nevertheless, further investigation of yoga as a therapeutic intervention is warranted.

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Here are five poses that can specifically help with depression:

1. Forward fold (Uttanasana).

2. Head-to-Knee Forward Bend (Janu Sirsasana).

3. Cobra (Bhujangasana).

4. Bridge (Setu Bandha Sarvangasana)

5. Supported Headstand (Salamba Sirsasana).

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Yoga for anxiety: a systematic review of the research evidence: year 2005:

Between March and June 2004, a systematic review was carried out of the research evidence on the effectiveness of yoga for the treatment of anxiety and anxiety disorders. Eight studies were reviewed. They reported positive results, although there were many methodological inadequacies. Owing to the diversity of conditions treated and poor quality of most of the studies, it is not possible to say that yoga is effective in treating anxiety or anxiety disorders in general. However, there are encouraging results, particularly with obsessive compulsive disorder. Further well conducted research is necessary which may be most productive if focused on specific anxiety disorders.

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Effects of Yoga versus Walking on Mood, Anxiety, and Brain GABA Levels:

A Randomized Controlled MRS Study of 2010:

Yoga and exercise have beneficial effects on mood and anxiety. γ-Aminobutyric acid (GABA)-ergic activity is reduced in mood and anxiety disorders. The practice of yoga postures is associated with increased brain GABA levels. This study addresses the question of whether changes in mood, anxiety, and GABA levels are specific to yoga or related to physical activity. Healthy subjects with no significant medical/psychiatric disorders were randomized to yoga or a metabolically matched walking intervention for 60 minutes 3 times a week for 12 weeks. Mood and anxiety scales were taken at weeks 0, 4, 8, 12, and before each magnetic resonance spectroscopy (MRS) scan. Scan 1 was at baseline. Scan 2, obtained after the 12-week intervention, was followed by a 60-minute yoga or walking intervention, which was immediately followed by Scan 3. The yoga subjects (n = 19) reported greater improvement in mood and greater decreases in anxiety than the walking group (n = 15). There were positive correlations between improved mood and decreased anxiety and thalamic GABA levels. The yoga group had positive correlations between changes in mood scales and changes in GABA levels. The 12-week yoga intervention was associated with greater improvements in mood and anxiety than a metabolically matched walking exercise. This is the first study to demonstrate that increased thalamic GABA levels are associated with improved mood and decreased anxiety. It is also the first time that a behavioral intervention (i.e., yoga postures) has been associated with a positive correlation between acute increases in thalamic GABA levels and improvements in mood and anxiety scales. Given that pharmacologic agents that increase the activity of the GABA system are prescribed to improve mood and decrease anxiety, the reported correlations are in the expected direction. The possible role of GABA in mediating the beneficial effects of yoga on mood and anxiety warrants further study.

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Mood and functioning:

In a German study published in 2005, women who described themselves as “emotionally distressed” are treated with 90-min yoga classes a week for 3 months. At the end of 3 months, women in the yoga group reported improvements in perceived stress, depression, anxiety, energy, fatigue, and well-being. Depression scores improved by 50%, anxiety scores 30%, and overall well-being scores by 65%. Initial complaints of headaches, back pain, and poor sleep quality also resolved much more often in the yoga group than in the control group. Another 2005 study examined the effects of a single yoga class for inpatients at the New Hampshire psychiatric hospital, 113 participants among patients with bipolar disorder, major depression, and schizophrenia it is found after yoga class, tension, anxiety, depression, anger, hostility, and fatigue dropped significantly. Further controlled trials of yoga practice have demonstrated improvements in mood and quality of life for elderly, people caring for patients with dementia, breast cancer survivors, and patients with epilepsy.

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Using Yoga to relieve Stress:

Yoga-based guided relaxation reduces sympathetic activity judged from baseline levels.

35 male volunteers whose ages ranged from 20 to 46 years were studied in two sessions of yoga-based guided relaxation and supine rest. Assessments of autonomic variables were made for 15 subjects, before, during, and after the practices, whereas oxygen consumption and breath volume were recorded for 25 subjects before and after both types of relaxation. A significant decrease in oxygen consumption and increase in breath volume were recorded after guided relaxation (paired test). There were comparable reductions in heart rate and skin conductance during both types of relaxation. During guided relaxation the power of the low frequency component of the heart-rate variability spectrum reduced, whereas the power of the high frequency component increased, suggesting reduced sympathetic activity. Also, subjects with a baseline ratio of LF/HF > 0.5 showed a significant decrease in the ratio after guided relaxation, while subjects with a ratio < or = 0.5 at baseline showed no such change. The results suggest that sympathetic activity decreased after guided relaxation based on yoga, depending on the baseline levels.

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Yoga and cortisol: a 2011 study:

Cohen and his colleagues found that while simple stretching exercises counteracted fatigue, patients who participated in yoga exercises that incorporated controlled breathing, meditation and relaxation techniques experienced improved ability to engage in their daily activities, better general health and better regulation of the stress hormone cortisol. To conduct the study, 191 women with breast cancer (stage 0-3) were randomized to one of three groups: 1) yoga; 2) simple stretching; or 3) no instruction in yoga or stretching. Participants in the yoga and stretching groups attended sessions specifically tailored to breast cancer patients for one-hour, three days a week throughout their six weeks of radiation treatment. Women who practiced yoga had the steepest decline in their cortisol levels across the day, indicating that yoga had the ability to help regulate this stress hormone. According to Cohen this is particularly important because higher stress hormone levels throughout the day—known as a blunted circadian cortisol rhythm—have been linked to worse breast cancer outcomes. Although these findings focused on patients with cancer, it is likely that the cortisol regulating benefits of yoga are universal.

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Yoga and post-traumatic stress disorder (PTSD):

Psychologists are also examining the use of yoga with survivors of trauma and finding it may even be more effective than some psychotherapy techniques. In a pilot study at the Trauma Center at the Justice Resource Institute in Brookline, Mass., women with PTSD who took part in eight sessions of a 75-minute Hatha yoga class experienced significantly reduced PTSD symptoms compared with those participating in a dialectical behavior therapy group. The center recently received a grant from the National Center for Complementary and Alternative Medicine to conduct a randomized, single-blind, controlled study to further examine whether, as compared with a 10-week health class, yoga improves the frequency and severity of PTSD symptoms and other somatic complaints as well as social and occupational impairments among female trauma survivors.

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Yoga and insomnia:

Pharmacological treatment of insomnia is often associated with hazardous side effects such as states of confusion, psychomotor performance deficits, nocturnal falls, dysphoric mood, impaired intellectual functioning and daytime sleepiness, especially in older adults. Therefore, alternative forms of therapy for improving sleep are becoming utilized more frequently. These alternative therapeutic approaches can be generally classified into three categories: behavioral based educative methods (e.g. avoiding caffeine or other stimulants before bedtime), relaxation techniques (e.g. progressive muscular relaxation, yoga, and meditation) and formal psychotherapy. Because of its ability to increase relaxation and induce a balanced mental state, yoga has been studied to evaluate its possible effects on sleep and insomnia.  An as-yet-unpublished randomized control trial by Khalsa offers insight into how yoga may reduce insomnia. In this study, 20 participants who practiced a daily 45-minute series of Kundalini yoga techniques shortly before bedtime for eight weeks reported significant reductions in insomnia severity as compared with those told to follow six behavioral recommendations for sleep hygiene.

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Yoga in schizophrenia: a systematic review of randomised controlled trials. Year 2012:

The objective of this systematic review was to assess the effectiveness of yoga as a complementary treatment on general psychopathology, positive and negative symptoms and health-related quality of life (HRQL) for people with schizophrenia. Only three RCTs met the inclusion criteria. Lower Positive and Negative Syndrome Scale (PANSS) total scores and subscale scores for positive and negative symptoms were obtained after yoga compared with exercise or waiting list control conditions. In the same way, the physical, psychological, social and environmental HRQL as measured with the abbreviated version of the World Health Organization Quality of Life questionnaire (WHOQOL-BREF) increased more significantly after yoga than after exercise or waiting list control conditions. None of the RCTS encountered adverse events. Dose-response relationships could, however, not be determined. Although the number of RCTs included in this review was limited, results indicated that yoga therapy can be an useful add-on treatment to reduce general psychopathology and positive and negative symptoms. In the same way, HRQL improved in those antipsychotic-stabilised patients with schizophrenia following yoga.

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Asthma and COPD:

Yoga and lungs:

Madanmohan et al. have reported that 12 weeks of yoga practice results in a significant increase in maximum expiratory pressure, maximum inspiratory pressure, breath holding time after expiration, breath holding time after inspiration, and hand grip strength.  Joshi et al. have also demonstrated that 6 weeks of pranayama breathing course resulted in improved ventilatory functions in the form of lowered respiratory rate, and increases in the forced vital capacity, forced expiratory volume at the end of first second, maximum voluntary ventilation, peak expiratory flow rate, and prolongation of breath holding time. Similar beneficial effects were observed by Makwana et al. after 10 weeks of yoga practice. An increase in inspiratory and expiratory pressures suggests that yoga training improves the strength of expiratory and as well as inspiratory muscles. Respiratory muscles are like skeletal muscles. Yogic techniques involve isometric contraction which is known to increase skeletal muscle strength. Breath holding time depends on initial lung volume. Greater lung volume decreases the frequency and amplitude of involuntary contractions of respiratory muscles, thereby lessening the discomfort of breath holding. During yoga practice, one consistently and consciously over-rides the stimuli to respiratory centers, thus acquiring control over the respiration. This, along with improved cardio-respiratory performance, may explain the prolongation of breath holding time in yoga-trained subjects.

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Asthma:

With its focus on awareness of breath and the mechanics of breathing, yoga would seem a natural adjunct to conventional asthma therapy. One systematic review found 4 trials (3 RCTs) that showed statistically significant improvements in spirometric measurements in patients with asthma who practiced yoga techniques. An additional 3 RCTs showed no improvements with yoga over conventional treatments.  Overall, the reviewers noted that study quality was poor, although they said several studies were appropriately designed. Again, the interventions described as “yoga” varied considerably, from Iyengar type classes to meditation-focused techniques to pranayama exercises. Follow-up ranged from 6 weeks to 6 months. A more recent and thorough review found 14 RCTs using yoga to treat asthma symptoms. The investigators performed pooled analysis despite significant heterogeneity in the studies. The analysis showed some improvement in the yoga group compared with usual therapy, but no difference in comparison with sham yoga or non-yoga breathing exercises.

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Yoga for asthma: a systematic review and meta-analysis, 2014:

MEDLINE/PubMed, Scopus, the Cochrane Central Register of Controlled Trials, PsycINFO, CAM-Quest, CAMbase, and IndMED were searched through January 2014. Randomized controlled trials of yoga for patients with asthma were included if they assessed asthma control, symptoms, quality of life, and/or pulmonary function. For each outcome, standardized mean differences (SMDs) or risk ratios (RRs) and 95% confidence intervals (CIs) were calculated. Risk of bias was assessed using the Cochrane tool. Fourteen randomized controlled trials with 824 patients were included. Evidence for effects of yoga compared with usual care was found for asthma control (RR, 10.64; 95% CI, 1.98 to 57.19; P = .006), asthma symptoms (SMD, -0.37; 95% CI, -0.55 to -0.19; P < .001), quality of life (SMD, 0.86; 95% CI, 0.39 to 1.33; P < .001), peak expiratory flow rate (SMD, 0.49; 95% CI, 0.32 to 0.67; P < .001), and ratio of forced expiratory volume in 1 second to forced vital capacity (SMD, 0.50; 95% CI, 0.24 to 0.75; P < .001); evidence for effects of yoga compared with psychological interventions was found for quality of life (SMD, 0.61; 95% CI, 0.22 to 0.99; P = .002) and peak expiratory flow rate (SMD, 2.87; 95% CI, 0.14 to 5.60; P = .04). No evidence for effects of yoga compared with sham yoga or breathing exercises was revealed. No effect was robust against all potential sources of bias. Yoga was not associated with serious adverse events. Yoga cannot be considered a routine intervention for asthmatic patients at this point. It can be considered an ancillary intervention or an alternative to breathing exercises for asthma patients interested in complementary interventions.

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An Integrated Approach of Yoga Therapy for Bronchial Asthma: A 3–54-Month Prospective Study: 2015:

After an initial integrated yoga training program of 2 to 4 weeks, 570 bronchial asthmatics were followed up for 3 to 54 months. The training consisted of yoga practices—yogasanas, Prānāyāma, meditation, and kriyas—and theory of yoga. Results show highly significant improvement in most of the specific parameters. The regular practitioners showed the greatest improvement. Peak expiratory flow rate (PFR) values showed significant movement of patients toward normalcy after yoga, and 72, 69, and 66% of the patients have stopped or reduced par-enteral, oral, and cortisone medication, respectively. These results establish the long-term efficacy of the integrated approach of yoga therapy in the management of bronchial asthma.

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Yoga Therapy decreases Dyspnea-Related Distress and improves Functional Performance in people with Chronic Obstructive Pulmonary Disease (COPD): A Pilot Study:

The primary purpose of this pilot study was to evaluate a yoga program for its safety, feasibility, and efficacy for decreasing dyspnea intensity (DI) and dyspnea-related distress (DD) in older adults with COPD. The major findings of this pilot study were that this 12-week yoga program was safe, feasible, and enjoyable for older adults with COPD. In addition, patients who participated in the program improved their exercise performance and self-reported functional performance and decreased their DD more than subjects who received educational pamphlets on COPD. Although the minimal clinically important difference (MCID) has not yet been established for DD measured on the modified Borg scale, the MCID for DI is one point. Using this criterion as a proxy, the improvement in DD experienced after participation in the yoga intervention would be considered clinically significant. DI and pulmonary function did not change; however, the ability of these patients to walk longer without feeling as bothered by dyspnea may indicate an improvement in their perceived ability to control their dyspnea during exercise. This was a pilot feasibility study, not specifically powered to detect changes even in the primary outcome of dyspnea. Therefore, it must be acknowledged that these positive findings may be due to chance, given the small sample, the multiple comparisons, and very modest changes in the secondary outcomes.

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Hypertension:

It is well known that many antihypertensive agents have been associated with numerous undesirable side effects. In addition to medication, moderately intense aerobic exercise is well known to lower blood pressure. Yoga, together with relaxation, biofeedback, transcendental meditation, and psychotherapy, has been found to have a convincing antihypertensive effect. The mechanism of yoga-induced blood pressure reduction may be attributed to its beneficial effects on the autonomic neurological function. Impaired baroreflex sensitivity has been increasingly postulated to be one of the major causative factors of essential hypertension. The practice of yogic postures has been shown to restore baroreflex sensitivity. Yogic asanas that are equivalent to head-up or head-down tilt were discovered to be particularly beneficial in this regard. Tests proved a progressive attenuation of sympatho-adrenal and renin-angiotensin activity with yogic practice. Yogic practice, through the restoration of baroreceptor sensitivity, caused a significant reduction in the blood pressure of patients who participated in yoga exercise. Yoga has proven efficacy in managing secondary cardiac complications due to chronic hypertension. Left ventricular hypertrophy secondary to chronic hypertension is a harbinger of many chronic cardiac complications, such as myocardial ischemia, congestive cardiac failure, and impairment of diastolic function. Cardiovascular response to head-down-body-up postural exercise (Sarvangasana) has been shown to be particularly beneficial in preventing and treating hypertension-associated left ventricular hypertrophy and diastolic dysfunction. In one study, the practice of sarvangasana for 2 weeks caused resting heart rate and left ventricular end diastolic volume to reduce significantly. In addition, there was mild regression of left ventricular mass as recorded in echocardiography. One can always rely on B.K.S. Iyengar for straightforward guidance on asanas to support our physical health. In Light on Yoga he contends that Halasana (Plow Pose), Janu Sirsasana (Head to Knee Pose), Paschimottanasana (Seated Forward Fold), Virasana (Hero’s Pose) and Savasana (Corpse Pose) aid in lowering high blood pressure because the poses are calming in nature. These poses would be of particular help to those with stress related blood pressure issues. Additionally, restorative inversions like Viparita Karani (Legs Up the Wall Pose) use gravity to bring blood flow from feet back down to the torso. This has a nourishing effect on the central nervous system and gives the heart a “blood flow break” for the duration of the pose. If possible, holding this pose for 10-20 minutes is recommended to receive the full benefits, but better to practice it for less time than not at all. Regular practice of this pose, as simple as it may seem, can have notable effects on your stress levels and overall bodily balance. Interestingly enough, Iyengar recommends some of the same poses—Halasana, Paschimottonasana, and Virasana—for those with low blood pressure. This is because these poses calm and regulate the nervous system bringing the body into balance in whatever way it needs. Poses like Salamba Sirsasana (Headstand) and Salamba Sarvangasana (Shoulder Stand) are a bit more stimulating to the system (think: blood and energy flow to the brain) and therefore recommended more for raising blood pressure than lowering it. When it comes to pranayama (breath control), simple breathing practices are available for those with high or low blood pressure. An easy one to try is Nadi Sodhana, or alternate nostril breathing. Note that however you may have been instructed with this breath in the past, it is important for those with blood pressure issues (and those newer to pranayama) to not hold the breath at the top of the inhale. Retentions of the breath are best practiced after building a strong foundational understanding of the bandhas, and not necessarily of utmost importance when aiming to regulate blood pressure. Meditation and relaxation techniques can also be effective in balancing your blood pressure. Research conducted by the National Institute of Health has shown that people who meditate regularly experience a significant reduction in blood pressure, with nearly 50% showing lower rates of heart attack, stroke and mortality. Though meditation is a simple practice (all one needs is a place to sit), it has proven time and time again to enhance health and happiness.

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Yoga is often said to reduce blood pressure (BP), which would make sense given the emphasis put on relaxation by many schools of yoga. In the past few years, 3 review articles have been published, as well as 2 relevant RCTs not included in those reviews. Hagins et al found 17 RCTs using yoga to treat adults with hypertension and prehypertension. These included both blinded and unblinded studies, and yoga interventions were compared with usual treatment, education, or non-yoga exercise. The authors included only studies of asanas intervention, and excluded interventions using only breathing or relaxation techniques. In meta-analysis, pooled data showed the yoga treatment decreased both diastolic BP (DBP) and systolic BP (SBP) by 3 to 4 mm Hg compared with usual treatment, but not when compared with other exercise therapies.  Reviewers concluded that yoga was likely as effective for lowering BP as other types of physical activity. In a review without meta-analysis, Posadzki et al also found 17 blinded RCTs using yoga to treat hypertension or prehypertension in adults. Eleven of the 17 studies favoured yoga, with 8 showing a decrease in SBP and 5 in DBP. All but 2 studies were found to be of poor quality, especially with regard to blinding. The authors noted that studies using subjects with prehypertension or hypertension with comorbidities were more likely to show significant results, speculating that yoga may be more effective for these populations. In an ambitious review article on yoga as treatment for a variety of risk factors for cardiovascular disease, Cramer et al located 28 RCTs that addressed effects of yoga on BP. Seven of the studies in the Posadzki review were included. Meta-analysis showed a statistically significant decrease in SBP of 5.85 mm Hg and in DBP of 4.12 mm Hg. Although wide in scope, this meta-analysis included many studies of healthy patients without hypertension who could conceivably have differing neuroendocrine responses to yoga practice. In a pilot RCT, Cohen et al found a significant decrease in BP among subjects randomized into Iyengar yoga classes for 24 weeks compared with a control group educated about lifestyle modification.  These studies were unique in that no subjects were currently being treated with antihypertensive medications; most other trials on this subject enrolled participants on antihypertensive medications if their regimens had been stable for some time. In an RCT published recently by Hagins et al, subjects with pre- or stage I hypertension were randomized into Ashtanga yoga classes or non-aerobic exercise classes formulated to burn equivalent METs. After 12 weeks of treatment, the yoga subjects’ BP had significantly decreased from starting values, but was not improved compared with the exercise subjects. This further supports the assertion that yoga is equivalent to other forms of physical activity in decreasing BP among hypertensive subjects.

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Yoga for Essential Hypertension: A Cochrane Systematic Review 2103:

MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library were searched until June, 2013. Authors included randomized clinical trials testing yoga against conventional therapy, yoga versus no treatment, yoga combined with conventional therapy versus conventional therapy or conventional therapy combined with breath awareness. Study selection, data extraction, quality assessment, and data analyses were conducted according to the Cochrane standards. A total of 6 studies (involving 386 patients) were included. The methodological quality of the included trials was evaluated as generally low. A total of 6 RCTs met all the inclusion criteria. 4 of them compared yoga plus conventional therapy with conventional therapy. 1 RCT described yoga combined with conventional therapy versus conventional therapy combined with breath awareness. 2 RCT tested the effect of yoga versus conventional therapy alone. 1 RCT described yoga compared to no treatment. Only one trial reported adverse events without details, the safety of yoga is still uncertain. There is some encouraging evidence of yoga for lowering SBP and DBP. However, due to low methodological quality of these identified trials, a definite conclusion about the efficacy and safety of yoga on hypertension cannot be drawn from this review. Therefore, further thorough investigation, large-scale, proper study designed, randomized trials of yoga for hypertension will be required to justify the effects reported here.

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Balance and stability in the elderly:

With its emphasis on strength, balance, and body awareness, yoga would seem a helpful intervention for older patients at risk of injury from falls. Unfortunately this area of research lacks significant numbers of controlled trails. In a Cochrane review of exercise interventions for improving balance in the elderly, the reviewers were unable find any studies specifically using yoga that met their criteria. Jeter et al  attempted a review more recently, and found 15 studies meeting inclusion criteria, 5 of which were RCTs. Overall, however, the poor quality of the studies and variation in both the type of yoga used as intervention and measurements of balance precluded pooled analysis, although some studies did have positive results. A small but well-designed pilot RCT was recently published showing that an Iyengar yoga intervention significantly improved timed one-leg balancing among community dwelling older adults. However, this study did not show a significant difference in a standardized fall risk survey after the intervention.  Cautioning against yoga in this context are several articles chronicling increased risks of some yoga exercises, especially for those with osteoporosis or other risks for fractures.  At this point, the well-documented risks of yoga practice in this group probably outweigh the unsubstantiated rewards.

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Exercise for improving balance in older people: Cochrane review 2012:

This updated review includes 94 (62 new to this update) randomised controlled trials involving 9821 participants. Most participants were women living in their own home. Some studies included frail people residing in hospital or residential facilities. 3D (3 dimensional) exercise include Tai Chi, qi gong, dance, yoga for which there were15 studies out of which seven provided data for one or more primary outcome. Positive effects were found for the Timed Up & Go Test; standing on one leg for as long as possible with eyes open, and with eyes closed; and the Berg Balance Scale.  Authors concluded that there is weak evidence that some types of exercise (gait, balance, co-ordination and functional tasks; strengthening exercise; 3D exercise and multiple exercise types) are moderately effective, immediately post intervention, in improving clinical balance outcomes in older people. Such interventions are probably safe.

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Yoga and diabetes:

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Various yoga practices for treatment of type 2 DM:

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Purported studies of yoga on diabetes:

Studies have also confirmed that practising certain asanas such as Ardha Matsyendrasana (half-twist pose) combined with Dhanurasana (bow pose), Vakrasana (twisted pose), Matsyendrasana (half-spinal twist), Halasana (plough pose) squeezes and compresses the abdomen and helps stimulate the pancreatic secretions or hormonal secretions. As a result, more insulin is pushed into the system. This rejuvenates the insulin producing beta cells in the pancreas of diabetics suffering from both type 1 and 2. Practising the postures in a relaxed manner, without exertion, meditation and breathing techniques help most patients control the triggers or causes of diabetes. A study, by S A Ramaiah in Washington, compared the effects of exercise such as walking, jogging on a treadmill, static cycling with asanas such as Upavishta Bakasana (sitting crane), Bakasana (standing crane) and Dhanurasana. It was found that these asanas were the most effective as they helped stimulate the hormonal secretion of the pancreas and rejuvenate its capacity to produce insulin. They also strengthened the back muscles which enhance toning of abdominal viscera (muscles and internal organs).The balancing in Bakasana improves interaction between the pituitary gland and pancreas. Aside from asanas, breathing exercises especially anulom vilom (alternate nostril breathing) and kapalbatti (one-time inhale; exhale 30 to 50 times quickly) is extremely beneficial. Anulom vilom is found useful in diabetes as alternate nostril breathing has calming effects on the nervous system, facilitating homeostasis (internal equilibrium in the function of all the systems). This manages the stress levels, helping in diabetes treatment. Kapalbhatti, on the other hand, stimulates the pancreas to release insulin, thus helping control diabetes. Pranayam makes the mind calm, thus balancing the interaction between the pituitary gland and the pancreas. Kapalabhati combined with Nauli Kriya (pressure manipulations and isolation of abdominal-recti muscles) help control blood sugar. These practices balance the Basic Metabolic Rate (BMR) which in turn helps stabilise sugar levels.  Once you are through with the practice, relax in shavasana (lying flat on the ground) to cool off. A yogic diet that is high in fibre, whole grains, legumes and vegetables complements the regimen. It is recommended to lose excess weight and stabilise blood sugar levels.

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The beneficial effect of yoga in diabetes, a 2005 study:

Twenty NIDDM subjects (mild to moderate diabetics) in the age group of 30-60 years were selected from the outpatient clinic of G.T.B. hospital. They were on a 40 days yoga asana regime under the supervision of a yoga expert. 13 specific Yoga asanas < or = done by Type 2 Diabetes Patients included. Surya Namaskar, Trikonasana, Tadasana, Sukhasana, Padmasana, Bhastrika Pranayama, Pashimottanasana, Ardhmatsyendrasana, Pawanmuktasana, Bhujangasana, Vajrasana, Dhanurasana and Shavasana are beneficial for diabetes mellitus. Serum insulin, plasma fasting and one hour postprandial blood glucose levels and anthropometric parameters were measured before and after yoga asanas. The results indicate that there was significant decrease in fasting glucose levels from basal 208.3 +/- 20.0 to 171.7 +/- 19.5 mg/dl and one hour postprandial blood glucose levels decreased from 295.3 +/- 22.0 to 269.7 +/- 19.9 mg/dl. The exact mechanism as to how these postures and controlled breathing interact with somatoendocrine mechanism affecting insulin kinetics was worked out. A significant decrease in waist-hip ratio and changes in insulin levels were also observed, suggesting a positive effect of yoga asanas on glucose utilisation and fat redistribution in NIDDM. Yoga asanas may be used as an adjunct with diet and drugs in the management of Type 2 diabetes.

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A 2007 review looked at 25 studies that evaluated the metabolic and clinical effects of yoga in adults with diabetes mellitus type 2. Beneficial changes were found in several areas including glucose tolerance and insulin sensitivity, lipid profiles, blood pressure, oxidative stress, coagulation profiles, pulmonary function and specific clinical outcomes.

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Effect of 3-Month Yoga on Oxidative Stress in Type 2 Diabetes With or Without Complications: a 2011 study:

The study involved 123 patients stratified according to groups with microvascular complications, macrovascular complications, and peripheral neuropathy and without complications and assigned to receive either standard care or standard care along with additional yoga for 3 months. In comparison with standard care alone, yoga resulted in significant reduction in BMI, glycemic control, and malondialdehyde and increase in glutathione and vitamin C. There were no differences in waist circumference, waist-to-hip ratio, blood pressure, vitamin E, or superoxide dismutase in the yoga group at follow-up. Yoga can be used as an effective therapy in reducing oxidative stress in type 2 diabetes. Yoga in addition to standard care helps reduce BMI and improve glycemic control in type 2 diabetic patients.  Oxidative stress has been implicated as the root cause underlying the development of insulin resistance, β-cell dysfunction, diabetes, and its associated clinical conditions such as atherosclerosis, microvascular complications, and neuropathy. Yoga has been found to be beneficial in reducing oxidative stress in type 2 diabetes, but there is a lack of controlled trials to demonstrate the same. This report describes the effect of yoga on oxidative stress, glycemic control, blood pressure control, and anthropometry in type 2 diabetic patients with or without complications compared with control subjects on standard care.

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Speeds Nerve Impulses:

One of the major problems from long term diabetes is nerve damage due to constant high sugar levels in the body. This nerve damage leads to the slowing of nerve impulses, decreased sensation, numbness of the feet, and poor bowel function. Can yoga help? Scientists at Guru Tegh Bahadur Hospital, in Delhi, India, studied a group of 20 type 2 diabetic subjects between the ages of 30-60 years. Their aim was to see whether Yoga asanas had any effect on nerve conduction. TheYoga asanas included Suryanamskar Tadasan, Konasan, Padmasan Pranayam, Shavasan, Pavanmukthasan, Sarpasan and Shavasan. The Yoga exercises were performed for 40 minutes every day for 40 days in the above sequence. The subjects continued their normally prescribed medicines and diet. Blood sugar and nerve conduction velocity of the median nerve (in the hand) were measured and repeated after 40 days of the Yogic regime. Another group of 20 type 2 diabetes subjects of comparable age and severity, called the control group, were kept on prescribed medication and light physical exercises like walking. Their initial & post 40 days parameters were recorded for comparison. At the end of the 40 days, those who did the yoga had improved the nerve impulse in their hands. The hand nerve conduction velocity increased from 52.8 meters per second to 53.8 m/sec. The control group nerve function deteriorated over the period of study, indicating that diabetes is a slowly progressive disease involving the nerves. The authors conclude that Yoga asanas have a beneficial effect on blood sugar control and improve nerve function in type 2 diabetics who have mild nerve damage.

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Yoga Practice for the Management of Type II Diabetes Mellitus in Adults: A systematic review 2007:

The effect of practicing yoga for the management of type II Diabetes was assessed in this systematic review through searching related electronic databases and the grey literature to the end of May 2007 using Ovid. All randomized controlled clinical trials (RCTs) comparing yoga practice with other type of intervention or with regular practice or both, were included regardless of language or type of publication. Each study was assessed for quality by two independent reviewers. Mean difference was used for summarizing the effect of each study outcomes with 95% confidence intervals. Pooling of the studies did not take place due to the wide clinical variation between the studies. Publication bias was assessed by statistical methods. Five trials with 363 participants met the inclusion criteria with medium to high risk of bias and different intervention characteristics. The studies’ results show improvement in outcomes among patients with diabetes type II. These improvements were mainly among short term or immediate diabetes outcomes and not all were statistically significant. The results were inconclusive and not significant for the long-term outcomes. No adverse effects were reported in any of the included studies. Short-term benefits for patients with diabetes may be achieved from practicing yoga. Further research is needed in this area. Factors like quality of the trials and other methodological issues should be improved by large randomized control trials with allocation concealment to assess the effectiveness of yoga on diabetes type II. A definitive recommendation for physicians to encourage their patients to practice yoga cannot be reached at present.

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My view:

Type II diabetes mellitus (T2DM) is the commonest type of diabetes. The first indicator of T2DM is increased post-prandial plasma glucose more than 140 mgs per 100 ml blood. Fasting plasma glucose rises later. However, by the time PPPG rises to detect T2DM, 50 % of the insulin producing pancreatic beta cells are already dead.  It is impossible for any yoga or any exercise that would stimulate pancreas to rejuvenate dead cells. Diet modification and physical exercise do help by reducing glucose load on pancreas and by increasing insulin sensitivity thereby control hyperglycaemia. Yoga diet is a vegetarian diet with most food items having low glycaemic index reducing glucose load on pancreas and yoga asanas are isometric exercise increasing insulin sensitivity. Therefore yoga does help in diabetic control by yoga diet and yoga exercise akin to traditional diet control and physical exercise.

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Yoga and heart:

The debate rages on about yoga and cardiovascular health, and while there is no clear answer, it is possible that yoga has no effect in this area. In fact, that CSU study showed no change in aerobic or cardiovascular fitness whatsoever. Aerobic activity, however, has known cardio benefits. Such exercise broadens blood vessels for increased oxygen and nutrient delivery. It also strengthens your heart, improving efficiency. What’s more, aerobic exercise lowers “bad” LDL cholesterol levels while raising “good” HDL cholesterol, resulting in less plaque to clog up your arteries. A recent review of yoga and cardiovascular disease published in the European Journal of Preventive Cardiology indicates that yoga may help lower heart disease risk as much as conventional exercise, such as brisk walking. The studies in the review looked at different types of yoga, including both gentler and more energetic forms. The participants ranged from young, healthy individuals to older people with health conditions. Over all, people who took yoga classes saw improvements in a number of factors that affect heart disease risk. They lost an average of five pounds, shaved five points off their blood pressure, and lowered their levels of harmful LDL cholesterol by 12 points. Performing a variety of yoga postures gently stretches and exercises muscles. This helps them become more sensitive to insulin, which is important for controlling blood sugar. Deep breathing can help lower blood pressure. Mind-calming meditation, another key part of yoga, quiets the nervous system and eases stress. All of these improvements may help prevent heart disease, and can definitely help people with cardiovascular problems. Two other ancient practices that join slow, flowing motions with deep breathing — tai chi and qigong — seem to offer similar advantages.  Because yoga is less strenuous than many other types of exercise and is easy to modify, it’s perfect for people who might otherwise be wary of exercise. It can be a good addition to cardiac rehabilitation, which can help people recover from a heart attack or heart surgery.

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In a randomized controlled study, patients with angiographically proven coronary artery disease who practiced yoga exercise for a period of 1 year showed a decrease in the number of anginal episodes per week, improved exercise capacity and decrease in body weight. Serum cholesterol levels (total cholesterol, LDL cholesterol and triglyceride levels) also showed greater reductions as compared with control groups. It is evident in recent studies that yoga can control LDL cholesterol and hypertension. Revascularization procedures were required less frequently in the yoga group. Follow-up angiography at 1 year showed that significantly more lesions regressed in the yoga group compared with the control group. Thus, yoga exercise increases regression and retards progression of atherosclerosis in patients with severe coronary artery disease. However, the mechanism of this effect of yoga on the atherosclerotic plaque remains to be studied. A modified form of yoga focusing on cardiac patients, yoga for heart disease reduces heart rate and blood pressure in addition to calming the nervous system. It also increases exercise capacity and lowers inflammation levels, as shown by an ever-growing number of research studies. Patients use mats, pillows and chairs to ensure comfort while they perform yoga’s gentle exercises; although it may sound like barely enough motion to break a sweat, the positive effects of cardiovascular yoga are measurable. Eight weeks of yoga helped to safely improve overall quality of life in 19 heart failure patients, even reducing markers of inflammation associated with heart failure, according to a November 2007 study by researchers at the Emory University School of Medicine in Atlanta. Meanwhile adults with metabolic syndrome, a cluster of conditions that significantly raises cardiovascular risk, were able to reduce their waist circumference, blood pressure, blood sugar and triglycerides after practicing yoga for just three months (Diabetes Research and Clinical Practice 12/07).

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Yoga for the primary prevention of cardiovascular disease: Cochrane review 2014:

Cardiovascular disease (CVD) is a global health burden. Nevertheless, it is thought that the risk of CVD can be lowered by changing a number of risk factors, such as by increasing physical activity and using relaxation to reduce stress, both of which are components of yoga. This review assessed the effectiveness of any type of yoga in healthy adults and those at high risk of CVD. Authors found 11 trials (800 participants), none of them were large enough or of long enough duration to examine the effects of yoga on decreasing death or non-fatal endpoints. There were variations in the style and duration of yoga and the follow-up of the interventions ranged from three to eight months. The results showed that yoga has favourable effects on diastolic blood pressure, high-density lipoprotein (HDL) cholesterol and triglycerides (a blood lipid), and uncertain effects on low-density lipoprotein (LDL) cholesterol. None of the included trials reported adverse events, the occurrence of type 2 diabetes or costs. Longer-term, high-quality trials are needed in order to determine the effectiveness of yoga for CVD prevention.

Quality of the Evidence:

These results should be considered as exploratory and interpreted with caution. This is because the included studies were of short duration, small and at risk of bias (where there was a risk of arriving at the wrong conclusions because of favouritism by the participants or researchers).

Authors’ conclusions:

The limited evidence comes from small, short-term, low-quality studies. There is some evidence that yoga has favourable effects on diastolic blood pressure, HDL cholesterol and triglycerides, and uncertain effects on LDL cholesterol. These results should be considered as exploratory and interpreted with caution.

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Yoga and scoliosis:

Dr. Loren Fishman, who studied with B.K.S. Iyengar in Pune, India, applies his yogic experience to his specialty of Rehabilitation Medicine. In a recent study of scoliosis patients, he found that a daily practice of holding Vasisthasana (Side Plank Pose) led to marked improvement in spinal curvature. Dr. Fishman’s peer-reviewed research focused on 25 patients with idiopathic and degenerative types of scoliosis, with curvatures from 6 to 120 percent. All patients improved, with the greatest improvement (up to 49 percent) noted in those who adhered to the daily regimen.

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Yoga and inflammation:

A study from Ohio State University found that practicing yoga for as little as three months can reduce fatigue and lower inflammation in breast cancer survivors. The more the women in the study practiced yoga, the better their results.  The research team focused on breast cancer survivors because the rigors of treatment can be so taxing on patients. “Though many studies have suggested that yoga has numerous benefits, this is the largest known randomized controlled trial that includes biological measures,” said Janice Kiecolt-Glaser, professor of psychiatry and psychology at The Ohio State University and lead author of the study. The participants of the Ohio study had completed all breast cancer treatments before the start of the study. Only yoga novices were recruited for the randomized, controlled clinical trial. At the six-month point of the study—three months after the formal yoga practice had ended—results showed that on average, fatigue was 57 percent lower in women who had practiced yoga compared to the non-yoga group, and their inflammation was reduced by up to 20 percent. Chronic inflammation is linked to numerous health problems, including coronary heart disease, Type 2 diabetes, arthritis and Alzheimer’s disease, as well as the frailty and functional decline that can accompany aging. To gauge the participants’ inflammation levels, the scientists measured the activation of three proteins in the blood that are markers of inflammation—called pro-inflammatory cytokines.

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Yoga practitioners at less risk of inflammatory diseases: a 2015 study:

Yoga practitioners are at lesser risk of developing inflammation that could lead to cardiovascular diseases, cancer and Alzheimer, a study by Indian Institute of Science (IIS) has revealed. The study found that regular exercise in the form of yoga can help optimise the levels of pro-inflammatory cytokines– Tumour Necrosis Factor (TNF) alpha and Interleukin-6 (IL-6). The results of the research indicate that yoga, which enhances mind-body relaxation achieved through a combination of proper breathing, meditation and physical exercises, can help keep TNF-alpha and IL-6 at optimal levels. The results showed that yoga practitioners fared better than non-yoga practitioners when it came to pro-inflammatory cytokine levels after a moderate-to-strenuous exercise trial.

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Yoga for rheumatic diseases: a systematic review 2013:

Yoga is widely used by patients with a variety of rheumatic diseases. According to the 2002 National Health Interview Survey, patients with rheumatic diseases were 1.56 times more likely to have practiced yoga within the last 12 months compared with the general population. The aim of this systematic review was to evaluate the quality of available evidence and the strength of the recommendation for yoga as a therapeutic means in the management of rheumatic diseases. Eight RCTs with a total of 559 subjects were included; two RCTs had a low risk of bias. In two RCTs on FM (fibromyalgia) syndrome, there was very low evidence for effects on pain and low evidence for effects on disability. In three RCTs on OA (osteoarthritis), there was very low evidence for effects on pain and disability. Based on two RCTs, very low evidence was found for effects on pain in RA (rheumatoid arthritis). No evidence for effects on pain was found in one RCT on CTS. No RCT explicitly reported safety data.  Based on the results of this review, only weak recommendations can be made for the ancillary use of yoga in the management of FM syndrome, OA and RA at this point.

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Effects of yoga interventions on pain and pain-associated disability: a meta-analysis 2011:

Authors searched databases for controlled clinical studies, and performed a meta-analysis on the effectiveness of yoga interventions on pain and associated disability. Five randomized studies reported single-blinding and had a higher methodological quality; 7 studies were randomized but not blinded and had moderate quality; and 4 nonrandomized studies had low quality. In 6 studies, yoga was used to treat patients with back pain; in 2 studies to treat rheumatoid arthritis; in 2 studies to treat patients with headache/migraine; and 6 studies enrolled individuals for other indications. All studies reported positive effects in favor of the yoga interventions. With respect to pain, a random effect meta-analysis estimated the overall treatment effect at SMD = -0.74 (CI: -0.97; -0.52, P < .0001), and an overall treatment effect at SMD = -0.79 (CI: -1.02; -0.56, P < .0001) for pain-related disability. Despite some limitations, there is evidence that yoga may be useful for several pain-associated disorders. Moreover, there are hints that even short-term interventions might be effective. Nevertheless, large-scale further studies have to identify which patients may benefit from the respective interventions. This meta-analysis suggests that yoga is a useful supplementary approach with moderate effect sizes on pain and associated disability.

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Yoga and cancer:

Earlier reviews have reported that yoga is beneficial for people with cancer in managing symptoms such as fatigue, insomnia, mood disturbances and stress, and improving quality of life. Many cancer patients experience cancer-related psychological symptoms, including mood disturbances, stress, and distress.  Ledesma and Kumano showed mindfulness-based stress reduction programs may indeed be helpful for the mental health of cancer patients. Thus, yoga may have long-term psychological effects for patients with cancer. According to the some review, no significant differences were observed on the measure of physical health. Because of the limited number of studies and different measurement tools, the effects of yoga on physical health in people with cancer remain unclear. Only one study examined the effects of yoga on physical fitness; therefore, future study could include outcome measures that not only include subjective feelings in questionnaires but also include physical performance, physical strength, endurance, and flexibility. All studies included in the meta-analysis investigated participants with a diagnosis of cancer; however, the types of cancer varied among studies. Of the 10 included studies, 7 investigated breast cancer, 2 recruited mixed cancer populations, and 1 included patients with lymphoma. The result of Cohen’s study on lymphoma showed no significant differences between groups in terms of anxiety, depression, distress, or fatigue; thus, it has little influence on our result. Therefore, since the majority of studies focused on breast cancer, future research needs to examine the use of yoga among male cancer patients and female non-breast cancer patients. In addition, various factors are associated with the execution of the intervention such as yoga styles and treatment doses that may influence effect size. Four different styles of yoga were used among the included studies: restorative, integrated, hatha, and Tibetan. Treatment dose, including duration and frequency, and the adherence to yoga intervention and home practice may also affect treatment outcome. According to the Carson’s study of yoga for women with metastatic breast cancer,  patients who practiced yoga longer on a given day were much more likely to experience less pain and fatigue and greater invigoration, acceptance, and relaxation on the next day. A 2009 review evaluated 10 studies which explored the impact of yoga on the psychological adjustment of cancer patients. Positive results were found in relation to improved sleep, quality of life and stress levels, improved mood, increased energy and acceptance of their condition. In summary, most of the studies show potential benefits of yoga for people with cancer in improvements in psychological health. But, more attention must be paid to the physical effects of yoga and the methodological quality of future research, as well as to improve these areas in the future.

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Yoga for breast cancer patients and survivors: a systematic review and meta-analysis of year 2012:

Twelve RCTs with a total of 742 participants were included. Seven RCTs compared yoga to no treatment; 3 RCTs compared yoga to supportive therapy; 1 RCT compared yoga to health education; and 1 RCT compared a combination of physiotherapy and yoga to physiotherapy alone. Evidence was found for short-term effects on global health-related quality of life (SMD = 0.62 [95% CI: 0.04 to 1.21]; P = 0.04), functional (SMD = 0.30 [95% CI: 0.03 to 0.57), social (SMD = 0.29 [95% CI: 0.08 to 0.50]; P < 0.01), and spiritual well-being (SMD = 0.41 [95% CI: 0.08; 0.74]; P = 0.01). These effects were, however, only present in studies with unclear or high risk of selection bias. Short-term effects on psychological health also were found: anxiety (SMD = −1.51 [95% CI: -2.47; -0.55]; P < 0.01), depression (SMD = −1.59 [95% CI: -2.68 to −0.51]; P < 0.01), perceived stress (SMD = −1.14 [95% CI:-2.16; -0.12]; P = 0.03), and psychological distress (SMD = −0.86 [95% CI:-1.50; -0.22]; P < 0.01). Subgroup analyses revealed evidence of efficacy only for yoga during active cancer treatment but not after completion of active treatment.

Conclusions: This systematic review found evidence for short-term effects of yoga in improving psychological health in breast cancer patients. The short-term effects on health-related quality of life could not be clearly distinguished from bias. Yoga can be recommended as an intervention to improve psychological health during breast cancer treatment.

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Yoga and epilepsy:

Epilepsy is a disorder where recurrent seizures are caused by abnormal electrical discharges in the brain. Most seizures can be controlled by antiepileptic drugs but sometimes seizures develop which are resistant to those drugs. People may also wish to try non-drug treatments such as yoga. It is widely accepted that stress can trigger seizures for many people with epilepsy. In one survey of 177 patients, 58 per cent identified that seizures occurred more frequently when they were stressed, with seizures occurring sometimes days or weeks later (Mattson, 1991). Similar studies also indicate that stress is the most frequent trigger of seizures, and is linked with sleep deprivation and fatigue (Frucht, Quigg, Schwaner & Fountain, 2000). In a more recent survey of 89 patients, 64 per cent of people with epilepsy reported that they believed stress increased the frequency of their seizures (Haut, Vouyiouklis & Shinnar, 2003); 32 per cent had tried stress reduction techniques, and of those who hadn’t, 53 per cent were willing to try. A variety of relaxation techniques exist which aim to relieve stress and tension, reduce blood pressure, and improve feelings of control over our lives. Workshops and classes in progressive muscular relaxation, meditation, yoga, tai chi, massage, and acupuncture can be found in increasing numbers. Many of these techniques have reported improved sleep, decreased aggravation and tension during the day, increased overall health, and reduced fear of seizures, indicating a greater sense of well-being (Rosseau, Hermann & Whitmann, 1985). In addition, the general observation that techniques like meditation are side effect-free (in contrast to drugs) is of great appeal. It is important to note that relaxation techniques are recommended as a complementary approach, and not a replacement to medication.  A Cochrane Review on relaxation therapy and seizure control indicates only possible beneficial effects on seizure frequency (Ramaratnam, Baker & Goldstein, 2005). An updated version of the original Cochrane review is published in 2012. No reliable evidence to support the use of yoga as a treatment for control of epilepsy. One single small trial showed modest benefits of Sahaja yoga over sham yoga and no intervention. Sample size is important because single small trials are unlikely to overcome the effects of chance; their results are likely to be misleading. Larger studies would be more informative.

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Yoga for sinusitis:

One of the most important Yoga practices for the prevention and management of sinusitis is the Neti Kriya that is one of the Shat Karmas of Hatha Yoga. Neti is the practice of cleaning the nasopharyngeal tract with liquids or thread. Types of Neti include Jala Neti (nasal irrigation with lukewarm saline water) and Sutra Neti (nasal cleaning with a thread or catheter. Others are Dugdha Neti (with milk), Ghrta Neti (with ghee) and Jala Kapalabhati that includes Vyutkrama and Seetkrama Kapalabhati. Hypertonic nasal irrigation is a therapy that flushes the nasal cavity with saline solution, facilitating a wash of the structures within. Originally part of the Yogic tradition as Neti, this technique is anecdotally regarded as safe and effective. It has been suggested as adjunctive therapy for sinusitis and sinus symptoms. Potential efficacy is supported by the observation that hypertonic saline improves mucociliary clearance, thins mucus, and may decrease inflammation. According to Dr. Marple, professor of otolaryngology at the University of Texas saline nasal irrigation is a highly effective, minimally invasive intervention for people suffering from nasal issues. David Shoseyov and colleagues have shown that hypertonic saline improves both clinical scores and plain Waters’ projection radiology scores in children with chronic sinusitis. They have also commented that the treatment is tolerable, inexpensive, and effective. A study by DG Heatley and colleagues in the University of Wisconsin has shown that daily nasal irrigation using a bulb syringe, nasal irrigation pot, and daily reflexology massage were equally efficacious and resulted in improvement in the symptoms of chronic sinusitis in over 70% of subjects. Medication usage was decreased in approximately one third of participants regardless of intervention. LT Tamooka and colleagues at the University of California have shown that patients who used nasal irrigation for the treatment of sinonasal disease experienced statistically significant improvements in 23 of the 30 nasal symptoms queried. Improvement was also seen in the global assessment of health status using the Quality of Well-Being scale. David Rabago and colleagues at the University of Wisconsin have shown that daily hypertonic saline nasal irrigation improves sinus-related quality of life, decreases symptoms, and decreases medication use in patients with frequent sinusitis.

Nada pranayama in sinusitis:

Chanting has always been an important aspect of the spiritual life in India. Chanting Mantras, performing Japa, singing Bhajans and the use of Nada Pranayamas such as the Bhramari and the Pranava are important parts of the Yogic life. Recent studies have shown that chanting creates sound vibrations that encourage air to move back and forth between the sinus membranes and nasal passages. This air movement helps open the tiny ducts, or ostia, that connect the nose to the sinuses, allowing the sinuses to drain properly. This can help prevent infections from settling down in the sinuses and create a healthy environment therein. All the sinuses are effectively ventilated by humming and this is an important benefit as previous research has shown that poor sinus ventilation increases the risk for sinusitis. When the sinuses are well ventilated infections have no chance of settling down at all. A study done by Jon Lundberg and Eddie Weitzberg of the Karolinska Institute in Sweden has shown that the daily humming or “Om” chanting may actually prevent infections from taking hold. They found that humming increased nitric oxide levels fifteenfold, compared to quiet exhalations without sound. The exhalations of people with healthy sinuses tend to have high nitric oxide levels, indicating that more air is able to flow between the sinuses and the nose. The Nada Pranayamas such as the Bhramari and the Pranava are similar to the humming used in the study. In the Bhramari Pranayama the nasal sound like a bee is used while in the Pranava Pranayama, the humming sounds of the Pranava A-U-M are used. This new light on humming and nasal ventilation can explain the scientific basis by which these Pranayamas can prevent as well as help in the management of sinusitis. This is another reason why practices like the Surya Namaskar should always be done with the chanting of the Surya Mantras and another reason why the chanting of the Mantras and scriptures should be encouraged in Yoga therapy and training.

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Clinical Applications of Yoga for the Paediatric Population: A Systematic Review of 2010:

Epidemiological research among adults suggests that many individuals use yoga for health maintenance and perceive benefit for overall health, musculoskeletal and mental health conditions.  Clinical trials with adults suggest potential benefit for various conditions including back pain, osteoarthritis, cardiovascular disease, and depression. In contrast, very little is known about the safety and efficacy of yoga among the paediatric population. A systematic review performed by Galantino and colleagues in 2008 identified 24 studies of yoga for children including case-control studies, pilot studies, cohort studies and randomized controlled trials (RCTs) that focused on studies of relevance to physical therapy. The review concluded that there was evidence for the benefit of yoga in the paediatric population in rehabilitation, but more research is necessary. This review differs from the recent systematic review of yoga for children published by Galantino et al. These authors used search terms related to yoga, paediatrics (children, developmental disabilities), exercise, and publication types that were of interest. Studies were included with primary outcomes of quality of life, cardio-respiratory fitness, and physical functioning or with secondary outcomes of attention and cognition. The review categorized studies based on relevance to physical therapy into three domains: neuromuscular, cardiopulmonary, and musculoskeletal headings. Preliminary evidence presented in this review suggests that yoga may be beneficial for physical fitness and cardio-respiratory health among children. As a physical form of exercise, studies suggest that yoga provides low aerobic intensity.  According to the 2002 NHIS, a large majority of adults who use yoga in the U.S. reported that yoga was important for their health maintenance. Based on this review, yoga may be an option for children to increase physical activity and fitness. In particular, yoga may be a gateway for adopting a healthy active lifestyle for sedentary children who are intimidated by more vigorous forms of exercise. However, studies have been predominately conducted in India, where yoga is culturally more acceptable and adaptable. Studies in different cultural settings are necessary to better evaluate the feasibility of yoga as a form of exercise for children.

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Yoga in school:

Yoga and meditation has been evaluated to be useful for children’s development. Some of the school related benefits include anti-bullying, emotional balance, decreasing school behaviour referrals, increasing ‘’time on task” and improvement in academic performance by reducing stress. Yoga has also been found to be differentiated from exercise in improving health related outcome measures. A 2005 review summarized the existing research indicating the benefits of programs including yoga to result in: increased self-esteem, better work habits, higher grade point average, decreased psychological stress, less aggressive behaviour, better attendance and decreased absences from school (Schoeberlein & Koffler, 2005).

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Yoga and weight loss:

In general, physical activity is better for preventing weight gain than it is for promoting weight loss, and it appears this also applies to yoga. Most types of yoga don’t have the same level of calorie-burning power as aerobic exercise does. Consider that a person who weighs 150 pounds (68 kilograms) will burn 240 calories in an hour of doing regular yoga, compared with 360 calories for an hour of aerobics. But any physical activity is good activity. Yoga will get you moving, after all, and it can provide health benefits such as improved blood lipid levels and enhanced mood. Regular physical activity should be part of any weight-loss plan. To lose weight, you want to reduce the calories you take in and increase the calories you burn. If you want to do yoga, the smart play is to include it in an exercise plan that includes aerobic activities, such as biking, jogging or swimming.

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Calorie Burn of Popular Exercises:

As you know, the number of calories that you burn is a major determinant of weight loss, and calorie burn is highly variable. For example, heavy people burn more calories because they have to carry more body weight. People with a genetically high metabolism also burn more calories, as do people with a higher percentage of lean muscle fibers. But to put yoga in a proper weight loss context, let’s examine the average calorie burn of basic familiar activity modes.

•Resting: At rest, you’ll burn 1 to 1.5 calories per minute (depending on your body weight) or 45 to 68 calories in 45 minutes.

•Walking slowly: Walking at a leisurely 2 miles per hour pace, you’ll burn 2 to 5 calories per minute, or 90 to 225 calories in 45 minutes.

•Walk briskly: Walking at a more brisk 4 miles per hour pace, you’ll burn 4.6 to 10 calories per minute, or 207 to 450 calories in 45 minutes.

•Running: Running at 6.7 miles per hour, you’ll burn 9 to 19 calories per minute, or 405 to 855 calories per hour.

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In 2005 and 2007, two separate studies measured the metabolic rate of people taking a beginner yoga class and found a calorie burn of 2.3-3.2 calories per minute, about the same calorie burn as strolling through the mall–or about 104-144 calories in a 45 minute workout. At this rate, to burn one pound (or 3500 calories) of fat, you’d have to perform over 28 hours of yoga!

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Could it be that yoga may actually slow your metabolism?

In fact, a 2006 study measured the metabolic rate of yoga people vs. non-yoga people, corrected for body weight, and found a 15% lower metabolism in the yoga group. To put this in context, that means that if you normally burn 2000 calories at rest, you might lower that calorie burn to 1700 calories at rest if you take up yoga. That is because yoga is a relaxing activity, and actually slows down your body’s “fight-and-flight” reactions, also known as your sympathetic nervous system. Although this is highly beneficial for extending your life span, controlling stress, and making you feel good, it’s certainly not going to shed any pounds.

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In hot yoga, or Bikram Yoga, the temperature in the yoga room is turned up higher than 105 degrees, with a recommendation of at least 40 percent humidity. As a result, people taking a hot yoga class experience more fatigue, a higher heart rate, and a significantly greater amount of exhaustion (not to mention body odour). But this relatively higher amount of perceived exertion is not really due to the fact that people are burning more calories. As a matter of fact, by simply walking into a hot room and standing for 45 minutes, your heart rate will significantly increase. That is because your body’s primary mode of cooling is to sweat and to shunt blood to your extremities. As you sweat, you lose blood volume, and as you shunt blood, your heart has to work harder to deliver that blood. And as a result your heart rate increases. But the increased heart rate is not due to you moving more muscles or burning more calories. It’s simply your body’s environmental, temperature-regulating response to hot conditions, and the only significant weight you’re going to lose in a hot yoga class is water weight. The calories you burn during yoga depend on your weight, the type of yoga you practice and the amount of time you spend practicing it. Although the American Council on Exercise reports that Hatha yoga — the most gentle — only burns 144 calories per hour for a 150-pound person, Bikram yoga burns about 477 calories. Experts theorize that the hot temperature and high humidity of the Bikram yoga studio force the heart rate up, increasing calorie burn.

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Most people wouldn’t think of yoga as the best form of exercise for losing weight but scientific research is increasingly showing links between yoga and weight loss. The American Journal of Lifestyle Medicine, which recently reviewed several studies of yoga and weight loss, also concluded that yoga is a successful slimming tool, not only burning calories and enabling people to improve their performance in other sports, but making them more mindful of their bodies, which in turn may lead them to eat better.

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If calorie expenditure didn’t account for weight maintenance or loss, what did?

1. It reduces stress:

Yoga has proven to be an effective method of treating anxiety and lowering stress, which has a huge impact on your ability to shed pounds.  If your cortisol levels are through the roof because you’re stressed, it doesn’t matter how much you deprive yourself of food, you’re still not going to lose weight. And for those of us who turn to food in times of stress — whether consciously or not — frequent practise will help reduce the consumption of those extra calories. As you race through the day in high gear, your body can often secrete fight-or-flight hormones that can stress your organ systems, encourage overeating and fat storage, and wreak havoc on your bodily functions. In yoga, you activate the parasympathetic nervous system, which slows things down, permitting your body’s systems to take a rest.

2. It builds muscle:

Many people instinctively turn to cardio-based exercise when they are trying to lose weight because it burns more calories in a shorter period of time than resistance training. However, building muscle mass through strength-based activities like yoga is just as beneficial because, in the end, muscle burns more calories than fat. Through continual practise, your muscles will also begin to lengthen and get toned, leaving you looking slim and trim. The physical strength and fitness you acquire through practising yoga might also encourage you to pursue other forms of exercise.

3. It teaches discipline:

A few months into practising yoga you may notice that the mental aspects of yoga — focus, restraint, clarity and calm — come to define your day-to-day mental state, and not just when you’re in the yoga studio. That same sense of discipline and mindfulness is essential to successful weight loss, especially when it comes to your eating habits.  As your mind and body become more in tune with one another, you might even notice a lack of interest in unhealthy foods. The researchers found a strong association between a regular yoga practice and mindful eating, which they did not find in other activities such as walking or running.

4. It encourages sound sleep:

Studies have shown that sleep deprivation affects your production of leptin, a hormone that tells your brain when you do or do not need food and slows your metabolism accordingly, putting you on the fast track to obesity. The meditative qualities of yoga help create a quieter mind, which lays the foundation for a good night’s rest. Try a few restorative poses before climbing into bed to achieve an extra-restful slumber.

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Yoga and weight loss studies:

1. Interestingly, research published in 2012 discovered that yoga has a beneficial impact on leptin, a hormone that plays a key role in regulating energy intake and energy expenditure. According to the authors, expert yoga practitioners had 36 percent higher leptin levels compared to novices, leading them to theorize that regular yoga practice may benefit your health by altering leptin and adiponectin production.

2. Study shows Yoga stimulates Weight Loss: a 2012 study:

A large public health study that included 15,550 adults aged 53 to 57 measured physical activity, including yoga and weight change over several years. Practicing yoga for four or more years was associated with a 3-lb lower weight gain among normal-weight participants (BMI of less than 25) and an 18.5-lb lower weight gain among overweight subjects. Regular yoga practice was associated with less weight gain with aging, especially in those who were overweight.

3. Restorative Yoga burns fat:

A 2013 study presented at the 73rd Scientific Sessions of the American Diabetes Association found restorative yoga burns subcutaneous fat and promotes weight loss in overweight women. Researchers at the University of California, San Diego, assigned 171 clinically obese women either to a restorative yoga program or stretching sessions for 48 weeks. The yoga and stretching groups practiced twice weekly for the first 12 weeks, twice monthly for the next six months, and then on their own for three months. Subcutaneous (fat directly under skin) and visceral (belly) fat measurements were obtained from the participants. Restorative yoga uses props, blankets, and bolsters to support the body, maximize stretch, and promote relaxation. The modified poses are less physically demanding for people with physical challenges. The researchers found the yoga group lost 34 square centimeters of subcutaneous fat, compared with 6 square centimeters for the stretch group. Furthermore, the yoga group lost more weight, an average of 1.7 kg, while the stretch group lost 0.7 kg. According to the American Journal of Managed Care, “One explanation for the difference may be that restorative yoga reduces levels of cortisol, which rises during times of stress and is known to increase abdominal fat.”

4. Yoga in the Management of Overweight and Obesity: 2014:

Although yoga may help manage conditions comorbid with overweight and obesity, such as low back pain, whether yoga helps with weight loss or maintenance beyond that which can be achieved with diet and exercise remains unclear. A search of multiple databases through September 2012 was undertaken identifying peer-reviewed studies on yoga, meditation, mindfulness, obesity, and overweight. Studies on yoga and weight loss are challenged by small sample sizes, short durations, and lack of control groups. In addition, there is little consistency in terms of duration of formal group yoga practice sessions, duration of informal practices at home, and frequency of both. Studies do however suggest that yoga may be associated with weight loss or maintenance. Mechanisms by which yoga may assist with weight loss or maintenance include the following: (a) energy expenditure during yoga sessions; (b) allowing for additional exercise outside yoga sessions by reducing back and joint pain; (c) heightening mindfulness, improving mood, and reducing stress, which may help reduce food intake; and (d) allowing individuals to feel more connected to their bodies, leading to enhanced awareness of satiety and the discomfort of overeating. Thus, yoga appears promising as a way to assist with behavioral change, weight loss, and maintenance.

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Yoga in gynaecology and obstetrics:

Yoga and menses:

Yoga practice during menstruation is a controversial issue. There are those who say that no woman should practice yoga during her menstruation, others say practice everything. In a yoga practice there are certain asanas that should be avoided during menstruation. The main type of asanas is inversions. These should be avoided throughout the menstruation. Secondly, any very strong asanas particularly strong backbends, twists, arm balances and standing positions that put a lot of stress on the abdominal and pelvic region should be avoided, especially if the woman is going through a lot of pain at the time.

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Is it safe to do yoga during pregnancy?

Yes. Yoga can be very beneficial during pregnancy, as long as you take certain precautions. Yoga helps you breathe and relax, which in turn can help you adjust to the physical demands of pregnancy, labor, birth, and motherhood. It calms both mind and body, providing the physical and emotional stress relief your body needs throughout pregnancy.

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Prenatal yoga:

Prenatal yoga can be a great way to prepare for childbirth. If you’re pregnant and looking for ways to relax or stay fit, you may be considering prenatal yoga. But did you know that prenatal yoga may also help you prepare for labor and promote your baby’s health? Before you start prenatal yoga, understand the range of possible benefits, as well as what a typical class entails and important safety tips.

What are the benefits of prenatal yoga?

Much like other types of childbirth-preparation classes, prenatal yoga is a multifaceted approach to exercise that encourages stretching, mental centering and focused breathing. Research suggests that prenatal yoga is safe and can have many benefits for pregnant women and their babies.

For example, studies have suggested that prenatal yoga can:

•Improve sleep

•Reduce stress and anxiety

•Increase the strength, flexibility and endurance of muscles needed for childbirth

•Decrease lower back pain, nausea, carpal tunnel syndrome, headaches and shortness of breath

•Decrease the risk of preterm labor, pregnancy-induced hypertension and intrauterine growth restriction — a condition that slows a baby’s growth

Prenatal yoga can also help you meet and bond with other pregnant women and prepare for the stress of being a new parent.

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In general, these poses are safe in pregnancy:

Butterfly stretch

Cat-Cow

Cobra (in the first trimester, if you feel comfortable doing this face-down pose)

Seated forward bend (with modifications as described above)

Side angle pose

Standing forward bend (with chair for modification)

Triangle pose (with chair for modification)

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Are any yoga postures unsafe during pregnancy?

The following postures and positions are not recommended during pregnancy:

•Lying on your back after 16 weeks.

•Breathing exercises that involve holding your breath or taking short, forceful breaths.

•Strong stretches or difficult positions that put you under strain.

•Lying on your tummy (prone).

•Upside-down postures (inversions).

•Back bends.

•Strong twists.

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Yoga and pregnancy studies:

1. Narendran et al. found that yoga practices including physical postures, breathing, and meditation practiced by pregnant women 1 h daily resulted in an increase in birth weight, decrease in preterm labor, and decrease in IUGR either in isolation or associated with PIH, with no increased complications.

2. Beddoe et al. found that women practicing yoga in their second trimester reported significant reductions in physical pain from baseline to post intervention. Women in their third trimester showed greater reductions in perceived stress and trait anxiety. From this, it is clear that yoga can be used to prevent or reduce obstetric complications.

3. Effect of integrated yoga on stress and heart rate variability in pregnant women: 2009:

The 122 healthy women recruited between the 18th and 20th week of pregnancy at prenatal clinics in Bangalore, India, were randomized to practicing yoga and deep relaxation or standard prenatal exercises 1-hour daily. The results for the 45 participants per group who completed the study were evaluated by repeated measures analysis of variance. Perceived stress decreased by 31.57% in the yoga group and increased by 6.60% in the control group (P = 0.001). During a guided relaxation period in the yoga group, compared with values obtained before a practice session, the high-frequency band of the heart rate variability spectrum (parasympathetic) increased by 64% in the 20th week and by 150% in the 36th week, and both the low-frequency band (sympathetic), and the low-frequency to high-frequency ratio were concomitantly reduced (P < 0.001 between the 2 groups). Moreover, the low-frequency band remained decreased after deep relaxation in the 36th week in the yoga group. Yoga reduces perceived stress and improves adaptive autonomic response to stress in healthy pregnant women.

4. Yoga for prenatal depression: a systematic review and meta-analysis: 2015:

Six RCTs were identified in the systematic search. The sample consisted of 375 pregnant women, most of whom were between 20 and 40 years of age. The diagnoses of depression were determined by their scores on Structured Clinical Interview for DSM-IV and the Center for Epidemiological Studies Depression Scale. When compared with comparison groups (e.g., standard prenatal care, standard antenatal exercises, social support, etc.), the level of depression statistically significantly reduced in yoga groups. Prenatal yoga intervention in pregnant women may be effective in partly reducing depressive symptoms.

5. A 2012 systematic review of yoga for pregnant women showed that studies indicate that yoga may produce improvements in stress levels, quality of life, aspects of interpersonal relating, autonomic nervous system functioning, and labor parameters such as comfort, pain, and duration. The findings suggest that yoga is well indicated for pregnant women and leads to improvements on a variety of pregnancy, labour, and birth outcomes. However, authors conclude that more randomized controlled trials are needed to provide more information regarding the utility of yoga interventions for pregnancy.

6. Relaxation techniques for pain management in labour: Cochrane Review 2011:

Relaxation and yoga may have a role with reducing pain, increasing satisfaction with pain relief and reducing the rate of assisted vaginal delivery. The pain of labour can be intense, with body tension, anxiety and fear making it worse. Many women would like to go through labour without using drugs, or invasive methods such as an epidural, and turn to complementary therapies to help to reduce their pain perception and improve management of the pain. Many complementary therapies are tried, including acupuncture, mind-body techniques, massage, reflexology, herbal medicines or homoeopathy, hypnosis, music and aromatherapy. Mind-body interventions such as relaxation, meditation, visualisation and breathing are commonly used for labour, and can be widely accessible to women through teaching of these techniques during antenatal classes. Yoga, meditation and hypnosis may not be so accessible to women, but together these techniques may have a calming effect and help the women to manage by providing a distraction from pain and tension. The review of eleven randomised controlled trials, with data reported on 1374 women, found that relaxation techniques and yoga may help manage labour pain. However, in these trials there were variations in how these techniques were applied in the trials. Single or limited number of trials reported less intense pain, increased satisfaction with pain relief, increased satisfaction with childbirth and lower rates of assisted vaginal delivery. More research is needed.

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Yoga and polycystic ovary syndrome (PCOS):

PCOS is a common hormonal disorder characterized by an enlarged ovary filled with small cysts. A PCOS woman can suffer from psychological, reproductive and metabolic consequences due to hormonal disturbances.  Poor hormonal signalling can result in high level of male hormone and insulin resistance. This results in hirsutism, acne, irregular menstrual cycles, and propensity to weight gain and infertility. Stress is attributed as a major cause for hormonal imbalance. Stressed out working women of modern era are highly susceptible to PCOS. On the contrary, striking PCOS symptoms also lead to stress and depression. Yoga eases any stress through breathing techniques that bring complete relaxation within the body. Relaxation can work to offset the effects of hormonal imbalance and take care of any negative emotions, irritability and frequent mood swings. Yoga is recognized as a complementary treatment in combating PCOS and help to prevent symptoms from getting worse due to the following health benefits:

•Yoga modifies glandular function so that the endocrine system works at maximum efficacy and accords the hormonal secretions.

•Yoga brings harmony within the body, mind and emotions to control PCOS naturally.

•Yoga assists in optimization in lifestyle by enhancing body awareness and self-care.

•Yoga brings peace and comfort and hence a path to healing painful symptoms of PCOS.

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Recommended asanas for PCOS are:

•Badhakonasana (Butterfly pose)

•Suptabadhakonasana (Reclined bound angle)

•Bharadvajasana (Bharadvajasana twist’s)

•Chakki Chalanasana (Mill churning pose)

•Shavasana (Corpse pose)

•Padma Sadhana

Practicing these asanas will become a reason to boost the health of the pelvic organs such as uterus and ovaries and improve functioning of the endocrine glands. Coupled with relaxation techniques, yoga promotes good health and perks up energy levels.

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Menopause:

A preliminary study at the University of California, San Francisco, found that menopausal women who took two months of a weekly restorative yoga class, which uses props to support the postures, reported a 30 percent decrease in hot flashes. A four-month study at the University of Illinois found that many women who took a 90-minute Iyengar class twice a week boosted both their energy and mood; plus they reported less physical and sexual discomfort, and reduced stress and anxiety. A Cochrane review examined the effects of exercise on hot flashes and found 2 RCTs using yoga as a treatment modality. Neither one found statistically significant differences between the yoga groups and conventional exercise groups. The authors concluded there was insufficient evidence to show yoga was more effective than other forms of exercise on vasomotor symptoms of menopause. However, a large RCT included in the Cochrane review did show lower stress levels and decreased overall symptoms in the yoga arm. The yoga intervention in this study consisted of pranayama, sun salutation (a repetitive sequence of 12 yoga postures), and cyclic meditation. Lee et al reviewed the 2 studies used in the Cochrane paper as well as 5 other studies. Two were RCTs showing that yoga intervention was not superior to a no-treatment control. Four studies showed favorable results for yoga interventions; however, one was a nonrandomized controlled trial and 3 lacked control groups. Cramer et al attempted pooled analysis of 5 studies, including those in the Cochrane paper, with similar results: Yoga interventions were not efficacious for somatic, vasomotor, or urogenital symptoms of menopause. Yoga was somewhat efficacious for psychological symptoms associated with menopause. More recently, an RCT (N=249) found that yoga reduces vasomotor symptoms no more frequently than non-yoga exercise.

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Yoga and sex:

Sexual abstention:

Traditionally, yogic training involved deferring the tantric practices of sexual yoga/marriage until such time that sexual self-mastery had been established, whereupon sexual union is considered to be the ultimate yoga of Shiva and Shakti. Brahmacharya for yogis, as stated in the Agni-Purana, embodies self-imposed abstention from sexual activity: fantasizing, glorifying the sex act or someone’s sexual attraction, dalliance, sexual ogling, sexually flirtatious talk, the resolution to break one’s vow, and consummation of sexual intercourse itself, with any being. Married practitioners aspire likewise to abstain from unconscious/harmful sexual behavior, and to meditatively practice sexual yoga (as opposed to ego-centered sexual release) with their partner, but must practice aware chastity with regard to others.

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Yoga and sexual performance:

One way to improve your performance in the bedroom is to translate all those relaxation and breathing techniques from yoga class into better, longer sex. Yogi Cameron says these strengthened concentration skills will help you focus your mind and better channel your sexual energy, helping to prevent premature ejaculation. “This can lead to increased sexual endurance,” he says, “and will make you far more sensitive and responsive to your partner.”  Studies have found that 12 weeks of yoga can improve sexual desire, arousal, performance, confidence, orgasm and satisfaction for both men and women. How? Physically, yoga increases blood flow into the genital area, which is important for arousal and erections, and strengthens pelvic floor muscles. Mentally, the breathing and mind control involved with the practice can also improve performance.  New Delhi-based yoga expert Deepak Jha advised more yoga postures to enhance sexual pleasure. “Postures like Paschimottanasana (seated forward bending), Halasana (plow) and Bhujangasana (cobra) help release sex hormone testosterone faster in men and also strengthen the genitalia,” Jha says. In fact, according to an abstract published recently in the journal Wiley, yoga practices can be invaluable in prolonging sexual stamina and pleasure. The yoga postures reduce the stress hormone cortisol which means less stress and better sleep. These also help release the essential hormone Oxytocin (“love hormone”) that relieves anxiety, enhances desire for social interaction and increases sexual intimacy. Global research also supports the sex-enhancing benefits of yoga. In two studies published recently in the Journal of Sexual Medicine, more than 100 men and women aged 20 to 60 were enrolled in a 12-week yoga camp. They were asked to complete questionnaires about their sexual satisfaction before and after the camp. The scores in all areas of sexual function – arousal, satisfaction, performance, confidence, ejaculatory control and orgasm – were significantly improved after yoga practice, the authors found.

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Game-changing systemic reviews:

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Effects of Yoga on Mental and Physical Health: A Short Summary of Reviews: 2012:

Majority of the research on yoga as a therapeutic intervention was conducted in India and a significant fraction of these were published in Indian journals, some of which are difficult to acquire for Western clinicians and researchers. In their bibliometric analysis from 2004, authors found that 48% of the enrolled studies were uncontrolled, while 40% were randomized clinical trials (RCT), and 12% non-RCT (N-RCT). Despite a growing body of clinical research studies and some systematic reviews on the therapeutic effects of yoga, there is still a lack of solid evidence regarding its clinical relevance for many symptoms and medical conditions. For many specific indications and conditions, there is inconsistent evidence with several studies reporting positive effects of the yoga interventions, but other studies are less conclusive. In some instances, these discrepancies may result from differences between the study populations (e.g., age, gender, and health status), the details of the yoga interventions, and follow-up rates. In this review, authors summarize the current evidence on the clinical effects of yoga interventions on various components of mental and physical health. In general, the respective reviews and an Agency for Healthcare Research and Quality Report (AHRQ) evidence report on “Meditation Practices for Health,” which cites also studies on yoga, include a heterogeneous set of studies with varying effect sizes, heterogeneous diagnoses and outcome variables, often limited methodological quality, small sample sizes, varying control interventions, different yoga styles, and strongly divergent duration of interventions.

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Systematic reviews for the different domains:

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These reviews suggest a number of areas where yoga may be beneficial, but more research is required for virtually all of them to more definitively establish benefits. However, this is not surprising given that research studies on yoga as a therapeutic intervention have been conducted only over the past 4 decades and are relatively few in number. Typically, individual studies on yoga for various conditions are small, poor-quality trials with multiple instances for bias. In addition, there is substantial heterogeneity in the populations studied, yoga interventions, duration and frequency of yoga practice, comparison groups, and outcome measures for many conditions (e.g., depression and pain). Disentangling the effects of this heterogeneity to better understand the value of yoga interventions under various circumstances is challenging. For many conditions, heterogeneity and poor quality of the original trials indicated that meta-analyses could not be appropriately conducted. Nevertheless, some RCTs of better quality found beneficial effects of yoga on mental health. Further investigations in this area are recommended, particularly because of the plausibility of the underlying psychophysiological rationale (including the efficacy of frequent physical exercises, deep breathing practices, mental and physical relaxation, healthy diet, etc.). This report summarizes the current evidence on the effects of yoga interventions on various components of mental and physical health, by focussing on the evidence described in review articles. Collectively, these reviews suggest a number of areas where yoga may well be beneficial, but more research is required for virtually all of them to firmly establish such benefits. The heterogeneity among interventions and conditions studied has hampered the use of meta-analysis as an appropriate tool for summarizing the current literature. Nevertheless, there are some meta-analyses which indicate beneficial effects of yoga interventions, and there are several randomized clinical trials (RCT’s) of relatively high quality indicating beneficial effects of yoga for pain-associated disability and mental health. Yoga may well be effective as a supportive adjunct to mitigate some medical conditions, but not yet a proven stand-alone, curative treatment. Larger-scale and more rigorous research with higher methodological quality and adequate control interventions is highly encouraged because yoga may have potential to be implemented as a beneficial supportive/adjunct treatment that is relatively cost-effective, may be practiced at least in part as a self-care behavioral treatment, provides a life-long behavioural skill, enhances self-efficacy and self-confidence and is often associated with additional positive side effects.

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The effectiveness of yoga in modifying risk factors for cardiovascular disease and metabolic syndrome: A systematic review and meta-analysis of randomized controlled trials: year 2014:

Yoga, a popular mind-body practice, may produce changes in cardiovascular disease (CVD) and metabolic syndrome risk factors. This was a systematic review and random-effects meta-analysis of randomized controlled trials (RCTs).

Methods:

Electronic searches of MEDLINE, EMBASE, CINAHL, PsycINFO, and The Cochrane Central Register of Controlled Trials were performed for systematic reviews and RCTs through December 2013. Studies were included if they were English, peer-reviewed, focused on asana-based yoga in adults, and reported relevant outcomes. Two reviewers independently selected articles and assessed quality using Cochrane’s Risk of Bias tool.

Results:

Out of 1404 records, 37 RCTs were included in the systematic review and 32 in the meta-analysis. Compared to non-exercise controls, yoga showed significant improvement for body mass index (−0.77 kg/m2 (95% confidence interval −1.09 to −0.44)), systolic blood pressure (−5.21 mmHg (−8.01 to −2.42)), low-density lipoprotein cholesterol (−12.14 mg/dl (−21.80 to −2.48)), and high-density lipoprotein cholesterol (3.20 mg/dl (1.86 to 4.54)). Significant changes were seen in body weight (−2.32 kg (−4.33 to −0.37)), diastolic blood pressure (−4.98 mmHg (−7.17 to −2.80)), total cholesterol (−18.48 mg/dl (−29.16 to −7.80)), triglycerides (−25.89 mg/dl (−36.19 to −15.60), and heart rate (−5.27 beats/min (−9.55 to −1.00)), but not fasting blood glucose (−5.91 mg/dl (−16.32 to 4.50)) nor glycosylated hemoglobin (−0.06% Hb (−0.24 to 0.11)). No significant difference was found between yoga and exercise. One study found an impact on smoking abstinence.

Conclusions:

There is promising evidence of yoga on improving cardio-metabolic health. Findings are limited by small trial sample sizes, heterogeneity, and moderate quality of RCTs.

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Yoga could be as effective as cycling or brisk walks in reducing the risk of a heart attack or stroke, this new research suggests. This finding is significant as individuals who cannot or prefer not to perform traditional aerobic exercise might still achieve similar benefits in CVD risk reduction.  That could see it being used by groups such as the elderly or those with musculoskeletal or joint problems.  The ancient Indian practice is a potentially effective therapy for making it less likely that people will develop cardiovascular disease (CVD) and should be promoted for that purpose, experts say. The research, published in the European Journal of Preventive Cardiology, finds that the ease and low cost of doing yoga mean it could become a useful tool in reducing heart-related illness.  “This review helps strengthen the evidence base for yoga as a potentially effective therapy for cardiovascular and metabolic health,” say the authors, who are from the Netherlands and the US. “The British Heart Foundation said the findings showed yoga producing real benefits and that any form of physical activity that reduced the risk of cardiovascular disease should be encouraged.

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Overview of Systematic Reviews:

Yoga as a Therapeutic Intervention for Adults with Acute and Chronic Health Conditions: year 2013:

Authors searched for systematic reviews in 10 online databases, bibliographic references, and hand-searches in yoga-related journals. Included reviews satisfy Oxman criteria and specify yoga as a primary intervention in one or more randomized controlled trials for treatment in adults. The AMSTAR tool and GRADE approach evaluated the methodological quality of reviews and quality of evidence. Authors identified 2202 titles, of which 41 full-text articles were assessed for eligibility and 26 systematic reviews satisfied inclusion criteria. Thirteen systematic reviews include quantitative data and six papers include meta-analysis. The quality of evidence is generally low. Sixteen different types of health conditions are included. Eleven reviews show tendency towards positive effects of yoga intervention, 15 reviews report unclear results, and no, reviews report adverse effects of yoga. Yoga appears most effective for reducing symptoms in anxiety, depression, and pain.  Although the quality of systematic reviews is high, the quality of supporting evidence is low. Significant heterogeneity and variability in reporting interventions by type of yoga, settings, and population characteristics limit the generalizability of results.

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Yoga injury:

While yoga has often been regarded as beneficial and without harm, this view has been challenged in recent years. Mainly based on anecdotal evidence, the safety of yoga has been questioned in a number of lay-press articles. In particular, a recent New York Times article by William J. Broad has listed a number of alarming cases of yoga-associated injuries. As these publications seem to have led to a general uncertainty among yoga practitioners and those interested in starting practice, it is important to systematically assess the safety of yoga. As any other physical or mental practice, yoga is not without risk. However, given the large number of practitioners worldwide, only relatively few serious adverse events have been reported in healthy individuals. Therefore, there is no need to discourage yoga practice for healthy people. It has however been stressed that yoga should not be practiced as a competition and that yoga teachers and practitioners should never push themselves (or their students) to their limits. Beginners should avoid advanced postures such as headstand or lotus position and advanced breathing techniques such as Kapalabathi. Practices like voluntary vomiting should perhaps be avoided completely. Most yoga injuries develop gradually because of poor yoga forms or overdoing certain asanas. The safest approach to yoga is to learn how to practice poses correctly, stay in tune with your body and avoid overdoing it. It is the most common reason why one ends up with back injury during yoga. Also, if one is unable to perform an asana, one should avoid it. As yoga has been shown to be beneficial for a variety of conditions, it can also be recommended to patients with physical or mental ailments, as long as it is appropriately adapted to their needs and abilities and performed under the guidance of an experienced and medically trained yoga teacher. Especially, patients with glaucoma should avoid inversions and patients with compromised bone and other musculoskeletal disorders should avoid forceful or competitive yoga forms. Yoga should not be practiced while under the influence of psychoactive drugs.

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Among the main reasons that experts cite for causing negative effects from yoga are beginners’ competitiveness and instructors’ lack of qualification. As the demand for yoga classes grows, many people get certified to become yoga instructors, often with relatively little training. Not every newly certified instructor can evaluate the condition of every new trainee in their class and recommend refraining from doing certain poses or using appropriate props to avoid injuries. In turn, a beginning yoga student can overestimate the abilities of their body and strive to do advanced poses before their body is flexible or strong enough to perform them. Vertebral artery dissection, a tear in the arteries in the neck which provide blood to the brain can result from rotation of the neck while the neck is extended. This can occur in a variety of contexts, but is an event which could occur in some yoga practices. This is a very serious condition which can result in a stroke. Acetabular labral tears, damage to the structure joining the femur and the hip, have been reported to have resulted from yoga practice.

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Hot yoga risk:

One of the primary risks associated with Bikram Yoga is that of dehydration and exhaustion from the heat. If you start a class without proper hydration or are a beginner, you do run this risk. But as a beginner, most classes will give you tips on how to handle the heat. If the asana is practiced in hot environment (temperatures about 105 degrees Fahrenheit) as it is done in some styles of Yoga, the heart rate, respiration rate and blood pressure increases, though muscles expand and one can stretch the body more, this may harm the muscles. Ideally the Yoga should be practiced in normal environmental conditions. This Hot Yoga, Bikram yoga or similar type is inappropriate and difficult to justify it as a version of ancient practice of Yoga.

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Adverse Events Associated with Yoga: A Systematic Review of Published Case Reports and Case Series: 2013:

While yoga is gaining increased popularity in North America and Europe, its safety has been questioned in the lay press. The aim of this systematic review was to assess published case reports and case series on adverse events associated with yoga. Medline/Pubmed, Scopus, CAMBase, IndMed and the Cases Database were screened through February 2013; and 35 case reports and 2 case series reporting a total of 76 cases were included. Ten cases had medical preconditions, mainly glaucoma and osteopenia. Pranayama, hatha yoga, and Bikram yoga were the most common yoga practices; headstand, shoulder stand, lotus position, and forceful breathing were the most common yoga postures and breathing techniques cited. Twenty-seven adverse events (35.5%) affected the musculoskeletal system; 14 (18.4%) the nervous system; and 9 (11.8%) the eyes. Fifteen cases (19.7%) reached full recovery; 9 cases (11.3%) partial recovery; 1 case (1.3%) no recovery; and 1 case (1.3%) died. As any other physical or mental practice, yoga should be practiced carefully under the guidance of a qualified instructor. Beginners should avoid extreme practices such as headstand, lotus position and forceful breathing. Individuals with medical preconditions should work with their physician and yoga teacher to appropriately adapt postures; patients with glaucoma should avoid inversions and patients with compromised bone should avoid forceful yoga practices.

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•Yoga is generally low-impact and safe for healthy people when practiced appropriately under the guidance of a well-trained instructor.

•Overall, those who practice yoga have a low rate of side effects, and the risk of serious injury from yoga is quite low. However, certain types of stroke as well as pain from nerve damage are among the rare possible side effects of practicing yoga.

•Women who are pregnant and people with certain medical conditions, such as high blood pressure, glaucoma (a condition in which fluid pressure within the eye slowly increases and may damage the eye’s optic nerve), and sciatica (pain, weakness, numbing, or tingling that may extend from the lower back to the calf, foot, or even the toes), should modify or avoid some yoga poses.

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Incidence of yoga injury:

Incidence rates of adverse events associated with yoga are best estimated from large prospective surveys of practitioners. However, these data are rare. In a small survey in 110 Finnish Ashtanga Vinyasa Yoga practitioners, 62% of respondents reported at least one yoga-related musculoskeletal injury, mainly sprains and strains. About half of those reported full recovery, the other half partial recovery. Ashtanga Vinyasa Yoga is a physically demanding yoga style that uses standardized sequences of physical yoga postures with synchronized breathing. More recently, in a large national survey, 78.7% of about 2500 Australian yoga practitioners indicated that they had never been injured during yoga. The remaining practitioners mainly reported minor injuries. 4.6% of respondents had been injured in the past 12 months; 3.4% reported injuries that occurred under supervision. In accordance with the present systematic review, the postures that were most commonly associated with injuries were headstand, shoulder stand and variations of the lotus pose. A survey in more than 1300 mainly North American yoga teachers and therapists found that respondents considered injuries of the spine, shoulders, or joints the most common; many respondents regarded yoga as generally safe and associated adverse events with excessive effort, inadequate teacher training, and unknown medical preconditions. An extensive survey of yoga practitioners in Australia showed that about 20% had suffered some physical injury while practicing yoga. In the previous 12 months 4.6% of the respondents had suffered an injury producing prolonged pain or requiring medical treatment. Headstands, shoulder stands, lotus and half lotus (seated cross-legged position), forward bends, backward bends, and handstands produced the greatest number of injuries. Systematic reviews on clinical trials on yoga interventions generally found insufficient reporting of safety data. However, if adverse events were reported, they could mostly be classified as non-serious.

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You can’t say that yoga puts people at great risk for injury without comparing it to the injury risk from other physical activities.  Indeed, when you look at the actual injury rates compared to other physical activities, yoga appears to be comparatively low risk. For example, in 2007 numbers, the injury rate for yoga was about 3.5 people out of every 10,000 practitioners. Compare that to the injury rate for weight-training and golf of around 15 and 39 respectively out of every 10,000 practitioners. So compared to other common physical activities, yoga appears to be much safer.

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Hot Yoga Risks:

Studios are often set to 105 degrees F and 40 percent humidity, which can be downright uncomfortable for some. With the high temperature also comes an increased risk of dehydration and heat stroke, making this style unsuitable for those with cardiovascular disease, hydration issues or a history of heat-related illness. If you opt for hot yoga, bring plenty of cold water, and head out the door for a break if you feel dizzy.

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Complications of yoga:

1. Subcutaneous emphysema:

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Radiograph showing air in the retropharyngeal space. A 40‐year‐old man developed swelling of the face and neck associated with respiratory distress of sudden onset. These symptoms followed a yoga exercise called “pranayam”, which had involved a vigorous Valsalva manoeuvre. Clinically, he had subcutaneous emphysema in the neck, more predominant on the right side, and tachypnoea. Cervical radiographs showed air in the retropharyngeal space, parapharyngeal spaces and subcutaneous emphysema. Chest radiograph showed pneumomediastinum.

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2. Isolated rupture of the lateral collateral ligament during yoga practice:

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Coronal T1-weighted magnetic resonance images of the knee showing avulsion of the lateral collateral ligament from its insertion on the fibular head (arrow).  A case is reported of isolated rupture of the lateral collateral ligament (LCL) of the knee while attempting to place the left foot behind the head during yoga practice. The 34-year-old man had discomfort of the lateral aspect of the knee particularly with varus strain. A magnetic resonance image revealed rupture of the LCL at the insertion onto the fibula.

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3. Yoga Foot Drop:

The common peroneal nerve is very vulnerable to injury, especially where it winds about the head of the fibula just below the knee. Pressure from sitting with the knees crossed, from kneeling, or from bizarre postures may readily affect this nerve. Susceptibility to damage from pressure is increased by weight loss, malnutrition, alcoholism, diabetes, and other causes of peripheral neuropathy. Recent experience indicates that common peroneal nerve injury may also result from a well-known Yoga practice (the kneeling pose), giving rise to what may be called “Yoga Foot Drop.” Yoga foot drop is a kind of drop foot, a gait abnormality. It is caused by a prolonged sitting on heels, a common yoga position of vajrasana. Yoga foot drop is one of a number of adverse effects of yoga, often unmentioned by yoga teachers and books.

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Here are some tips to avoid injury:

1. Move slowly and consciously. Rapid movements without attention lead to strains and sprains – and if you’re really unlucky, slipped disks in the back.

2. Ask teachers not to move your body for you, but rather to show by example and to instruct verbally. Forcing a body into a posture increases the likelihood of minor injuries like muscle pulls and torn ligaments. Teachers who insist on “hands on” work need to ask first before they touch (every time) and never move someone who has their eyes closed and their focus pointed inward.

3. Realize that Yoga is not a competition. It doesn’t matter what the person next to you is doing. And it doesn’t matter what you did three weeks ago before you went on vacation and haven’t practiced Yoga since. You’re not competing against your old record either. Let the gains be slow and gradual and real, not forced.

4. Don’t throw the head back too far into hyperextension. When the neck is extended (the face is pointed towards the ceiling), don’t roll or rotate the head. This is the one extremely long-shot way to cause a significant injury, specifically a tear of one of the arteries that feeds the brain leading to a stroke.

5. The neck needs to be protected in inverted postures, particularly sirsasana (headstand) and sarvangasana (shoulder stand). The body’s weight shouldn’t be on the neck. It can potentially lead to intervertebral disk damage and facet joint injury. Those bones aren’t designed to hold the full weight of the body. If they were, they would be big and thick like the lumbar vertebrae. Limit the time in these asanas or avoid them all together to avoid trauma. If practicing sarvagasana, use a folded blanket under the shoulders.

6. Avoid inversions during your period.

7. Try not to lock the knees. That can lead to cartilage damage and arthritis. While it may not be a problem for everyone, if you’re made with knees that straighten past the point of 180 degrees, then you may have trouble with the menisci over the long term. This is particularly true for more active forms of yoga and especially for any exercises that include jumps, pivots, or cutting out.

8. If you don’t feel good about a posture, don’t do it just to make your teacher happy or to avoid being the only one in class not doing it. Trust your instincts.  The extreme postures aren’t necessary.

9. If you have glaucoma, don’t do inverted postures. There is evidence that the increased pressure it causes in the eyes can worsen the disease and accelerate the onset of blindness. If you’re at risk of glaucoma, get your eyes checked before you turn upside down.

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Instructor fault versus inherently risky yoga poses:

“Anityasuciduhkhanatmasu nityasucisukhatmakhyatiravidya” (What at one time feels good or appears to be of help can turn out to be a problem; what we consider to be useful may in time prove to be harmful.) — From Patanjali’s Yoga Sutras, written in Sanskrit approximately 2000 years ago. Experts say under-qualified instructors are to blame as novices are encouraged to force their bodies into complicated positions they are not ready for. Doctors and physiotherapists have seen a rise in the number of patients injured in this way. Even popular positions such as the cobra and the plough, as well as headstands, can cause problems. There is a risk if an instructor is unqualified and doesn’t know the anatomy and physiology. You can’t possibly cover all that is required with just a short intensive course. Each person’s body is different in terms of suppleness and flexibility and they have to work within their limitations.  Anatomy experts also warn about the risks of inverted poses, which can strain cervical vertebrae or restrict blood flow into the head, either acutely or progressively. Investigations with yoga injuries have revealed certain yoga poses engage the body in positions that are unnatural for the design of the human body. A growing body of medical evidence supports the contention that, for many people, a number of commonly taught yoga poses are inherently risky. The first reports of yoga injuries appeared decades ago, published in some of the world’s most respected journals — among them, Neurology, The British Medical Journal and The Journal of the American Medical Association. The problems ranged from relatively mild injuries to permanent disabilities.

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Many people think yoga injuries are caused by people pushing too hard or from inexperienced teachers. These reasons are certainly true, but the biggest reason for yoga injuries is that the human body is not designed to be in the right angle poses that make up a huge percentage of modern yoga asana practice. Most yoga injuries are caused by putting the body in positions that are unnatural. According to exercise physiology, the most compressive position for the human spine is sitting down with the trunk at a right angle to straight legs. Forcing our curving bodies into square linear positions can cause an over-stretching of the ligaments of the spine, in particular ones that attach your sacrum to your hips. The lumbar spine and sacrum form an important shock-absorbing curve needed to keep your hip socket and knee joint from compressing. The oxymoron is that many yoga poses require you to place your body in this dangerous right angle position with the idea that your body will learn to “open”. This movement is not functional and has nothing to do with the way your body is designed to bend. We all need the lumbar curve and sacral platform to support our trunk and act as a shock absorber for the spine, hips, and knees. Poses like “Plow” are particularly dangerous because we create right angles between the neck and the trunk and the hips all at the same time. The weight of the lower body is dangerously positioned above a cervical spine that is not designed to hold more than about 15 pounds. People do use blankets and try not to compress the neck, but there are nerves getting tugged on passed the limit they can stretch, as well as cervical discs not designed to have that much pressure in extreme neck flexion for minutes at a time. Ligaments do not have a lot of sensory nerves, so we cannot feel when they are getting overstretched.

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Paschimottasana and Uttanasana are straight leg seated forward bending poses practiced from sitting or standing that go against how our body is “wired” to move. These poses and many variations are practiced with the compartmentalized idea that stretching the back while keeping the knees straight will lengthen the hamstrings and make the spinal column more flexible. When both knees are straightened and we stretch forward as in yoga forward bends, we are driving with our brakes on and stretching the ligament forces needed for natural anatomical function. Touching your toes is a waste of time and could prove to be harmful in the long run. All standing and seated forward bends with knees straight and ankles flexed in right angles undermine the spine’s integrity creating the C shape, or slouch, stressing the necessary ligament tension needed for natural joint functions of our spine, hips and knees.

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Inexperienced teachers and improper practice are the not only causes of yoga injuries.  Many yoga poses make no biomechanical sense and there is no way to do them ‘properly’. Taking the curve out of the sacral platform loosens the ligaments of the sacroiliac joint. Overtime, the loosed ligaments allow the sacral platform to fall and the natural 30-degree nutation angle needed for shock absorption disappears. After a period of years, many yoga practitioners began to feel SI joint and low back pain. In some it turns into hip compression, replacements and an undermining of the main support system in the body, the lumbar/sacral curve.

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Natural spine curves ought to be maintained to prevent injury:

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You ought to practice naturally aligned posture as the most important asana. If an asana does not support your spine in good posture, it is quite possibly working to pull your body out of alignment, and what is the benefit of doing it?

Three simple tests to determine whether a pose serves the human design:

1. It should allow the spine to maintain its natural curves.

2. It should not restrict the ability to do deep, rib-cage breathing.

3. It should have a real-life correlation to functional joint movement.

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Yoga sex abuse:

For many in the yoga community, yoga becomes an integral component of their ego/identity. If they acknowledge the systemic nature of sexual misconduct among many of modern yoga’s gurus, they may fear the consequences too great to bear. Key stakeholders in the yoga industry—instructors, trainers, and business owners—may fear the threat to their bottom line and personal livelihoods. Yoga practitioners and consumers may also fear the judgments others could develop about their beloved teachers, practices and identities. Yoga has a big following internationally and it’s truly tragic that yoga guru often abused his position and took advantage of young women. These young women are often vulnerable and looking for spiritual guidance. The worst thing about all these gurus and teachers is that they are not accountable to anyone. If they were a school teacher they would be promptly deregistered and never able to teach again. Be wary of who you trust.

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Sexual abuse in the yoga community has been a quiet but persistent issue since the practice came to the west in the 19th century. A yoga teacher has 30 ladies in a yoga class every day who all think he is evolved, spiritual, and special. Imagine the power he could have? There are no ethics committees or watchdog groups for yoga students, and yet teachers with huge power and influence are clearly taking advantage, and in some cases, even sexually assaulting their students who came to class to get fit or relieve stress.

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Turning a blind-eye on abuse may be far more complex than desensitization. For some, the silence could reflect the difficulty of balancing satya (i.e., “what is true?”) vs. ahimsa (“don’t be so judgmental”). The inability to reconcile these may be complicated by another factor: Some teachers and practitioners may be concerned that to keep the brand (and perhaps, individual) identity intact, they must protect the lineage holders and remain silent. Other potential reasons for blind eye syndrome abound. We may feel uncomfortable criticizing those in power or feel unworthy to do so, not trusting in our own wisdom. Or perhaps, when our eyes flicker over painful headlines, as good yogis we conveniently choose “forgiveness” (i.e. forgetfulness), rather than “dwelling on the negative.”  Yet make no mistake: Turning a blind eye to the suffering inflicted by yoga’s gurus is exactly the same behavior that enables these behaviors to persist. Our silence suppresses the truth in our heart-mind that connects with others’ suffering, longs for justice, and weeps for expression when we gag our instincts to speak out. Silence strengthens our own mental entrapment and dependency along with the structures that enable oppression and suffering. When we focus excessively on the positive, turning our eyes from the pain and unsavoriness in our own hearts and the yoga community, we become participants in the cycle of abuse. For every abuse scandal in modern yoga, blind eye syndrome played a likely role. Clear seeing and speaking may require momentary sacrifice and discomfort, but is a minimal price to pay for your own safety, peace and liberation, as well as those of your communities.

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The last few years have been awash with yoga scandals as well-known yoga teachers and gurus have fallen from grace.

1. Bikram Choudhury, founder of Bikram Yoga:

Five women filed civil suits against Bikram in 2013 alleging incidents ranging from sexual assault to rape. The cases have yet to be heard. Bikram is famous for making off-colour sexual remarks.

2. Dr. Kausthub Desikachar, grandson of the godfather of Western Yoga, Krishnamacharya:

The Krishnamacharya Healing and Yoga Foundation made a public statement on September 22, 2012 saying

…we’ve been made aware of the varying allegations of sexual, mental and emotional abuse against Dr. Kausthub Desikachar. [Editor’s note: the allegations were made by four teacher trainees.] Upholding this tradition and approach in the field of Yoga and Therapy, the Krishnamachraya Healing and Yoga Foundation are taking these allegations very seriously. Seven months later, Kausthub was back with a new website, and a letter explaining his new beginning: I realise that some of the decisions that I have made in the past have not been consistent with the high standards that I usually set for myself. I also fully understand and acknowledge that these have had far reaching effects, way beyond myself. There is no way of changing this past. I wholeheartedly repent for what has happened.

3. Rodney Yee:

In 2002, Rodney was accused of having affairs with some of his yoga students. He divorced his wife of 24 years, Donna Fone, and went on to marry his former yoga student, Colleen Saidman. “In the past, I think I was conveniently ignorant,” says Yee, who has apologized for previous infidelities. “I was pretending to myself that I wasn’t sexual in class.” Now he turns down yoga retreats where the students hang out with the instructors all day, the very setting that gave rise to his affair with Saidman.

4. Swami Muktananda:

Oh Guru, Guru, Guru began Lis Harris’ 1994 New Yorker article on the controversy surrounding Swami Muktananda, founder of the Siddha Yoga Path. Introduced to America in the 1970s by Baba Ram Dass, Muktananda was known as the ‘Guru’s guru’ and was a widely respected teacher of meditation and yoga. However, many of his followers have since come out and claimed that Muktananda allowed, even encouraged, guns and violence into his ashrams, and grew rich and corrupt from his devotees work efforts. He also claimed to be completely celibate but it’s alleged that he regularly had sex with female devotees. Michael Dinga, an Oakland contractor who was head of construction for the ashram and a trustee of the foundation, said the guru’s sexual exploits were common knowledge in the ashram. “It was supposed to be Muktananda’s big secret,” said Dinga, “but since many of the girls were in their early to middle teens, it was hard to keep it secret.”

5. Swami Satchidananda:

Swami Satchidananda made it big in the USA in the lates 1960s when he was flown in by helicopter to be the opening speaker at Woodstock Music Festival. He went on to found the Yogaville ashram in Virginia and Integral Yoga institutes across the country and, with thousands of devotees, including Lauren Hutton and Carol King, was somewhat of a ‘Yoga superstar’. But by 1991, the situation had changed: Protesters waving placards (“Stop the Abuse,” “End the Cover Up”) marched outside a Virginia hotel where he was addressing a symposium. “How can you call yourself a spiritual instructor,” a former devotee shouted from the audience, “when you have molested me and other women?” Satchinanda always denied the accusations against him of sexual misdemeanours, but many of his followers are reported to have left his ashrams and institutes after at least nine women claimed he had sexually abused them.

6. Swami Rama:

Described as “a tall man with a strikingly handsome face” Swami Rama founded the Himalayan Institute of Yoga Science and Philosophy, based in Pennsylvania with centers worldwide, as well as various service and teaching organizations. He was also one of the first Yogis to be studied by Western scientists. Journalist Katharine Websyter spent two years investigating the allegations of sexual abuse against Swami Rama, publishing an article in a 1990 edition of Yoga Journal that documented the experiences of women abused by Rama. A final blow to Rama’s reputation came just after his death in 1996, when a jury awarded nearly $1.9 million to a young woman who claimed she had been forced to have sex with him up to thirty times when living at the Himalayan Institute in 1993. He would fixate on a woman and make her a sort of valet, and then he would tell her it was necessary to perform these acts to further her spiritual development,” said Cliff Rieders of Williamsport, one of the woman’s lawyers.

7. Paramahansa Yogananda:

A yoga icon and founding father of yoga in the West, Yogananda introduced countless people to yoga with his renowned book ‘Autobiography of a Yogi’. He was also one of the first Indian yogis to make the move to the USA, spending much of the 1920s and 1930s lecturing and sharing his knowledge of Kriya yoga. There have been allegations that he fathered several ‘love children’ and that he ran a harem whilst on tour. The swami had young girls housed next to his room on the third floor of the former hotel, and how they went in and out of the swami’s room at all hours, while older women were housed on a separate floor.  However, DNA testing recently cleared Yogananda of fathering a child with a married disciple and evidence supporting the other claims against him is not well documented.

8. Swami Kriyananda:

Born James Donald Walters, Kriyananda was an American univeristy student who read ‘Autobiography of a Yogi’ and left everything to become a disciple of Yogananda. He later founded Ananda Sangha Worldwide. However, Kriyananda was reportedly ‘thrown out’ of Yogananda’s fellowship and was later sued for violating their copyrights by republishing the writings and recordings of Yogananda. He was also brought to court for the abuse of Anne-Marie Bertolucci, a former disciple, who claimed she was sexually abused by Kriyananda and another senior leader, and accused the fellowship of fraud. She won the case, and the Ananda Church was ordered to pay $1 million to Bertolucci as compensation.  The case was given added weight thanks to support from other ex-devotees. After Bertolucci filed suit, a dozen ex-Ananda members stepped up to support her case. Six women gave sworn testimony detailing various forms of what they considered sexual exploitation by the swami.

9. Swami Akhandananda Saraswati:

Swami Akhandananda was the spiritual leader of Mangrove Ashram, a Satyananda ashram in Australia, from 1974. In 1987 he was charged with 35 counts of sexual abuse against four girls, convicted and sent to prison. His conviction was later over turned by the Australian High Court on a technicality. The Swami died of alcoholism in the late 1990s. This particular case has recently been re-heard by the Royal Commission Inquiry in Australia. Disturbing details continue to emerge during a royal commission hearing about the sexual abuse of children in the 70s and 80s at a NSW yoga ashram. Nine abuse victims have told how former spiritual leader Swami Akhandananda used them for his sexual gratification.  At the inquiry, it was also alleged that many of the other adults at the ahsram, in particular the Swami’s partner Shishy, were aware of what was going on. Former child resident Alecia Buchanan testified that Shishy was often in the room while Akhandananda raped her. Plus, at the inquiry, fresh allegations have been made against Swami Satyananda himself of abuse, and allegations that his successor (Satyananda died in 2009) Swami Niranjananda entered into sexual relationships with at least one female disciple.

10. Swami Maheshwarananda:

Another ‘Yoga Rockstar’ Maheshwarananda is the founder of Yoga in Daily Life a humanitarian organisation with ashrams all over the world. A whistle blower set up a website on which several women posted shocking testimonies of alleged betrayal by Swamiji. It appeared the monk, whom ex-followers say claims to be celibate, had routinely abused his powerful status to exploit young female devotees for his own sexual pleasure. While none of these claims would amount to sexual assault, people began to leave. In Australia, a growing chorus of members demanded answers. About 18 senior figures who had been part of Yoga in Daily Life for up to 20 years resigned. This included the entire board. Some were forcibly expelled; other attendees simply stopped coming. Some centres closed down.

11. Swami Shankarananda:

The Guru and Director of the Mount Eliza ashram, Shankarananda has allegedly had sex with up to forty female followers. Although Shankarananda never claimed to be celibate, or demanded it from his students, the revelations have still deeply wounded his followers and community. The ashram is now being investigated over allegations of sexual abuse according to Australian newspaper The Age.

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My view:

Parents should be wary of yoga guru when they send their daughter for yoga classes. There is evidence to show that some modern yoga gurus are sexual predators and they coerce girls/women to have sex with them under disguise of promoting spiritual development.

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Discussion:

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The levels of scientific evidence:

There are four levels of evidence that can be offered for any scientific assertion or theory:

1. Testimony (anecdote)

2. Argument (hypothesis)

3. Correlation

4. Experimentation

These are listed in increasing levels of validity and acceptability. The anecdote is the weakest form of proof, while an experiment is the strongest. While weak, an anecdote is still evidence: and if your personal experience is that Yoga works for you, makes you healthier, cured your specific ailment, then you do yoga. In my article ‘complementary and alternative medicine’, I have stated that 30 % of illnesses are self-limiting and another 30 % are psychic in origin. Anecdotal experience works well in self-limiting illness and psychic illness, and when many people report anecdotal experiences, it appears as scientific fact. Many benefits of yoga belong to conglomeration of anecdotal reports.

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Factors that affect Scientific Research Studies:

Before examining any yoga research findings, you need to understand the essential components that constitute a scientifically valid study. This will enable you to critically evaluate the findings and determine whether a yoga research study is in keeping with the rigorous standards set by the scientific community. The gold standard of reliability in clinical research is what is known as the randomized controlled trial, or RCT. In an RCT, researchers randomly select subjects who are age and gender matched. Participants are then randomly assigned to receive one of several (two–three) treatment regimens or assigned to a control regimen. The control group is given a standard, established therapeutic modality; a placebo, or “sham” treatment; or no treatment at all. The most powerful RCTs are double-blind in nature, which means that neither the study subjects nor the researchers know who is getting what treatment.

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Levels of Evidence:

What do the levels of evidence describe? These are again standardized definitions that try to summarize the available published evidence in support of the given recommendations. They reflect the precision of the estimate of the treatment effect. The strongest weight of evidence (A) is assigned if there are multiple randomized trials with large numbers of patients. An intermediate weight (B) is assigned if there are a limited number of randomized trials with small numbers of patients, careful analyses of non-randomized studies, or observational registries. The lowest rank of evidence (C) is assigned when expert consensus is the primary basis for the recommendation.

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Classes of Recommendations:

What do the classes of recommendations I, II, and III mean? These are standardized classifications that were adopted by the ACC/AHA Task Force several years ago to ensure consistency across guidelines. Class I refers to conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective. In contrast, class III refers to conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/effective and in some cases may be harmful. Class II recommendations fall in between, and indicate conditions for which there is conflicting evidence or a divergence of opinion about the usefulness/efficacy of a procedure or treatment. Class IIa indicates that the weight of evidence/opinion is in favor of usefulness/efficacy. Class IIb indicates that the usefulness/efficacy is less well established by evidence/opinion. In simple terms, class I recommendations are the “dos,” class III recommendations are the “don’ts,” and class II recommendations are the “maybes.”

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The level of evidence is sometimes confused with the class of recommendation. The assignment of a C level of evidence to a class I recommendation should not be interpreted to mean that this is a “weak” recommendation. This may simply reflect the ethical or logistical difficulty of ever performing a randomized trial to test the treatment or procedure in question. For example, there is a class I recommendation in the Stable Angina Guideline for echocardiography in patients with a systolic murmur suggestive of aortic stenosis or hypertrophic cardiomyopathy, for which the level of evidence is a C. It is highly unlikely that any institutional review board would ever approve a randomized trial in which patients with suspected aortic stenosis were denied echocardiography.

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A variety of issues must be addressed when using science to study the effects of yoga practice.

Here are some of the most important of these issues:

Sample Size.

The results of studies that examine the effects of a treatment on a small group of people are not generally considered to be applicable to an entire population. Small sample sizes tend to be unable to detect subtle treatment effects. Systematic study of a large population of people is likely to give the most reliable results. Most of the studies published about yoga are significantly underpowered, with sample sizes comprising fewer than 100 participants.

Placebo Effect.

It is well established that a subject’s own belief that a treatment is going to work can have a powerful and measurable effect on the outcome of any study. It is impossible to “treat” a group of yoga subjects and avoid this placebo effect, since the practitioners are aware of the fact that they are doing yoga.

Sample Bias.

The RCT prefers to study a random population sample in order to minimize variables that might influence study outcomes. Many yoga studies recruit subjects from a yoga school or an ashram, which can lead to an inherent bias in the study group, as the subjects are not randomly selected.

Length of Treatment.

In many of the yoga studies conducted to date, conclusions about the effects or outcomes of a yoga practice have been drawn after an 8- to 12-week period of yoga “treatment.” Yoga practice may, in fact, take a significantly longer time period than this to make a difference.

Consistency of Treatment.

The “treatment” under study should be consistent and similar each time it is administered, in order to control variability, which could skew results. As many yoga participants and teachers know, several variables can affect a yoga practice. For instance, most studies involving yoga do not enumerate the poses that were utilized, how long they were held or which style of yoga was emphasized. This makes reproducing results impossible.

Holistic vs. Scientific.

Yoga is a multifaceted discipline, and the physical poses are just one aspect of a yoga practice. Many practitioners believe that scientifically quantifying the holistic changes that yoga practice may produce is impossible when you reduce the practice to a sequence of poses and study physical change.

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The bigger argument is that randomized, controlled trials — of any length — to study yoga don’t work, for various complex, holistic reasons that don’t sound very convincing to me. The alternative is observational studies. And as it happens, Moliver completed an award-winning PhD thesis at Northcentral University  that used an observational design — an online survey — to study yoga in 211 female yoga practitioners plus 182 controls. Observational studies have a lot of problems, in particular the inability to distinguish between cause and effect, as Moliver acknowledges. For example, if a researcher didn’t randomly assign the participants, it is not possible to know if Yoga practitioners are happier because they practiced Yoga, or if people who were happier were naturally attracted to starting a Yoga practice.

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Confounding variables:

Confounding variable or factor is interference by a third variable so as to distort the association being studied between two other variables, because of a strong relationship with both of the other variables. A confounding variable can adversely affect the relation between the independent variable (cause) and dependent variable (outcome/effect). This may cause the researcher to analyse the results incorrectly. The results may show a false correlation between the dependent and independent variables, leading to an incorrect rejection of the null hypothesis. Characteristics of yoga users, their diet, their disciplined life-style and absence of bad habits like smoking/alcoholism are confounding variables that affect yoga study results.

Characteristics of yoga users:

A result of a US national survey 2008 found that yoga users are more likely to be white, female, young and college educated. The Australian survey of 2012 asked respondents to describe their dietary and lifestyle choices and whether this choice had been influenced by their yoga practice. The proportion of respondents who were non-smoking, vegetarian or had a preference for organic foods was generally higher in those with more years of practice. A 2015 systematic review (55 studies) of demographic, health-related, and psychosocial factors associated with yoga practice found yoga use is greatest among women and those with higher socioeconomic status and appears favorably related to psychosocial factors such as coping and mindfulness. Yoga practice often relates to better subjective health and health behaviors but also with more distress and physical impairment.

In other words, people who practice yoga are generally young, healthy, educated, belonging to higher socio-economic strata of society, eating healthy diet, leading disciplined life and less likely to indulge in alcoholism/smoking. All these are confounding variables which directly affect results of yoga studies. For example, eating healthy food prevent weight gain. Your claim to maintain ideal weight due to yoga could be because of healthy food you eat rather than sham yoga you perform watching TV.

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The Myth of Sweating Toxins:

Does your yoga instructor tell you that the sweating is good for you because you are releasing toxins from the body? Well, this statement is not true. Most of what you are sweating is water, but there are other chemicals that make up sweat including salt, potassium, ammonia, and urea. True toxin elimination comes from the kidneys and liver, and some from the colon. Doing a ninety-minute hot yoga session and sweating to death is not releasing toxins. You really are just dehydrating yourself and losing only water weight.

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A Short Summary of Reviews in 2012 showed that a majority of the research on yoga as a therapeutic intervention was conducted in India and a significant fraction of these were published in Indian journals, some of which are difficult to acquire for Western clinicians and researchers. In their bibliometric analysis from 2004, they found that 48% of the enrolled studies were uncontrolled, while 40% were randomized clinical trials (RCT), and 12% non-RCT (N-RCT). Despite a growing body of clinical research studies and some systematic reviews on the therapeutic effects of yoga, there is still a lack of solid evidence regarding its clinical relevance for many symptoms and medical conditions. For many specific indications and conditions, there is inconsistent evidence with several studies reporting positive effects of the yoga interventions, but other studies are less conclusive. In some instances, these discrepancies may result from differences between the study populations (e.g., age, gender, and health status), the details of the yoga interventions, and follow-up rates. Take a look at systematic review articles and meta-analyses—studies that aggregate other studies—and you’ll see where the miraculous yoga cure really stands. The majority of such compilations both criticize the methodology of yoga research and find that yoga has little or no effect on serious illness.

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A 2014 systematic scoping review of yoga intervention components and study quality:

The scientific study of yoga requires rigorous methodology. This review aimed to systematically assess all studies of yoga interventions to (1) determine yoga intervention characteristics; (2) examine methodologic quality of the subset of RCTs; and (3) explore how well these interventions are reported. Searches were conducted through April 2012 in PubMed, PsycINFO, Ageline, and Ovid’s Alternative and Complementary Medicine database using the text term yoga, and through handsearching five journals. Original studies were included if the intervention (1) consisted of at least one yoga session with some type of health assessment; (2) targeted adults aged ≥18 years; (3) was published in an English-language peer-reviewed journal; and (4) was available for review. Of 3,062 studies identified, 465 studies in 30 countries were included. Analyses were conducted through 2013. Most interventions took place in India (n=228) or the U.S. (n=124), with intensity ranging from a single yoga session up to two sessions per day. Intervention lengths ranged from one session to 2 years. Asanas (poses) were mentioned as yoga components in 369 (79%) interventions, but were either minimally or not at all described in 200 (54%) of these. Most interventions (74%, n=336) did not include home practice. Of the included studies, 151 were RCTs. RCT quality was rated as poor. This review proved the inadequate reporting and methodologic limitations of current yoga intervention research, which limits study interpretation and comparability.

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The yoga studies contain myriad methodological problems, some of which are similar to those that plagued prayer research. First, what is yoga?  In a real practical sense, medical researchers have to agree on the elements essential to yoga practice before they can test it as a therapy. Is deep breathing or stretching the source of therapeutic benefit? Or maybe it’s simple exercise, which wouldn’t exactly be news. In addition yoga like prayer can’t be dosed in milligrams. How much yoga do you need to do, and for how long, to achieve a benefit? There’s also significant individual variation at play. Some people breathe more deeply, hold poses for longer, and meditate “better” than others. That’s going to muddy the statistics. Control and blinding are also problematic. When you test a pill for heart disease, you give some people the pill and others a placebo (or an existing medication). The patients can’t tell which group they’re in. When doing yoga study, those who do yoga know that they are doing yoga, and those not doing yoga know that they are not doing yoga, so the placebo effect of yoga cannot be eliminated.  And in a surprising number of yoga studies, the researchers aren’t blinded either, raising the risk of a second form of bias. Much of the research on yoga has taken the form of preliminary studies or clinical trials of low methodological quality, including small sample sizes, inadequate blinding, lack of randomization, and high risk of bias.

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A systematic review on the treatment of asthma with yoga was published in 2011. The author found that the methodology of the underlying studies was “mostly poor,” due to problems with blinding and randomization. High dropout rates also biased the results. In the only study included in the review that offered a credible placebo control—a nonyogic stretching regimen—yoga offered no benefit. The author of the review article concluded, “The belief that yoga alleviates asthma is not supported by sound evidence.” A review of yoga for the treatment of schizophrenia, published in 2013, noted that none of the underlying studies blinded participants, and only three of the five studies blinded the researchers. Dropout rates were either high or unreported. The authors concluded, “No recommendation can be made regarding yoga as a routine intervention for schizophrenia patients.” A 2013 review paper on yoga for hypertension complained that the “methodological quality of the included trials was evaluated as generally low,” and therefore “a definite conclusion about the efficacy and safety of yoga on hypertension cannot be drawn.” To be fair, the folks who review existing studies occasionally do conclude that yoga may have modest benefits for sufferers of some afflictions, but they almost always include a laundry list of gripes about methodology and offer the weakest possible recommendation.

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Why haven’t you already heard about all of these anti-yoga studies? They have no constituency, and therefore don’t interest the media much. When a journal article showing that yoga improves quality of life in breast cancer patients came out, hundreds of stories trumpeted the results in the mainstream media. Yet it’s difficult to find any mention of the review articles discussed above that question the efficacy of yogic practice as a health care tool. Few people wanted to read a sceptical take on therapeutic prayer in the 1990s, and there aren’t many people today who will click on stories about how yoga won’t solve their health problems. The negative studies never make it beyond medical journals. In other words, yoga hype is created by media and scientific evidence of yoga inefficacy is buried by media.  Doctors eventually realized—most of them, at least—that prayer didn’t fit well into a clinical trial. Yoga doesn’t, either. That doesn’t mean you shouldn’t do yoga. By all means, do yoga, if those things bring you contentment and stress reduction. Do yoga especially if it’s your preferred form of exercise—exercise is a health intervention supported by thousands of clinical trials.

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Yoga: from pseudoscientific physiology to real science:

‘Prana’ refers to the universal life force and ‘ayama’ means to regulate or lengthen. Prana is the vital energy needed by our physical and subtle layers, without which the body would perish. It is what keeps us alive. Pranayama is the control of prana through the breath. These techniques rely on breathing through the nostrils. Prana flows through thousands of subtle energy channels called ‘nadis’ and energy centers called ‘chakras’. The quantity and quality of prana and the way it flows through the nadis and chakras determines one’s state of mind. If the Prana level is high and its flow is continuous, smooth and steady, the mind remains calm, positive and enthusiastic. However, due to lack of knowledge and attention to one’s breath, the nadis and chakras in the average person may be partially or fully blocked leading to jerky and broken flow. As a result one experiences increased worries, fear, uncertainty, tensions, conflict and other negative qualities.  Regular pranayama practice increases and enhances the quantity and quality of prana, clears blocked nadis and chakras, and results in the practitioner feeling energetic, enthusiastic and positive. When energy becomes blocked in a chakra, it is said to trigger physical, mental, or emotional imbalances that manifest in symptoms such as anxiety, lethargy, or poor digestion. The theory is to use asanas to free energy and stimulate an imbalanced chakra. . More than just stretching and toning the physical body, the yoga poses open the nadis (energy channels) and chakras (energy centers) of the body. Yoga poses also purify and help heal the body, as well as control, calm and focus the mind. The different categories of postures produce different energetic, mental, emotional and physical effects.

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Well, well, well.

I am a student of science and medicine for decades. I have dissected dead bodies. I have examined and treated thousands of people. I have seen some of them dying before me. I want to assert that there is no prana, no nadi and no chakra. It is a pseudoscience. The only nadi I know is arterial pulse felt when heart pumps blood into large blood vessels. The sole purpose of heart is to pump blood and the sole purpose of lungs is to instil oxygen and remove carbon dioxide vis-à-vis blood. Heart (circulation) and lungs (respiration) have nothing to do with spirituality or consciousness. I have seen many patients brain dead (no spirituality/consciousness) yet heart beating. I have seen many patients with no breathing but kept alive on mechanical ventilator for weeks or months. Since time immortal, people used to die. When somebody dies thousands of years ago, the first symptom of death is absence of breathing. In other words, breath became associated with life. So manipulation of breath would result in manipulation of life. This is how pranayama came into existence by manipulating breath in different ways providing different benefits. To perform pranayama, our ancestors needed bodily postures, so asanas came into existence. So postures and breathing techniques were standardized and synchronized for optimal benefit. So far so good as far as pseudoscience is concerned. But inadvertently real science entered in yoga. The basic axiom of yoga is that breath gives us a tool with which we can explore the subtler structures of our mental and emotional worlds.  I challenge it. The job of lungs is to provide oxygen and remove carbon dioxide. Lungs have no relationship with mind functioning.  Rapid breathing is part of stress response to provide more oxygen and reverse is true for relaxation when breathing is normal. By voluntarily slowing respiratory rate to less than normal of 12 to 18 breaths per minute (in adults) with deep breathing does not provide any extra oxygen. Respiratory changes with stress and de-stress occurs due to neural connection between brain and lungs. Using same neural connection to reduce stress by deliberate slow deep breathing cannot de-stress. However concentrating on breathing activity by mind can fade out distractions in mind, some of which could be stressing distractions and therefore conscious breathing would shift focus from stressors and thereby reduce stress. I repeat conscious breathing and not deep slow breathing of yoga. Conscious breathing brings mind to breath control and remove distractions thereby reduce stress. Remember, our daily breathing is subconscious, that is we are unaware of it. What yoga does is to make you aware of breathing and bring your mind concentration on breath consequently disallowing distractions. So concentration on breath by mind results in removal of distracting thoughts and objects from mind leading to meditation and stress release. It is this de-stressing by yoga is real science and not asanas which are mere muscle stretching and isometric exercises. Ironically, majority of people practice yoga as exercise rather than meditation and therefore avail themselves of exercise benefit akin to walking rather than de-stressing benefit.  As discussed earlier, good qualified yoga teacher is a must to avoid injury and the same logic applies to prevent practice of sham yoga. Sham yoga would have no de-stress benefit but only exercise benefit akin to leisurely walking.

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Unwarranted credit:

Yoga is a classic example of unwarranted credit. 5000 years ago, nobody knew neurochemicals and neurotransmitters, sympathetic and parasympathetic nervous system etc. There was no science 5000 years ago. People were doing asanas, pranayama, meditation and benefits of yoga was attributed to pseudoscience of opening of nadiis and opening of blocked chakras to move prana freely. Today to say yoga was science since 5000 years is nothing but unwarranted credit given to ancestors. Yes, yoga is beneficial to us and we are grateful to ancestors for discovering it, but to say humans were so intelligent 5000 years ago that they discovered yoga scientifically is weird. 5000 years ago, humans even did not know that earth is spherical and revolves around sun. They used to believe that earth is flat and sun revolves around it.

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Meditation is a practice in which an individual trains the mind or induces a mode of consciousness, either to realize some benefit or for the mind to simply acknowledge its content without becoming identified with that content, or as an end in itself. The word meditation carries different meanings in different contexts. Meditation is a general term for a technique in which a person empties his mind of extraneous thought, with the intent of elevating the mind to a different level and transcends mundane concerns. Yoga is concentrative meditation, where the meditating person focuses attention on his or her breathing and in doing so, suppresses other thoughts. Yoga meditation is concentration on breathing resulting in removal of distracting thoughts. Mindfulness practice is another type of meditation where mind is allowed to wander, let thoughts come and go without reacting, judging or holding thoughts. Mindfulness meditation is practiced sitting with eyes closed, cross-legged on a cushion, or on a chair, with the back straight. Attention is put on the movement of the abdomen when breathing in and out, or on the awareness of the breath as it goes in and out the nostrils.  As thoughts come up, one returns to focusing on breathing. One passively notices one’s mind has wandered, but in an accepting, non-judgmental way. In mindfulness practice, you let your mind be aware of the sounds and activities around you without becoming too focused. The physician Jon Kabat-Zinn describes the difference between concentration and mindfulness (“floating concentration”) concisely:

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In relatively stable environments, concentration is the most important form of attention. If however there is persistent change in the environment, we need mindfulness to find those solutions, which are relevant to the modified environmental conditions. Concentration remains important in order to not float aimlessly in the maelstrom of change.

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Concentration and mindfulness meditations are distinctive and different from each other: 1999 study:

Electroencephalographic (EEG) recordings from 19 scalp recording sites were used to differentiate among two posited unique forms of mediation, concentration and mindfulness, and a normal relaxation control condition. Analyzes of all traditional frequency bandwidth data (i.e., delta 1-3 Hz; theta, 4-7 Hz; alpha, 8-12 Hz; beta 1, 13-25 Hz; beta 2, 26-32 Hz) showed strong mean amplitude frequency differences between the two meditation conditions and relaxation over numerous cortical sites. Furthermore, significant differences were obtained between concentration and mindfulness states at all bandwidths. Taken together, the results suggest that concentration and mindfulness “meditations” may be unique forms of consciousness and are not merely degrees of a state of relaxation.

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Many studies since the 1970′s have shown that a regular meditation or mindfulness practice reduces stress, stress-related illness, reduces blood pressure, heart disease, reduces depression, anxiety, the problems of diabetes, turns off the flight-or-fight response, improves wound healing, interpersonal relationships, coping skills, increases cognitive abilities, thickens the prefrontal cortex of the brain, … and on and on. While the studies documenting these benefits have been conducted on meditation, it is not a great leap to conclude that the time spent doing Yoga will tap into the same well of healing and wholeness that meditation provides.  An fMRI study found that Yogis had larger brain volume in the somatosensory cortex, which contains a mental map of our body, the superior parietal cortex, involved in directing attention, and the visual cortex, which might have been bolstered by visualization techniques. The hippocampus, a region critical to dampening stress, was also enlarged in practitioners, as were the precuneus and the posterior cingulate cortex, areas key to our concept of self. Another study on mindfulness practice (non-yoga) found that after spending an average of about 27 minutes per day practicing mindfulness exercise, the participants showed an increased amount of grey matter in the hippocampus in fMRI, which helps with self-awareness, compassion, and introspection. In addition, participants with lower stress levels showed decreased grey matter density in the amygdala, which helps manage anxiety and stress. This proves benefits of non-yoga meditation (i.e. without asanas and pranayama) in people to reduce stress & anxiety by changing brain plasticity. Another 2014 study found that fluid intelligence declined slower in yoga practitioners and meditators than in controls. The point I want to make is yoga or non-yoga meditation yield the same improvement in fluid intelligence. Relaxation induced by meditation is considered to be a powerful remedy in traditions such as Ayurveda/Yoga in India or Tibetan medicine by switching on disease-fighting genes but it is not yoga specific. Any genuine relaxation by any meditation would do the same.

To sum it up:

Both yoga (i.e. with asanas and pranayama) and non-yoga meditation (e.g. mindfulness practice) alter brain plasticity by increasing grey matter in hippocampus and reducing grey matter in amygdala to reduce stress and anxiety. Both yoga and non-yoga meditation  showed much less decline in fluid intelligence with age than did the controls resulting in improved mental health. Both yoga meditation and non-yoga meditation causes relaxation to switch on disease-fighting genes. So the issue is true meditation and true relaxation no matter whether you achieve it through yoga or other means.

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The research, led by Professor Myriam Hunink of Erasmus University Medical Center in Rotterdam and Harvard School of Public Health in Boston, was a review of 37 randomized studies involving 2,768 participants which found that yoga is linked to the reduction of key risk factors for heart disease, including lower body mass index (BMI), weight loss, improved cholesterol levels, lower blood pressure, and reduced heart rate. Researchers also found that when it came to these improved risk factors, there was not a significant difference between yoga and other forms of exercise. Though these new findings are encouraging (and for many teachers and practitioners, validating), they do raise certain questions as well. For instance, how does this work physiologically?  Why does yoga—which is not typically considered a cardiovascular exercise—reduce these risk factors?  I think stress reduction is a big piece of reducing cardiovascular disease risk. We think of aerobic exercise as being a way to make the heart stronger. And there’s truth to that. You increase your cardiovascular fitness by doing aerobic work—and we all need that. But the fact that people’s blood pressure and lipid profiles improved, and that they even lost weight by doing yoga (which probably wasn’t aerobic), says there’s something else happening. So it comes down to two things, that physical movement in general is positive, and that yoga practices reduce stress. We know that stress itself magnifies all the risk factors for heart disease. When you’re chronically stressed, your blood pressure goes up. Your cholesterol goes up because of the increase in cortisol. If we simply breathe, stretch, and relax—that is, do yoga—we decrease our risk for heart disease.

To sum it up:

Yoga has same benefits of aerobic exercise not only due to muscle stretching and isometric exercise but also due to stress reduction.

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Can aerobic exercise itself reduce stress?

Exercise is a form of physical stress by stimulating sympathetic nervous system.

Can physical stress relieve mental stress?

Regular aerobic exercise will bring remarkable changes to your body, your metabolism, your heart, and your spirits. It has a unique capacity to exhilarate and relax, to provide stimulation and calm, to counter depression and dissipate stress. It’s a common experience among endurance athletes and has been verified in clinical trials that have successfully used exercise to treat anxiety disorders and clinical depression. Exercise can also improve your sleep, which is often disrupted by stress, depression and anxiety. If athletes and patients can derive psychological benefits from exercise, so can you. The mental benefits of aerobic exercise have a neurochemical basis. Exercise promotes production of neurohormones like norepinephrine that are associated with improved cognitive function, elevated mood and learning. Exercise forces the body’s physiological systems — all of which are involved in the stress response — to communicate much more closely than usual resulting in improved communication which could be the basis of both greater reserves of the neurochemicals that help the brain communicate with the body and the body’s improved ability to respond to stress. Exercise also stimulates the production of endorphins, chemicals in the brain that are the body’s natural painkillers and mood elevators. Endorphins are responsible for the “runner’s high” and for the feelings of relaxation and optimism that accompany many hard workouts. Exercise is meditation in motion. By concentrating exclusively on the rhythm of your exercise, you experience many of the same benefits of meditation while working out. Focusing on a single physical task can produce a sense of energy and optimism, which can help provide calmness and clarity. After a fast-paced game of racquetball or several laps in the pool, you’ll often find that you’ve forgotten the day’s irritations and concentrated only on your body’s movements. As you begin to regularly shed your daily tensions through movement and physical activity, you may find that this focus on a single task, and the resulting energy and optimism, can help you remain calm and clear in everything you do. All of these exercise benefits can ease your stress levels and give you a sense of command over your body and your life. In other words, simple aerobic exercise like brisk walking and concentrating your mind on rhythm of walk would do all wonders of yoga.

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The moral of the story:

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1. Yoga is an ancient Hindu spiritual practice that synchronises adoption of specific bodily posture or series of postures with breath control & breathing exercise; leading to meditation & relaxation, ultimately resulting in attaining a state of consciousness unmixed with any other object. The goal of Yoga is Yoga, the union with the ultimate, that is to reach one’s true self without any distractions.

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2. Although yoga is a means of spiritual attainment for any and all seekers, irrespective of faith or no faith, its underlying principles are those of Hindu philosophy. Just as the practice of the Japanese martial arts of karate and aikido does not require becoming a Buddhist, the practice of yoga does not require you adopt Hinduism.

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3. There are 250 million estimated practitioners of yoga globally. Around 20.4 million Americans practise yoga. Many people who practice yoga do so to maintain their health and well-being, improve physical fitness, relieve stress, and enhance quality of life. In addition, they may be addressing specific health conditions such as back pain, depression and anxiety.

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4. Yoga was developed by men and practiced nearly exclusively by men for centuries.  It is only in recent times that so many women have flocked to the practice. In America, 70 to 80 % yoga practitioners are women.

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5. Yoga is not a physical system with a spiritual component but a spiritual system with a physical component. The mere fact that one might do a few stretches with the physical body does not in itself mean that one is doing real yoga. What has spread all over the world is not real yoga but merely a physical exercise.

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6. The biggest pitfall of yoga is finding a qualified teacher as yoga is not easy to learn, and yoga practice is physically, emotionally and mentally challenging. Yoga should be practiced carefully under the guidance of a qualified instructor to prevent yoga injury and to perform true yoga and not sham-yoga. The sham-yoga provides only exercise benefit to you akin to leisurely walking without stress reduction.

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7. There is scientific evidence to show that yoga benefits physical and mental health via down-regulation of hypothalamic–pituitary–adrenal (HPA) axis and sympathetic nervous system (SNS), and up-regulation of parasympathetic nervous system (PNS); all resulting in down-regulating stress response.

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8. Aerobic exercise transiently increases heart rate, respiratory rate, blood pressure, oxygen consumption and metabolic rate while yoga asanas transiently decreases heart rate, respiratory rate, blood pressure, oxygen consumption and metabolic rate except fast paced yoga. Sympathetic nervous system dominates in aerobic exercise while parasympathetic nervous system dominates in yoga.

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9. Meta-analysis of 81 published studies to compare yoga versus aerobic exercise revealed that yoga is especially beneficial for combating stress that is a direct result of a fast paced modern lifestyle. Over the last 100 years, our lives have become very fast paced: cell phones, traffic snarls, computers & internet, television, relationship demands, strong work ethic, meeting deadlines, etc. often results in people experiencing a lot of stress. Consequently, there is a strong need to de-stress to calm our minds. Remember stress itself magnifies all the risk factors for heart disease.

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10. A study on breast cancer showed an increase in telomere length after participating in a weekly hatha yoga & mindful meditation program as well as clinical psychotherapy for 12 weeks. In other words, yoga and psychotherapy are comparable in lengthening telomeres. Cancer cells have an enzyme called telomerase which maintains telomere length preventing telomere shortening so that they can replicate for ever. While lengthened telomeres are helpful to prevent aging and degenerative disorders, lengthened telomeres would worsen cancer. Many studies found yoga improving psychological health i.e. improved sleep, improved mood, reduced stress and increased acceptance of the condition in cancer patients comparable to psychotherapy of cancer patients which reduces depression, reduces anxiety, improves sleep and works as a coping mechanism. In other words, it makes no difference whether cancer patients practice yoga or undergo psychotherapy.

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11. Yoga is recommended for depression although it is less effective than antidepressants and electroconvulsive therapy. A randomised controlled magnetic resonance spectroscopy (MRS) scan study found that yoga increased thalamic GABA levels associated with improved mood and decreased anxiety.

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12. Yoga is recommended as an additional therapy to chronic low back pain.

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13. Yoga is not recommended for asthma, epilepsy and schizophrenia.

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14. The benefits yoga provides to patients suffering from hypertension and diabetes mellitus is akin to benefits they get by other forms of physical exercise (e.g. walking) and dietary modifications.

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15. There is weak evidence to recommend yoga to elderly to improve balance and stability, not to forget increased risk of fractures in elderly with osteoporosis.

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16. Yoga is widely used by patients with a variety of rheumatic diseases but there is no credible evidence to show improvement in any rheumatic disease. However yoga is a useful supplementary approach to reduce pain.

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17. Nasal irrigation with hypertonic saline (as done in Jala Neti) is a proven and effective modality of treatment in Rhino-sinusitis by improving mucociliary clearance, thinning of mucus, and decreasing inflammation.

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18. Yoga burns 2 to 3 calories per minute similar to walking leisurely, therefore unlikely to promote weight loss in obese individuals. However, yoga reduces stress and cortisol level thereby reduce food intake and yoga promotes mindful eating reducing intake of unhealthy foods (e.g. junk food). All these may promote weight reduction.

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19. A large meta-analysis of 37 RCTs found that there is no difference between yoga and aerobic exercise as far as blood pressure reduction, lipid optimization and weight reduction. As a corollary, yoga could be as effective as cycling or brisk walking in reducing the risk of a heart attack or stroke. Two other ancient practices that join slow, flowing motions with deep breathing — tai chi and qigong — seem to offer similar advantages. However to perform true yoga, you need qualified yoga teacher and it is not easy to learn and practice yoga. On the other hand, brisk walking is easy; need no teacher and no learning. I recommend brisk walking to everybody to reduce risk of heart attack and stroke. Remember not to walk on streets with traffic to avoid road traffic accident. Those with musculoskeletal or joint problems or elderly may choose yoga over brisk walking.

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20. Yoga is not contraindicated in pregnancy but only some yoga poses and breathing practices are allowed.

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21. People who practice yoga are generally young, healthy, educated, belonging to higher socio-economic strata of society, eating healthy diet, leading disciplined life and less likely to indulge in alcoholism/smoking. All these are confounding variables which directly affect results of yoga studies. In other words, so called health benefits of yoga could be due to these confounding variables.

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22. The scientific study of yoga requires rigorous methodology.  Much of the research on yoga has taken the form of preliminary studies or clinical trials of low methodological quality, including small sample sizes, inadequate blinding, lack of randomization, and high risk of bias. The quality of evidence is generally low. It is impossible to “treat” a group of yoga subjects and avoid placebo effect, since yoga practitioners are aware of the fact that they are doing yoga.  The “treatment” under study should be consistent and similar each time it is administered, in order to control variability, which could skew results. As many yoga participants and teachers know, several variables can affect a yoga practice. For instance, most studies involving yoga do not enumerate the poses that were utilized, how long they were held or which style of yoga was emphasized. This makes reproducing results impossible. Significant heterogeneity and variability in reporting interventions by type of yoga, settings, and population characteristics limit the generalizability of results. In other words, to be honest, most yoga studies are inherently fallible.

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23. Majority of systemic reviews criticize the methodology of yoga research and find that yoga has little or no effect on serious illness. That doesn’t mean you shouldn’t do yoga. By all means do yoga if it bring you contentment and stress reduction, and as a preferred form of exercise.

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24. Yoga hype is created by media and scientific evidence of yoga inefficacy is buried by media.

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25. When it comes to practicing yoga it’s not “one size fits all”. Everyone’s body is different, and yoga postures should be modified by yoga teacher based on individual’s ability. The reasons for yoga injuries are beginners’ competitiveness & over-enthusiasm (improper practice), and instructors’ lack of qualification (inexperienced teacher). Although these reasons are certainly true, another reason for yoga injuries is that the human body is not designed to be in the right angle poses that make up a huge percentage of modern yoga asana practice. Many yoga injuries are caused by putting the body in positions that are unnatural.

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26. Parents should be wary of yoga guru when they send their daughter for yoga classes. There is evidence to show that some modern yoga gurus are sexual predators and they coerce girls/women to have sex with them under disguise of promoting spiritual development.

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27. I challenge the basic axiom of yoga that the breath gives us a tool with which we can explore the subtler structures of our mental and emotional worlds. The job of lungs is to provide oxygen and remove carbon dioxide. Lungs have no relationship with mind functioning. Our daily breathing is subconscious, that is we are unaware of it. What yoga does is to make you aware of your breathing and bring your mind concentration on breath consequently removing distractions leading to de-stress. Conscious breathing would shift focus from stressors and thereby reduce stress.  Nadiis, Chakras and Prana do not exist.

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28. Yoga meditation is concentrative and different from mindfulness meditation. Both yoga (i.e. with asanas and pranayama) and non-yoga meditation (e.g. mindfulness practice) alter brain plasticity by increasing grey matter in hippocampus and reducing grey matter in amygdala to reduce stress and anxiety. Both yoga and non-yoga meditation showed much less decline in fluid intelligence with age resulting in improved mental health. Both yoga and non-yoga meditation causes relaxation to switch on disease-fighting genes. So the issue is true meditation and true relaxation no matter whether you achieve it through yoga or other means. Different kinds of meditation & relaxation practices have existed in different civilizations all leading to stress reduction.

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29. Yoga cannot be considered as cardio because most yoga asanas reduce heart rate and even fast paced ashtanga power yoga raises heart rate to an average of 95 beats per minute, and therefore enhancement of strength of heart by doing cardio cannot be achieved by yoga. However, yoga has same benefits of aerobic exercise because besides muscle stretching and isometric exercise, yoga reduces stress. Although it sounds contradictory, aerobic exercise itself reduces mental stress by releasing endorphins; and by concentrating exclusively on the rhythm of your exercise, you experience many of the same benefits of meditation while working out. In other words, simple aerobic exercise like brisk walking and concentrating your mind on rhythm of walk would do all wonders of yoga.

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Dr. Rajiv Desai. MD.

July 20, 2015

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Postscript:

I have never done yoga in my life, no asana and no pranayama. Nonetheless I am in good health and clear mind. Patanjali’s Yoga supports duality. You can reach your true self by either having faith in God or even without God. Patanjali says God is one of the many ways to reach the ultimate but it is not necessary to believe in God to reach your destination. Patanjali’s concept of duality and my theory of ‘Duality of Existence’ have something in common, the concept of duality.

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Footnote:

Please read my article “Stress” posted in November 2011 on this website. Experts tell us that stress, in moderate doses, is necessary in our life. Stress is part of life in a fast-paced society. However, contrary to popular belief, stress is not always bad. We need some stress to stimulate us. A certain level of stress is beneficial. This type of stress is called eustress. It helps us to set and achieve goals as well as perform at a higher level. However, there are times when stress is overwhelming. This type of stress—called distress—paralyses rather than stimulates. It contributes to decreased health and well-being. In fact, stress is a factor in 11 of the top 15 causes of death in Canada and is a significant reason for physician visits. Therefore, an important part of healthy living is to learn to bring stress to beneficial levels. When I use the term ‘stress’ in the article ‘Yoga’, I mean distress. What yoga does is to reduce distress to eustress level. Aerobic exercise is stressful but that is eustress which brings numerous health benefits.

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NET NEUTRALITY

June 15th, 2015

NET NEUTRALITY:

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I am reminded of Abraham Lincoln’s remark: “The world has never had a good definition of the word liberty. We all declare for liberty, but in using the same word we do not mean the same thing.”  Substitute ‘net neutrality’ for ‘liberty’, and that’s where we are today. The Internet has unleashed innovation, enabled growth, and inspired freedom more rapidly and extensively than any other technological advance in human history. Its independence is its power. Net neutrality means internet service providers (ISPs) should treat all data on internet equally. The ISPs have structural capacity to determine the way in which information is transmitted over the internet and the speed at which it is delivered.  And the present internet network operators, principally large telephone and cable companies—have an economic incentive to extend their control over the physical infrastructure of the internet to leverage their control of internet content.  If they went about it in the wrong way, these companies could institute changes that have the effect of limiting the free flow of information over the internet in a number of troubling ways. Network operators could prioritize the transmission of some content—their own for example—over other material produced by competitors. If this was to be allowed, web companies would lose revenues that they could otherwise devote to improvements in old products and innovations in new ones. Worse yet, the smaller content providers, who can now capitalize on the two-way nature of the internet—whether online stores or forums for democratic discourse—might be unable to secure quality service online.  An entrepreneur’s fledgling company should have the same chance to succeed as established corporations, and that access to a high school student’s blog shouldn’t be unfairly slowed down to make way for advertisers with more money. At the core of the principle of net neutrality is thus the idea that all content on the internet should be accessible in a fully equitable way and once an internet user has accessed that content, he should be able to engage with that content in the same way that he would engage with any other content on the internet. Allowing broadband carriers to control what people see and do online would fundamentally undermine the principles that have made internet such a success. On the other hand, to be honest, there is no absolute neutrality. The world is neither neutral nor equal. Umpires in a game of cricket were perceived to be biased and so we have neutral umpires from countries not playing the present game. Humans have been subjective. They’ve got their own positions, opinions and priorities. So net neutrality cannot be seen in isolation of entire gambit of human behaviours but approached by combining different views and opinions.

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Internet terminology, abbreviations and synonyms:

Internet Backbone:

The collection of cables and data canters that make up the core of the internet. This is operated not by a single operator but by many independent companies spread across the globe.

Internet Service Provider (ISP):

A company, such as Comcast or Verizon or Airtel or Tata docomo, that plugs into the backbone and then provides internet connections to homes and businesses. ISP is also known as TSP (telecom service provider) or Telco or broadband carriers or network operators or internet access providers or platform operator. An ISP provides internet services to users via cable or wireless connections.

Access ISP = last mile ISP = eyeball ISP = ISP that provides internet access to user.

Content Provider:

Companies such as Google, Facebook, and Netflix that provide the webpages, videos, and other content that moves across the internet. My website  www.drrajivdesaimd.com   is also a content provider. A content provider is anyone who has a website that delivers content to internet users. Content and service providers (CSPs) offer a wide range of applications and content to the mass of potential consumers.

Peering:

Where one internet operation connects directly to another so that they can trade traffic. This could be a connection between an ISP such as Comcast and an internet backbone provider such as Level 3. But it could also be a direct connection between an ISP and a content provider such as Google.

Content Delivery Network (CDN):

A network of computer servers set up inside an ISP that delivers popular photos, videos, and other content. These servers can deliver this content faster to home users because they’re closer to home users. Companies such as Akamai and Cloudflare run CDNs that anyone can use. But content providers such as Google and Netflix now run their own, private CDNs as well.

Regulator:

FCC (federal communication commission of U.S.) and TRAI (telecom regulatory authority of India) are some examples of regulators that regulate ISPs.

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ISP = internet service provider

CSP = content & service provider

IU = internet user = user = consumer

NN = net neutrality

IP = internet protocol

TCP = transmission control protocol

VoIP = voice over internet protocol

Kbps = kilobits per second

Mbps = megabits per second = 1000 Kbps

Gbps = gigabits per second = 1000 Mbps

QoS = quality of service

CDN = content delivery network

P2P = peer-to-peer file sharing

SMS = short message service

MMS = multimedia message service

OTT = over the top services

BE = best effort

LAN = local area network

WAN = wide area network

WLAN = wireless local area network

DSL = digital subscriber line

Packets = datagrams

IPTV = internet protocol television

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Who’s an Internet user?

A user is a pretty broad term to describe someone who uses the Internet so let’s take a closer look at what “user” means. A user can be a person, small business, local city, state or national government agency, or a large organization, such as the U.S. Government, AT&T, Google, Microsoft, or Facebook. As you can see by this wide range of Internet users, an organization that makes laws, sets tariffs, owns portions of the cables that makeup the Internet, or has the money to buy faster speeds and pay for larger amounts of data could obtain an advantage over a smaller organization or user. In addition to size, governments of certain countries restrict both who is allowed to use the Internet and what the users can do when using the Internet. Some countries have tightly controlled Internets within their borders, and net neutrality is sometimes used more broadly to include the freedom to send and receive data without government restrictions.

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The figure below depicts how internet works today. To understand net neutrality and how ISPs interfere to circumvent net neutrality, this figure must be memorised:

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There are a lot of emotional terms used to describe various aspects of what makes the melting pot of the neutrality debate. For example, censorship or black-holing (where route filtering, fire-walling and port blocking might say what is happening in less insightful way); free-riding is often bandied about to describe the business of making money on the net (rather than overlay service provision); monopolistic tendencies, instead of the natural inclination of an organisation that owns a lot of kit that they’ve sunk capital into, to want to make revenue from it!

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Growth of internet:

As the flood of data across the internet continues to increase, there are those that say sometime soon it is going to collapse under its own weight. Back in the early 90s, those of us that were online were just sending text e-mails of a few bytes each, traffic across the main US data lines was estimated at a few terabytes a month, steadily doubling every year. But the mid 90s saw the arrival of picture rich websites, and the invention of the MP3. Suddenly each net user wanted megabytes of pictures and music, and the monthly traffic figure exploded. For the next few years we saw more steady growth with traffic again roughly doubling every year. But since 2003, we have seen another change in the way we use the net. The YouTube generation want to stream video, and download gigabytes of data in one go. In one day, YouTube sends data equivalent to 75 billion e-mails; so it’s clearly very different. The network is growing up, is starting to get more capacity than it ever had, but it is a challenge. Video is real-time; it needs to not have mistakes or errors. E-mail can be a little slow. You wouldn’t notice if it was 11 seconds rather than 10, but you would notice that on a video.

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Introduction to net neutrality:

The Internet owes much of its success to the fact that it is open and easily accessible, provided that the user has an Internet connection. Any content provider who has opportunity to test its ideas and their relative value in the marketplace can put its content on internet. The required investment, such as buying a domain name, renting a space on a server and implementing its application or software has been relatively low. As a result, new services have been made available to consumers: browsing, mailing, Peer-to-Peer (P2P), instant messaging, Internet telephony (Voice over Internet Protocol ‘VoIP’), videoconference, gaming online, video streaming, etc. This development has taken place mainly on a commercial basis without any regulatory intervention.

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Net neutrality is the principle that all data on the internet is equal, and must be treated equally with no discrimination on the basis of content, user or design by governments and Internet Service Providers (ISP’s). Net Neutrality is the principle that all data on the internet is transported using best effort. This includes not discriminating for origin and service. Under this principle, consumers can make their own choices about what applications and services to use and are free to decide what lawful content they want to access, create, or share with others… Once you’re online, you don’t have to ask permission or pay tolls to broadband providers to reach others on the network. If you develop an innovative new website, you don’t have to get permission to share it with the world. For example, Times is a widely popular online newspaper, while Mirror has comparatively fewer visitors to their website. Right now, if Mirror wanted to boost their page views, they would have to write more engaging stories and find ways to share their content so that more people read it. They are not allowed to make deals with ISP’s to charge customers less money if they visit Mirror website. Net Neutrality means that Internet Service Providers should bill you on the amount of bandwidth you have consumed, and not on which website you visited. Net neutrality is the principle that all packets of data over the internet should be transmitted equally, without discrimination. So, for example, net neutrality ensures that my blog can be accessed just as quickly as, say the BBC website. Essentially, it prevents ISPs from discriminating between sites, organisations etc. whereby those with the deepest pockets can pay to get in the fast lane, whilst the rest have to contend with the slow lane. Instead, every website is treated equally, preventing the big names from delivering their data faster than a small independent online service. This ensures that no one organisation can deliver their data any quicker than anyone else, enabling a fair and open playing field that encourages innovation and diversity in the range of information material online. The principles of net neutrality are effectively the reason why we have a (reasonably) diverse online space that enables anyone to create a website and reach a large volume of people. Network neutrality is the idea that Internet service providers must allow customers equal access to content and applications regardless of the source or nature of the content. Presently the Internet is indeed neutral: All Internet traffic is treated equally on a first‐come, first‐serve basis by Internet backbone owners. The Internet is neutral because it was built on phone lines, which are subject to ‘common carriage’ laws. These laws require phone companies to treat all calls and customers equally. They cannot offer extra benefits to customers willing to pay higher premiums for faster or clearer calls, a model knows as tiered service.

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Net neutrality is not a new concept relative to the age of the Internet; its roots are embedded within the founders.  Net Neutrality refers to a guiding principle that preserves the free and open Internet with no discrimination.  It makes it such that an Internet Service Provider (ISP) cannot discriminate the speed of the connection – or lack thereof – to one content provider versus another (Eudes 2008). When the Internet was first invented, founders wanted to be sure that it was to provide a safe haven for the transportation of information without any biases. They wanted to ensure that all people had a consistent way to use the Internet; regardless of their connection and social status (Margulius, 2003). Net Neutrality has two polarizing factions; those who are in favor, and those who are not. On this topic there is not a middle ground. Those who are in favor of Net Neutrality consist of organizations like Microsoft, Google, and other content providers.  Those who are against Net Neutrality are generally made of telecommunication network organizations and/or ISPs (Owen 2007).  Network neutrality, or open inter-working, means in accessing the World Wide Web, one is in full control over how to go online, where to go and what to do, as long as these are lawful. So firms that provide Internet services should treat all lawful Internet content in a neutral manner. It also required such companies not to charge users, content, platform, site, application or mode of communication differentially. These are also the founding principles of the Internet and what has made it the largest and most diverse platform for expression in recent history.

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Net neutrality is when an ISP treats all content on the internet neutrally, and does not prioritize one over the other. ISPs are charging content companies because money makes their shareholders happy. Also because they believe they have the right to do so when a certain content provider (e.g. netflix) takes up the majority of the bandwidth from their data centers. Companies are concerned because it will give ISPs free reign to downright slow down any content they please and demand money to bring it to normal speed. Whether you’re accessing How-To Geek, Google, or a tiny website running on shared hosting somewhere, your Internet service provider treats these connections equally and forwards the data along without prioritizing any one party. Your Internet service provider could prioritize data from Google, charging them for the privilege. They could throttle Netflix while providing you with unlimited bandwidth to stream videos from their own video-streaming service. They could restrict the bandwidth available to VoIP applications and encourage you to keep paying for a phone line. They could throttle connections to websites run by startups and other individuals that haven’t signed a contract with the Internet service provider to pay for priority access. These actions would all be violations of net neutrality. However, by and large, Internet service providers don’t violate net neutrality in this way. They just forward packets along — that’s the way the Internet has worked and it has given us the Internet we have today.

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The figure below shows how ISPs would like the internet to be without net neutrality:

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One percent of the world’s population controls almost 50 percent of the world’s wealth, according to the poverty eradication nonprofit Oxfam. Advocates of net neutrality worry that loosening the rules for ISPs will result in a one-percent version of the Internet. Here’s how it could happen. In 2004, Internet traffic was more or less equally distributed across thousands of Web companies. Just 10 years later, half of all Internet traffic originated from only 30 companies. The top three websites by daily unique visitors and page views are Google, Facebook and YouTube. In terms of data, Netflix and YouTube hog more than half of all downstream traffic in North America. That means one out of every two bytes of data traveling across the Internet is streaming video from Netflix or YouTube. If the distribution of Internet traffic is so out of whack now, imagine what it would be like if ISPs were given the green light to give further preferential treatment to the biggest players. Would there be any bandwidth left for the 99 percent — independent video producers, upstart social media sites, bloggers and podcasters? This is a really important reason why you should care about net neutrality. The Internet, as it exists today, is an open forum for free speech and freedom of expression. Websites publishing both popular and unpopular viewpoints are treated equally in terms of how their data gets from servers to screens. If the FCC allows Internet service providers (ISPs) to charge extra money for access to Internet last-mile fast lanes, the playing field of free speech is no longer equal. Those with the money to pay for special treatment could broadcast their opinions more quickly and more smoothly than their opponents. Those without as many resources — activists, artists and political outsiders — could be relegated to the Internet slow lane.

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If you’re lucky enough to live in a country that doesn’t regulate the information you access online, you probably take net neutrality for granted. You search the Web unrestricted by government censors, free to choose what information to believe or discard, and what websites and online services to patronize. In mainland China, citizens of the highly restrictive communist regime enjoy no such freedoms. This is what a heavily censored and closely monitored Internet looks like:

1. Chinese internet service providers (ISPs) block access to a long list of sites banned by the government.

2. Specific search terms are red flagged; type them into Google and you’ll be blocked from the search engine for 90 seconds.

3. Chinese ISPs are given lists of problematic keywords and ordered to take down pages that include those words.

4. The government and private companies employ 100,000 people to police the Internet and snitch on dissenters.

5. The government also pays people to post pro-government messages on social networks, blogs and message boards.

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The unequal Web:

The figure above shows that richer countries rank highest for net access, freedom and openness. The web is becoming less free and more unequal, according to a report from the World Wide Web Foundation. Its annual web index suggests web users are at increasing risk of government surveillance, with laws preventing mass snooping weak or non-existent in over 84% of countries. It also indicates that online censorship is on the rise. The report led web inventor Sir Tim Berners-Lee to call for net access to be recognised as a human right. That means guaranteeing affordable access for all, ensuring internet packets are delivered without commercial or political discrimination, and protecting the privacy and freedom of web users regardless of where they live.

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Net neutrality worldwide:

This map shows data from Glasnost, one of the measurement lab tools for examining your internet connection. Authors map the percentage of tests where violations of net neutrality was discovered worldwide. Data covers the period from 2012-12-26 00:02:11 to 2013-12-22 23:59:19.

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Outline of computer, internet, bits, bytes, speed, packets and internet protocol:

Computer is defined as a programmable machine that computes (stores, processes and retrieves) information (data) according to a set of instructions (program). Computer processes data in numerical form and its digital electronic circuits perform mathematical operations using Binary System. Binary system means using only two digits for arithmetic processing, namely, 0 and 1 known as bits (binary digits).

0 means absence of current/voltage in electronic circuit = off

1 means presence of current/voltage in electronic circuit = on

A series of 8 consecutive bits is known as a byte which permits 256 different on/off combinations.

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Computers see everything in terms of binary. In binary systems, everything is described using two values or states: on or off, true or false, yes or no, 1 or 0. A light switch could be regarded as a binary system, since it is always either on or off. As complex as they may seem, on a conceptual level computers are nothing more than boxes full of millions of “light switches.” Each of the switches in a computer is called a bit, short for binary digit. A computer can turn each bit either on or off. Your computer likes to describe on as 1 and off as 0. By itself, a single bit is kind of useless, as it can only represent one of two things. By arranging bits in groups, the computer is able to describe more complex ideas than just on or off. The most common arrangement of bits in a group is called a byte, which is a group of eight bits.

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Internet is defined as a global communication system of data connectivity between computers using transmission control protocol (TCP) and internet protocol (IP) to serve billions of users in the world. Internet is the greatest invention in communication breaking barriers of age/distance/language/religion/race/region and making the world a better place to live in. If you do not have internet access in 21′st century, you are illiterate. Internet scores over media due to internet’s openness and neutrality. Every school must teach basics of computer and internet to students.

Data transfer rate (speed) of internet is usually in bits per second.

1000 bits per second = 1 kilobit per second (Kbps)

1000000 bits per second = 1 megabit per second (Mbps) = 1000 Kbps

Broadband means download internet speed of more than 4 Mbps and upload internet speed of more than 1 Mbps. Newer technology with fiber-optic cables can give internet speed of 100 Mbps.

The speed of travel of data from computer to computer through wireless technology (air) is same as the speed of radio waves (speed of light) which is 300,000 kilo meters per second. The speed of travel of data from computer to computer through wired network is same of speed of electricity which is also near speed of light. Please do not confuse between speed of data travel i.e. speed of light and internet speed i.e. data transfer rate in Kbps or Mbps which refers to the speed of  digital data converted into radio waves or electricity and not the speed of data when traveling through the air or wires. Data transfer rate and data travel rate are different. The term latency is used to determine amount of time taken by packets to travel from source to destination. Since speed of light is constant and fastest, latency depends on time taken by packets to travel through routers (queuing) and other hardware/software.

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IP address:

The picture below illustrates two computers connected to the Internet; your computer with IP address 1.2.3.4 and another computer with IP address 5.6.7.8. The Internet is represented as an abstract object in-between.

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An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.  An IP address serves two principal functions: host or network interface identification and location addressing. A name indicates what we seek. An address indicates where it is. A route indicates how to get there. The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, because of the growth of the Internet and the predicted depletion of available addresses, a new version of IP (IPv6), using 128 bits for the address, was developed in 1995. IP addresses are usually written and displayed in human-readable notations, such as 172.16.254.1 (IPv4), and 2001:db8:0:1234:0:567:8:1 (IPv6). Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations. There are about 4.3 billion IP addresses. The class-based, legacy addressing scheme places heavy restrictions on the distribution of these addresses. TCP/IP networks are inherently router-based, and it takes much less overhead to keep track of a few networks than millions of them. The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the addressing capability in the Internet. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This new generation of the Internet Protocol, intended to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6 (IPv6) in 1995.  The address size was increased from 32 to 128 bits or 16 octets. This, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2128, or about 3.403×1038 addresses. The Domain Name System (DNS) converts IP addresses to domain names so that users only need to specify a domain name to access a computer on the Internet instead of typing the numeric IP address.  DNS servers maintain a database containing IP addresses mapped to their corresponding domain names.

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IP address assignment:

Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a static IP address. In contrast, in situations when the computer’s IP address is assigned newly each time, this is known as using a dynamic IP address. An Internet Service Provider (ISP) will generally assign either a static IP address (always the same) or a dynamic address (changes every time one logs on). If you connect to the Internet from a local area network (LAN) your computer might have a permanent IP address or it might obtain a temporary one from a DHCP (Dynamic Host Configuration Protocol) server. In any case, if you are connected to the Internet, your computer has a unique IP address.

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Packets and protocols:

When a file is sent from one computer to another, it is broken into small pieces called packets. A typical packet contains perhaps 1,000 or 1,500 bytes. It turns out that everything you do on the Internet involves packets. For example, every Web page that you receive comes as a series of packets, and every e-mail you send leaves as a series of packets. The packets are labelled individually with origin, destination and place in the original file. The packets are sent sequentially over network. Each packet carries the information that will help it get to its destination — the sender’s IP address, the intended receiver’s IP address, something that tells the network how many packets this e-mail message has been broken into and the number of this particular packet. When a packet get on a router, the router looks at the packet to see where it needs to go. The routers determine where to send information from one computer to another. Routers are specialized computers that send your messages and those of every other Internet user speeding to their destinations along thousands of pathways. The packets carry the data in the protocols that the Internet uses: Transmission Control Protocol/Internet Protocol (TCP/IP). Using “pure” IP, a computer first breaks down the message to be sent into small packets, each labelled with the address of the destination machine; the computer then passes those packets along to the next connected Internet machine (router), which looks at the destination address and then passes it along to the next connected internet machine, which looks the destination address and pass it along, and so forth, until the packets (we hope) reach the destination machine. IP is thus a “best efforts” communication service, meaning that it does its best to deliver the sender’s packets to the intended destination, but it cannot make any guarantees. If, for some reason, one of the intermediate computers “drops” (i.e., deletes) some of the packets, the dropped packets will not reach the destination and the sending computer will not know whether or why they were dropped. By itself, IP can’t ensure that the packets arrived in the correct order, or even that they arrived at all. That’s the job of another protocol: TCP (Transmission Control Protocol). TCP sits “on top” of IP and ensures that all the packets sent from one machine to another are received and assembled in the correct order. Should any of the packets get dropped during transmission, the destination machine uses TCP to request that the sending machine resend the lost packets, and to acknowledge them when they arrive. TCP’s job is to make sure that transmissions get received in full, and to notify the sender that everything arrived OK. Each packet is sent off to its destination by the best available route — a route that might be taken by all the other packets in the message or by none of the other packets in the message. This makes the network more efficient. First, the network can balance the load across various pieces of equipment on a millisecond-by-millisecond basis. Second, if there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message. Packets don’t necessarily all take the same path — they’ll generally travel the path of least resistance. That’s an important feature. Because packets can travel multiple paths to get to their destination, it’s possible for information to route around congested areas on the Internet. In fact, as long as some connections remain, entire sections of the Internet could go down and information could still travel from one section to another — though it might take longer than normal. When the packets get to you, your device arranges them according to the rules of the protocols. It’s kind of like putting together a jigsaw puzzle. When you send an e-mail, it gets broken into packets before zooming across the Internet. Phone calls over the Internet also convert conversations into packets using the Voice over Internet protocol (VoIP).

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Many things can happen to packets as they travel from origin to destination, resulting in the following problems as seen from the point of view of the sender and receiver:

Low throughput:

Due to varying load from disparate users sharing the same network resources, the bit rate (the maximum throughput) that can be provided to a certain data stream may be too low for realtime multimedia services if all data streams get the same scheduling priority.

Dropped packets:

The routers might fail to deliver (drop) some packets if their data loads are corrupted, or the packets arrive when the router buffers are already full. The receiving application may ask for this information to be retransmitted, possibly causing severe delays in the overall transmission.

Errors:

Sometimes packets are corrupted due to bit errors caused by noise and interference, especially in wireless communications and long copper wires. The receiver has to detect this and, just as if the packet was dropped, may ask for this information to be retransmitted.

Latency:

Latency is defined as the time it takes for a source to send a packet of data to a receiver. Latency is typically measured in milliseconds. The lower the latency (the fewer the milliseconds), the better the network performance. It might take a long time for each packet to reach its destination, because it gets held up in long queues, or it takes a less direct route to avoid congestion. This is different from throughput, as the delay can build up over time, even if the throughput is almost normal. In some cases, excessive latency can render an application such as VoIP or online gaming unusable. Ideally latency is as close to zero as possible.

Jitter:

Packets from the source will reach the destination with different delays. A packet’s delay varies with its position in the queues of the routers along the path between source and destination and this position can vary unpredictably. This variation in delay is known as jitter and can seriously affect the quality of streaming audio and/or video.

Out-of-order delivery:

When a collection of related packets is routed through a network, different packets may take different routes, each resulting in a different delay. The result is that the packets arrive in a different order than they were sent. This problem requires special additional protocols responsible for rearranging out-of-order packets to an isochronous state once they reach their destination. This is especially important for video and VoIP streams where quality is dramatically affected by both latency and lack of sequence.

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Protocols:

At their most basic level, protocols establish the rules for how information passes through the Internet. Protocols are to computers what language is to humans. Since this article is in English, to understand it you must be able to read English. Similarly, for two devices on a network to successfully communicate, they must both understand the same protocols. Without these rules, you would need direct connections to other computers to access the information they hold. You’d also need both your computer and the target computer to understand a common language. When you want to send a message or retrieve information from another computer, the TCP/IP protocols are what make the transmission possible. You’ve probably heard of several protocols on the Internet. For example, hypertext transfer protocol (HTTP) is what we use to view Web sites through a browser — that’s what the http at the front of any Web address stands for. If you’ve ever used an FTP server, you relied on the file transfer protocol. Protocols like these and dozens more create the framework within which all devices must operate to be part of the Internet.

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Protocol Stacks:

So your computer is connected to the Internet and has a unique address. How does it ‘talk’ to other computers connected to the Internet? An example should serve here: Let’s say your IP address is 1.2.3.4 and you want to send a message to the computer 5.6.7.8. The message you want to send is “Hello computer 5.6.7.8!”  Obviously, the message must be transmitted over whatever kind of wire connects your computer to the Internet. Let’s say you’ve dialled into your ISP from home and the message must be transmitted over the phone line. Therefore the message must be translated from alphabetic text into electronic signals, transmitted over the Internet, then translated back into alphabetic text. How is this accomplished? Through the use of a protocol stack. Every computer needs one to communicate on the Internet and it is usually built into the computer’s operating system (i.e. Windows, Unix, etc.). The protocol stack used on the Internet is referred to as the TCP/IP protocol stack because of the two major communication protocols used. The TCP/IP stack looks like this:

Protocol Layer Comments
Application Protocols Layer Protocols specific to applications such as WWW, e-mail, FTP, etc.
Transmission Control Protocol Layer TCP directs packets to a specific application on a computer using a port number.
Internet Protocol Layer IP directs packets to a specific computer using an IP address.
Hardware Layer Converts binary packet data to network signals and back.
(E.g. Ethernet network card, modem for phone lines, etc.)

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If we were to follow the path that the message “Hello computer 5.6.7.8!” took from our computer to the computer with IP address 5.6.7.8, it would happen something like this:

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Internet layers/protocol layers:

The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport datagrams (packets) from the originating host across network boundaries to the destination host specified by a network address (IP address) which is defined for this purpose by the Internet Protocol (IP). A common design aspect in the internet layer is the robustness principle: ‘Be liberal in what you accept, and conservative in what you send’ as a misbehaving host can deny Internet service to many other users. The internet layer of the TCP/IP model is often compared directly with the network layer (layer 3) in the Open Systems Interconnection (OSI) protocol stack. OSI’s network layer is a catch-all layer for all protocols that facilitate network functionality. The internet layer, on the other hand, is specifically a suite of protocols that facilitate internetworking using the Internet Protocol.  Protocol layers exist to reduce design complexity and improve portability and support for change. Networks are organised as series of layers or levels each built on the one below. The purpose of each layer is to offer services required by higher levels and to shield higher layers from the implementation details of lower layers.

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OSI Reference Model:

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OSI consists of 7 layers of protocols, i.e., of 7 different areas in which the protocols operate. In principle, the areas are distinct and of increasing generality; in practice, the boundaries between the layers are not always sharp. The model draws a clear distinction between a service, something that an application program or a higher-level protocol uses, and the protocols themselves, which are sets of rules for providing services.

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The OSI Model was developed to help provide a better understanding of how a network operates. The better you understand the model the better you will understand networking.  It is composed of seven OSI layers.  Each layer is unique and supports the creation and control of data packets. The layers start with Physical and ends with the Application.  The first three layers relate to network equipment.  For example, switches are layer 2 devices and routers are layer 3 devices.

1. The first layer is the Physical layer and is where the data is either put onto the media or taken off the media. The media could be the network cable or wireless.  The data is in the form of bits and is called Bits as the PDU (protocol data unit). These bits can be voltage levels that represent binary numbers of 1 or 0.  They could also be light pulses traveling on a fiber optic cable or radio wave pulses for a wireless network.

2. The second layer is the Data Link layer and is where framing of the data takes place. The Frame is the PDU name at this layer.  The MAC (media access control) physical address is added or removed depending on which direction the data is traveling.  The MAC address is used by switches to switch the data to the appropriate computer or node that it is intended for in a LAN (local area network).

3. The third layer is the Network layer and is where the IP (internet protocol) address is added or removed and the PDU at this layer is called a Packet.  Routers operate at this level and use the IP (logical address) to route the data to the appropriate network. Network locations are found by the routers using routing tables to locate the appropriate networks.

4. The fourth layer is the Transport layer and is where the data is segmented (broken into pieces) and used by the TCP protocol to ensure accurate and reliable data is transferred. The data segments are numbers so that proper sequencing can be determined on the receiving side in order to rebuild accurate files. The PDU name at this layer is called Segment.

5. The fifth layer is the Session layer and is where the session is created, maintained, and torn-down when finished.

6. The sixth layer is the Presentation layer and is where the data is formatted or decrypted into files that the user can understand.

7. The seventh layer is the Application layer and is the user interface to the network where that data is either being generated or received.

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The Internet, like any other computer network, is defined in terms of layers; these are the often-referenced “OSI Layers”. This division into layers is a logical (rather than physical) one; the data traversing the network is eventually one long series of bits — 0′s and 1′s. Such “layers” is how we address the representation of those many bits; their grouping into clusters of bits that have meaning. The different network layers are different levels of interpretation of this large set of bits moving along the wire. Understanding the same raw traffic at different layers allows us to bridge the semantic gap between a bunch of 0′s and 1′s and an e-mail being sent or to a web site being browsed. After all, all emails and browsing sessions end up as 0′s and 1′s on a wire. Processing those sequences of bits at different layers of abstraction is what makes the network as versatile as it is and technically manageable. In a nutshell, Internet traffic is interpreted at seven layers, where each layer introduces meaningful data objects and uses the underlying layer to transfer these objects. Each of the many components of the Internet (applications sending and receiving data, routers, modems, and wires) knows how to process data at its own layer and needs not be aware of what the data represents at higher layers or of how data is processed by the lower layers.

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Understanding the layered architecture of the Internet allows us to define net neutrality:

Network neutrality is the adherence to the paradigm that operation at a certain layer, by a network component (or provider) that is chartered for operating at that layer, is not influenced by interpretation of the processed data at higher layers. So network neutrality is an intended feature of the Internet. A component operating at a certain layer is not required to understand the data it processes at higher layers. The network card operating at Layer 2 does not need to know that it is sending an e-mail message (Layer 7). It only needs to know that it is sending a frame (Layer 2) with a certain opaque payload. Net-neutrality is thus built into the Internet. When expanding the notion of net neutrality from the purely technical domain to the service domain, we can define network neutrality as the adherence to the paradigm that operation of a service at a certain layer is not influenced by any data other than the data interpreted at that layer, and in accordance with the protocol specification for that layer. Therefore, a service provider is said to operate in net neutrality if it provides the service in a way what is strictly “by the book”, where “the book” is the specification of the network protocol it implements as its service. Its operation is network-neutral if it is not impacted by any other logic other than that of implementing the network layer protocol that it is chartered at implementing.

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Router:

So how do packets find their way across the Internet? Does every computer connected to the Internet know where the other computers are? Do packets simply get ‘broadcast’ to every computer on the Internet? The answer to both the preceding questions is ‘no’. No computer knows where any of the other computers are, and packets do not get sent to every computer. The information used to get packets to their destinations are contained in routing tables kept by each router connected to the Internet. Routers are packet switches. A router is usually connected between networks to route packets between them. Each router knows about its sub-networks and which IP addresses they use. The router usually doesn’t know what IP addresses are ‘above’ it. When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks its routing table. If the network containing the IP address is found, the packet is sent to that network. If the network containing the IP address is not found, then the router sends the packet on a default route, usually up the backbone hierarchy to the next router. Hopefully the next router will know where to send the packet. If it does not, again the packet is routed upwards until it reaches a NSP (network service provider) backbone. The routers connected to the NSP backbones hold the largest routing tables and here the packet will be routed to the correct backbone, where it will begin its journey ‘downward’ through smaller and smaller networks until it finds its destination.

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Modem vs. router:

A router is a device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect. While connecting to a router provides access to a local area network (LAN), it does not necessarily provide access to the Internet. In order for devices on the network to connect to the Internet, the router must be connected to a modem. While the router and modem are usually separate entities, in some cases, the modem and router may be combined into a single device. This type of hybrid device is sometimes offered by ISPs to simplify the setup process.

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Modem:

A modem (modulator-demodulator) is a device that modulates signals to encode digital information and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. A modem is a device that provides access to the Internet. The modem connects to your ISP. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data. Modems which use a mobile telephone system (GPRS, UMTS, HSPA, EVDO, WiMax, etc.), are known as mobile broadband modems (sometimes also called wireless modems). Wireless modems can be embedded inside a laptop or appliance, or be external to it. External wireless modems are connect cards, USB modems for mobile broadband and cellular routers. A connect card is a PC Card or ExpressCard which slides into a PCMCIA/PC card/ExpressCard slot on a computer. USB wireless modems use a USB port on the laptop instead of a PC card or ExpressCard slot. A USB modem used for mobile broadband Internet is also sometimes referred to as a dongle. A cellular router may have an external datacard (AirCard) that slides into it. Most cellular routers do allow such datacards or USB modems. Cellular routers may not be modems by definition, but they contain modems or allow modems to be slid into them. The difference between a cellular router and a wireless modem is that a cellular router normally allows multiple people to connect to it (since it can route data or support multipoint to multipoint connections), while a modem is designed for one connection. By connecting your modem to your router (instead of directly to a computer), all devices connected to the router can access the modem, and therefore, the Internet. The router provides a local IP address to each connected device, but they will all have the same external IP address, which is assigned by your ISP.

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The figure below shows request path and return path of internet utilizing modem, router and DNS server:

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In order to retrieve this article, your computer had to connect with the Web server containing the article’s file. We’ll use that as an example of how data travels across the Internet. First, you open your Web browser and connect to our Web site. When you do this, your computer sends an electronic request over your Internet connection to your Internet service provider (ISP). The ISP routes the request to a server further up the chain on the Internet. Eventually, the request will hit a domain name server (DNS). This server will look for a match for the domain name you’ve typed in (www.drrajivdesaimd.com). If it finds a match, it will direct your request to the proper server’s IP address. If it doesn’t find a match, it will send the request further up the chain to a server that has more information. The request will eventually come to our Web server. Our server will respond by sending the requested file in a series of packets.

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Peer to Peer file sharing:

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Peer-to-peer file sharing is different from traditional file downloading. In peer-to-peer sharing, you use a software program (rather than your Web browser) to locate computers that have the file you want. Because these are ordinary computers like yours, as opposed to servers, they are called peers. The process works like this:

•You run peer-to-peer file-sharing software (for example, a Gnutella program) on your computer and send out a request for the file you want to download.

•To locate the file, the software queries other computers that are connected to the Internet and running the file-sharing software.

•When the software finds a computer that has the file you want on its hard drive, the download begins.

•Others using the file-sharing software can obtain files they want from your computer’s hard drive.

The file-transfer load is distributed between the computers exchanging files, but file searches and transfers from your computer to others can cause bottlenecks. Some people download files and immediately disconnect without allowing others to obtain files from their system, which is called leeching. This limits the number of computers the software can search for the requested file.  As Peer-to-Peer (P2P) file exchange applications gain popularity, Internet service providers are faced with new challenges and opportunities to sustain and increase profitability from the broadband IP network. Unlike other P2P download methods, BitTorrent maximizes transfer speed by gathering pieces of the file you want and downloading these pieces simultaneously from people who already have them. This process makes popular and very large files, such as videos and television programs, download much faster than is possible with other protocols. Due to the unique and aggressive usage of network resources by Peer-to-Peer technologies, network usage patterns are changing and provisioned capacity is no longer sufficient. Extensive use of Peer-to-Peer file exchange causes network congestion and performance deterioration, and ultimately leads to customer dissatisfaction and churn.

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Note:

Please do not confuse between peering and peer-to-peer file transfer. Peering is direct connection between ISP and content provider (e.g. Google) bypassing internet backbone while peer to peer is sharing files between client computers rather than downloading file from content provider. During peering, you are getting file from content provider at faster speed while during P2P, you are getting file from another user’s computer at faster speed. Peering is violation of net neutrality by ISP while P2P is violation of net neutrality by consumers.

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End-to-end principle:

The principle states that, whenever possible, communications protocol operations should be defined to occur at the end-points of a communications system, or as close as possible to the resource being controlled. This leads to the model of a minimal dumb network with smart terminals, a completely different model from the previous paradigm of the smart network with dumb terminals. All of the intelligence is held by producers and users, not the networks that connect them. End-to-end design of the network entails that the intelligence would be exclusively located at the edges of the Internet (i.e. with end users), and not at the core (i.e. with networks).  If the hosts need a mechanism to provide some functionality, then the network should not interfere or participate in that mechanism unless it absolutely has to. Or, more simply put, the network should mind its own business. If a network function can be implemented correctly and completely using the functionalities available on the end-hosts, that function should be implemented on the end-hosts without delegating any task to the network (i.e., intermediary nodes in between the end-hosts). Because the end-to-end principle is one of the central design principles of the Internet, and because the practical means for implementing data discrimination violate the end-to-end principle, the principle often enters discussions about net neutrality (NN). The end-to-end principle is closely related, and sometimes seen as a direct precursor to the principle of net neutrality.

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The Internet is a global, interconnected and decentralised autonomous computer network. We can access the Internet via connections provided by Internet access providers (ISP). These access providers transmit the information that we send over the Internet in so-called data “packets”. The way in which data is sent and received on the Internet can be compared to sending the pages of a book by post in lots of different envelopes. The post office can send the pages by different routes and, when they are received, the envelopes can be removed and the pages put back together in the right order. When we connect to the Internet, each one of us becomes an endpoint in this global network, with the freedom to connect to any other endpoint, whether this is another person’s computer (“peer-to-peer”), a website, an e-mail system, a video stream or whatever.

The success of the Internet is based on two simple but crucial components of its architecture:

1. Every connected device can connect to every other connected device.

2. All services use the “Internet Protocol,” which is sufficiently flexible and simple to carry all types of content (video, e-mail, messaging etc.) unlike networks that are designed for just one purpose, such as the voice telephony system.

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Technical internet:

Internet is the abbreviation of the term internetwork, which describes the connection between computer networks all around the world on the basis of the same set of communication protocols. At its start in the 1960s, the Internet was a closed research network between just a few universities, intended to transmit text messages. The architectural design of the Internet was guided by two fundamental design principles: Messages are fragmented into data packets that are routed through the network autonomously (end-to-end principle) and as fast as possible (best-effort principle [BE]). This entails that intermediate nodes, so-called routers, do not differentiate packets based on their content or source. Rather, routers maintain routing tables in which they store the next node that lies on the supposedly shortest path to the packet’s destination address. However, as each router acts autonomously along when deciding the path along which it sends a packet, no router has end-to-end control over which path the packet is send from sender to receiver. Moreover, it is possible, even likely, that packets from the same message flow may take different routes through the network. Packets are stored in a router’s queue if they arrive at a faster rate than the rate at which the router can send out packets. If the router’s queue is full, the package is deleted (dropped) and must be resent by the source node. Full router queues are the main reason for congestion on the Internet. However, no matter how important a data packet may be, routers would always process their queue according to the first-in-first-out principle. These fundamental principles always were (and remain in the context of the NN debate) key elements of the open Internet spirit. Essentially, they establish that all data packets sent to the network are treated equally and that no intermediate node can exercise control over the network as a whole. This historic and romantic view of the Internet neglects that Quality of Service (QoS) has always been an issue for the network of networks. Over and beyond the sending of mere text messages, there is a desire for reliable transmission of information that is time critical (low latency), or for which it is desired that data packets are received at a steady rate and in a particular order (low jitter). Voice communication, for example, requires both, low latency and low jitter. This desire for QoS was manifested in the architecture of the Internet as early as January 1, 1983, when the Internet was switched over to the Transmission Control Protocol / Internet Protocol (TCP/IP). In particular, the Internet protocol version 4 (IPv4), which constitutes the nuts and bolts of the Internet since then, already contains a type of service (TOS) field in its header by which routers could prioritize packets in their queues and thereby establish QoS. However, a general agreement on how to handle data with different TOS entries was never reached and thus the TOS field was not used accordingly. Consequently, in telecommunications engineering, research on new protocols and mechanisms to enable QoS in the Internet has spurred ever since, long before the NN debate came to life. In addition, data packets can even be differentiated solely based on what type of data they are carrying, without the need for an explicit marking in the protocol header. This is possible by means of so-called Deep Packet Inspection (DPI). All of these features are currently deployed in the Internet as we know it, and many of them have been deployed for decades. The NN debate, however, sometimes questions the existence and use of QoS mechanisms in the Internet and argues that the success of the Internet was only possible due to the BE principle. While the vision of an Internet that is based purely on the BE principle is certainly not true, some of these claims nevertheless deserve credit.

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Commercial internet:

Another far-reaching event was the steady commercialization of the Internet in the 1990s. At about the same time, the disruptive innovation of content visualization and linkage via the Hyper Text Markup Language (HTML), the so called World Wide Web (WWW) made the Internet a global success. Private firms began to heavily invest in backbone infrastructure and commercial ISPs provided access to the Internet, at first predominately by dial up connections. The average data traffic per household severely increased with the availability of broadband and rich media content (Bauer et al., 2009). According to the Minnesota Internet Traffic Studies (Odlyzko et al., 2012) Internet traffic in the US is growing annually by about 50 percent. The increase in network traffic is the consequence of the on-going transition of the Internet to a fundamental universal access technology. Media consumption using traditional platforms such as broadcasting and cable is declining and content is instead consumed via the Internet. Today the commercial Internet ecosystem consists of several players. Internet users (IUs) are connected to the network by their local access provider (ISP), while content and service providers (CSPs) offer a wide range of applications and content to the mass of potential consumers. All of these actors are spread around the world and interconnect with each other over the Internet’s backbone, which is under the control of an oligopoly of big network providers (Economides, 2005). The Internet has become a trillion dollar industry (Pélissié du Rausas et al., 2011) and has emerged from a mere network of networks to the market of markets. Much of the NN debate is devoted to the question whether the market for Internet access should be a free market, or whether it should be regulated in the sense that some feasible revenue flows are to be prohibited.

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The principal Internet services:

• E‐mail person‐to‐person messaging; document sharing.

• Newsgroups discussion groups on electronic bulletin boards.

• Chatting and instant messaging interactive conversations.

• Telnet logging on to one computer system and doing work on another.

• File Transfer Protocol (FTP) transferring files from computer to computer.

• World Wide Web retrieving, formatting, and displaying information (including text, audio, graphics, and video) using hypertext links.

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The modern Internet was invented to be a free and open network that allows anyone with a Web connection to communicate directly with any individual or computer on that network. Over the past 25 years, the Internet has transformed the way we do just about everything. Think about the conveniences and services that wouldn’t exist without the Internet:

• instant access to information about everything email

• online shopping

• online social networks

• independent global news sources

• streaming movies, TV shows and music

• online banking

• video calls and videoconferencing

The Internet has evolved so quickly and works so well precisely because the technology behind the Internet is neutral. In other words, the physical cables, routers, switches, servers and software that run the Internet treat every byte of data equally. A streaming movie from Netflix shares the same crowded fiber optic cable as the pictures from your niece’s birthday. The Internet doesn’t pick favourites. That, at its core, is what net neutrality means. And that’s one of the most important reasons why you should care about it: to keep the Internet as free, open and fair as possible, just as it was designed to be.

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Networking:

Networking allows one computer to send information to and receive information from another. We may not always be aware of the numerous times we access information on computer networks. Certainly the Internet is the most conspicuous example of computer networking, linking millions of computers around the world, but smaller networks play a role in information access on a daily basis. We can classify network technologies as belonging to one of two basic groups. Local area network (LAN) technologies connect many devices that are relatively close to each other. Wide area network (WAN) technologies connect a smaller number of devices that can be many kilometers apart. Ethernet is a wired LAN technology while Wi-Fi is wireless LAN technology. WAN is a computer networking technologies used to transmit data over long distances, and between different LANs and other localised computer networking architectures. Network nodes can be connected using any given technology, from circuit switched telephone lines (DSL) through radio waves (wireless broadband/mobile broadband) through optic fibre.

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Broadband network:

The ideal telecommunication network has the following characteristics: broadband, multi-media, multi-point, multi-rate and economical implementation for a diversity of services (multi-services). The Broadband Integrated Services Digital Network (B-ISDN) intended to provide these characteristics. Asynchronous Transfer Mode (ATM) was promoted as a target technology for meeting these requirements.

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Multi-media:

A multi-media call may communicate audio, data, still images, or full-motion video, or any combination of these media. Each medium has different demands for communication quality, such as:

1. bandwidth requirement,

2. signal latency within the network, and

3. signal fidelity upon delivery by the network.

The information content of each medium may affect the information generated by other media. For example, voice could be transcribed into data via voice recognition, and data commands may control the way voice and video are presented. These interactions most often occur at the communication terminals, but may also occur within the network.

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Internet access:

Internet access connects individual computer terminals, computers, mobile devices, and computer networks to the Internet, enabling users to access Internet services, such as email and the World Wide Web. Internet service providers (ISPs) offer Internet access through various technologies that offer a wide range of data signalling rates (speeds). Consumer use of the Internet first became popular through dial-up Internet access in the 1990s. By the first decade of the 21st century, many consumers in developed nations used faster, broadband Internet access technologies. As of 2014, broadband was ubiquitous around the world, with a global average connection speed exceeding 4 Mbit/s.

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Choosing an Internet service:

It all depends on where you live and how much speed you need. Internet service providers (ISPs) usually offer different levels of speed based on your needs. If you’re mainly using the Internet for email and social networking, a slower connection might be all you need. However, if you want to download a lot of music or watch streaming movies, you’ll want a faster connection. You’ll need to do some research to find out what the options are in your area. Here are some common types of Internet service.

Dial-up:

Dial-up is generally the slowest type of Internet connection, and you should probably avoid it unless it is the only service available in your area. Like a phone call, a dial-up modem will connect you to the Internet by dialling a number, and it will disconnect when you are done surfing the Web. Unless you have multiple phone lines, you will not be able to use your land line and the Internet at the same time with a dial-up connection.

DSL (digital subscriber line):

DSL service uses a broadband connection, which makes it much faster than dial-up. DSL is a high-speed Internet service like cable Internet. DSL provides high-speed networking over ordinary phone lines using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections. DSL technology theoretically supports data rates of 8.448 Mbps, although typical rates are 1.544 Mbps or lower. DSL Internet services are used primarily in homes and small businesses. DSL Internet service only works over a limited physical distance and remains unavailable in many areas where the local telephone infrastructure does not support DSL technology. However, it is unavailable in many locations, so you’ll need to contact your local ISP for information about your area. DSL connects to the Internet via phone line but does not require you to have a land line at home. Unlike dial-up, it will always be on once its set up, and you’ll be able to use the Internet and your phone line simultaneously.

Cable:

Cable service connects to the Internet via cable TV, although you do not necessarily need to have cable TV in order to get it. It uses a broadband connection and can be faster than both dial-up and DSL service; however, it is only available in places where cable TV is available.

Satellite:

A satellite connection uses broadband but does not require cable or phone lines; it connects to the Internet through satellites orbiting the Earth. As a result, it can be used almost anywhere in the world, but the connection may be affected by weather patterns. A satellite connection also relays data on a delay, so it is not the best option for people who use real-time applications, like gaming or video conferencing.

3G and 4G:

3G and 4G service is most commonly used with mobile phones and tablet computers, and it connects wirelessly through your ISP’s network. If you have a device that’s 3G or 4G enabled, you’ll be able to use it to access the Internet away from home, even when there is no Wi-Fi connection. However, you may have to pay per device to use a 3G or 4G connection, and it may not be as fast as DSL or cable.

Wireless hotspots:

If you’re out and about with an internet device like a laptop, tablet or smartphone, you might want to connect at a wireless hotspot. Wireless ‘hotspots’ are places like libraries and cafés, which offer you free access to their broadband connection (Wi-Fi). You may need to be a member of the library or a customer at a café to get the password for the wireless connection.

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Wired vs. wireless internet access:

A wired network connects devices to the Internet or other network using cables. The most common wired networks use cables connected to Ethernet ports on the network router on one end and to a computer or other device on the cable’s opposite end. A wireless local-area network (LAN) uses radio waves to connect devices such as laptops to the Internet and to your business network and its applications. When you connect a laptop to a Wi-Fi hotspot at a cafe, hotel, airport lounge, or other public place, you’re connecting to that business’s wireless network. Almost all of the discussion surrounding net neutrality has been confined to wired (that is, cable, DSL and fiber) broadband in the U.S. while in India, most internet is wireless mobile broadband. In India they have an abnormally high mobile to fixed broadband ratio of 4:1 and only 15.2 million wired broadband connections in a country of 1.25 billion. India has a fixed broadband penetration ratio of 1.2 per 100 as against the world average of 9.4 per 100. The Open Internet Order by FCC adopted definitions for “fixed” and “mobile” Internet access service. It defined “fixed broadband Internet access service” to expressly include “broadband Internet access service that serves end users primarily at fixed endpoints using stationary equipment … fixed wireless services (including fixed unlicensed wireless services), and fixed satellite services.”  It defined “mobile broadband Internet access service” as “a broadband Internet access service that serves end users primarily using mobile stations.” So fixed internet access include wired and wireless technology while mobile internet access is always wireless. The transparency rule applies equally to both fixed and mobile broadband Internet access service. The no-blocking rule applied a different standard to mobile broadband Internet access services and mobile Internet access service was excluded from the unreasonable discrimination rule.

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Wired network Wireless network
Consumers use cable (cable TV), copper wire (DSL) or fiber-optic to connect to internet Consumers use radio waves to connect to internet via 3G/4G data card containing modem (mobile broadband) or through Wi-Fi using LAN
Large capacity of data transmission, volume uncapped It requires the use of spectrum, which is a scarce public resource,  limited capacity of data transmission,  restrictive volume caps
Multiple simultaneous users do not significantly affect speed Multiple simultaneous users significantly reduces speed
Majority of American population uses wired network Majority of Indian population uses wireless network
Net neutrality debate mainly involve wired transmission in America Net neutrality debate mainly involve wireless transmission in India
Wired connection speed is near maximum throughput Wireless connection speed will be less than the maximum throughput due to various factors reducing signal strength
Wired connection generally have faster internet speed Wireless connection generally have slower internet speed
You have to access internet at a fixed point You can move around with device within network coverage area for internet access
Voice and video quality not significantly affected in network congestion Voice and video quality significantly affected in network congestion

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What is spectrum?

Spectrum in wireless telephone/internet transmission is the radio frequency spectrum that ranges from very low frequency radio waves at around 10kHz (30 kilometres wavelength) up to 100GHz (3 millimetres wavelength). The radio spectrum is divided into frequency bands reserved for a single use or a range of compatible uses. Within each band, individual transmitters often use separate frequencies, or channels, so they do not interfere with each other. Because there are so many competing uses for wireless communication, strict rules are necessary to prevent one type of transmission from interfering with the next. And because spectrum is limited — there are only so many frequency bands — governments must oversee appropriate licensing of this valuable resource to facilitate use in all bands. Governments spend a considerable amount of time allocating particular frequencies for particular services, so that one service does not interfere with another. These allocations are agreed internationally, so that interference across borders, as well as between services, is minimised. Not all radio frequencies are equal. In general, lower frequencies can reach further beyond the visible horizon and are better at penetrating physical obstacles such as rain or buildings. Higher frequencies have greater data-carrying capacity, but less range and ability to pass through obstacles. For example, Mobile broadband uses the spectrum of 225 MHz to 3700 MHz while Wi-Fi uses 2.4 and 5 GHz frequency. Capacity is also dependent on the amount of spectrum a service uses — the channel bandwidth. For many wireless applications, the best trade-off of these factors occurs in the frequency range of roughly 400MHz to 4GHz, and there is great demand for this portion of the radio spectrum.

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All communication devices that use digital radio transmissions operate in a similar way. A transmitter generates a signal that contains encoded voice, video or data at a specific radio frequency, and this is radiated into the environment by an antenna (also known as an aerial). This signal spreads out in the environment, of which a very small portion is captured by the antenna of the receiving device, which then decodes the information. The received signal is incredibly weak — often only one part in a trillion of what was transmitted. In the case of a mobile phone call, a caller’s voice is converted by the handset into digital data, transmitted via radio to the network operator’s nearest tower or base station, transferred to another base station serving the recipient’s location, and then transmitted again to the recipient’s phone, which converts the signal back into audio through the earpiece. There are a number of standards for mobile phones and base stations, such as GSM, WCDMA and LTE, which use different methods for coding and decoding, and ensure that users can only receive voice calls and data that are intended for them.

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The bandwidth of a radio signal is the difference between the upper and lower frequencies of the signal. For example, in the case of a voice signal having a minimum frequency of 200 hertz (Hz) and a maximum frequency of 3,000 Hz, the bandwidth is 2,800 Hz (3 KHz). The amount of bandwidth needed for 3G services could be as much as 15-20 Mhz, whereas for 2G services a bandwidth of 30-200 KHz is used. Hence, for 3G huge bandwidth is required. Please do not confuse between bandwidth of 2G/3G spectrum and bandwidth of internet transmission i.e. internet speed.

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What is Broadband?

Broadband is a technology that transmits data at high speed along cables, ISDN / DSLs (Digital Subscriber Lines) and mobile phone networks. The most common type of broadband is ADSL (carried along phone lines), though cable (using new fibre-optic cables) and mobile broadband (using 3G and 4G mobile reception) are hot contenders to topple ADSL’s dominance. ADSL broadband comes from your local telephone exchange, through a Fixed Line Access Network made out of copper wires. These are the telephone lines that you see in the street. The lines in the street connect to the wiring inside your house and provide you an internet and phone connection through the socket on the wall. Unlike the copper wires of an ADSL connection, cables are partially made of fibre-optic material, which allows for much faster broadband speeds and increased reliability. The other advantage of cable is that it also allows for the transmission of audio and visual signals, which means you can get both landline and digital TV services from your cable broadband provider. Mobile broadband uses 3G and 4G mobile phone technology. These are made possible by two complementary technologies, HSDPA and HSUPA (high speed download and upload packet access, respectively).

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Broadband provides improved access to Internet services such as:

1. Faster World Wide Web browsing

2. Faster downloading of documents, photographs, videos, and other large file

3. Telephony, radio, television, and videoconferencing

4. Virtual private networks and remote system administration

5. Online gaming, especially massively multiplayer online role-playing games which are interaction-intensive

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Broadband technologies supply considerably higher bit rates than dial-up, generally without disrupting regular telephone use. Various minimum data rates and maximum latencies have been used in definitions of broadband, ranging from 64 kbit/s up to 4.0 Mbit/s. In 1988 the CCITT standards body defined “broadband service” as requiring transmission channels capable of supporting bit rates greater than the primary rate which ranged from about 1.5 to 2 Mbit/s.  A 2006 Organization for Economic Co-operation and Development (OECD) report defined broadband as having download data transfer rates equal to or faster than 256 kbit/s.  And in 2015 the U.S. Federal Communications Commission (FCC) defined “Basic Broadband” as data transmission speeds of at least 25 Mbit/s downstream (from the Internet to the user’s computer) and 3 Mbit/s upstream (from the user’s computer to the Internet). The trend is to raise the threshold of the broadband definition as higher data rate services become available.

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Broadband infrastructure:

Proponents of net neutrality regulations say network operators have continued to under-invest in infrastructure. However, according to Copenhagen Economics, US investment in telecom infrastructure is 50 percent higher that of the European Union. As a share of GDP, The US’s broadband investment rate per GDP trails only the UK and South Korea slightly, but exceeds Japan, Canada, Italy, Germany, and France sizably.  On broadband speed, Akamai reported that the US trails only South Korea and Japan among its major trading partners, and trails only Japan in the G-7 in both average peak connection speed and percentage of the population connection at 10 Mbit/s or higher, but are substantially ahead of most of its other major trading partners. The White House reported in June 2013 that U.S. connection speeds are the fastest compared to other countries with either a similar population or land mass. Broadband speeds in the United States, both wired and wireless, are significantly faster than those in Europe. Broadband investment in the United States is several multiples that of Europe. And broadband’s reach is much wider in the United States, despite its much lower population density. In other words, broadband speed is directly proportional to investment in broadband infrastructure. I live in small town Daman where maximum internet download speed I got from any ISP is 2.5 Mbps. This is because of poor broadband infrastructure in India.

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Bandwidth (internet speed):

In computer networks, bandwidth is used as a synonym for data transfer rate (internet speed), the amount of data that can be carried from one point to another in a given time period (usually a second). Network bandwidth is usually expressed in bits per second (bps); modern networks typically have speeds measured in the millions of bits per second (megabits per second, or Mbps) or billions of bits per second (gigabits per second, or Gbps). How fast your internet is depends on three factors: Download speed (how fast you can retrieve something from the internet), upload speed (sending something to a remote location on the internet), and latency (lag time between each point during information transfer). Download speed is what you experience the most and can send you to tap your fingers for what seems like minutes before a web page shows up on your screen. If you’re streaming movies from Netflix, download speed is important. The higher the number for download speed, the quicker the movie will get from the Netflix website to your computer. A movie downloaded at 15 Mbps should take one-tenth as long as having a 1.5 Mbps connection. Note that bandwidth is not the only factor that affects network performance: There is also packet loss, latency and jitter, all of which degrade network throughput and make a link perform like one with lower bandwidth.  A network path usually consists of a succession of links, each with its own bandwidth, so the end-to-end bandwidth is limited to the bandwidth of the lowest speed link (the bottleneck). Different applications require different bandwidths. This is important because some sites use much more bandwidth than others depending on their content and media. Video is one of the main ways to use a lot of bandwidth.  For example, sites like Netflix and YouTube use almost half of North America’s Internet Bandwidth during peak hours of the day (according to CNET). An instant messaging conversation might take less than 1,000 bits per second (bps); a voice over IP (VoIP) conversation requires 56 kilobits per second (Kbps) to sound smooth and clear.  Standard definition video (480p) works at 1 megabit per second (Mbps), but HD video (720p) wants around 4 Mbps, and HDX (1080p), more than 7 Mbps. Effective bandwidth — the highest reliable transmission rate a path can provide — is measured with a bandwidth test. This rate can be determined by repeatedly measuring the time required for a specific file to leave its point of origin and successfully download at its destination.

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Speed vs. latency:

There is more to an Internet connection’s speed than just its bandwidth. This is especially true with satellite Internet connections, which can offer speeds of up to 15 Mbps – but will still feel slow. Latency is defined as the time it takes for a source to send a packet of data to a receiver. Latency is typically measured in milliseconds. Latency is independent of internet speed. Consider the analogy of a car travelling at 100 mph from A to B. This might sound fast but gives no indication of whether the car has driven the most direct route; if direct, fine; if from A to C to D to B the journey is going to take longer. So with network traffic; you might have a fast Internet connection, but if the route between the user’s computer and the server being accessed is indirect, response times will be slower. Latency is a true indicator of whether network traffic has taken the shortest possible route. The lower the latency (the fewer the milliseconds), the better the network performance. Together, latency and bandwidth define the speed and capacity of a network. Network latency is the term used to indicate any kind of delay that happens in data communication over a network. Network connections in which small delays occur are called low-latency networks whereas network connections which suffer from long delays are called high-latency networks. High latency creates bottlenecks in any network communication. It prevents the data from taking full advantage of the network pipe and effectively decreases the communication bandwidth. The impact of latency on network bandwidth can be temporary or persistent based on the source of the delays. On DSL or cable Internet connections, latencies of less than 100 milliseconds (ms) are typical and less than 25 ms desired. Satellite Internet connections, on the other hand, average 500 ms or higher latency. Wireless mobile broadband latency varies from 80 ms (LTE) to 125 ms (HSPA).

How to measure latency:

Ping Command:

One of the first things to try when your connection doesn’t seem to be working properly is the ping command. Open a Command Prompt window from your Start menu and run a command like ping google.com or ping howtogeek.com. This command sends several packets to the address you specify. The web server responds to each packet it receives. In the command below, you can see % of packet loss and the time each packet takes. Ping cannot perform accurate measurements, principally because it uses the ICMP protocol that is used only for diagnostic or control purposes, and differs from real communication protocols such as TCP. Furthermore routers and ISP’s might apply different traffic shaping policies to different protocols. For more accurate measurements it is better to use specific software (for example: lft, paketto, hping, superping.d, NetPerf, IPerf)

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A very good example when bandwidth would directly correlate to speed is when you are downloading a file across the network or Internet. Greater bandwidth means that more of the file is being transferred at any given time. The file would be therefore be downloaded faster. This is also applicable when you are browsing the Internet as greater bandwidth would result in web pages loading faster and video streaming to be smoother. But in certain cases, speed and bandwidth do not literally mean the same thing. This is true when you talk about real time applications like VoIP or online gaming. In these cases, latency or response time is more important than having more bandwidth. Even if you have a lot of bandwidth, you may experience choppy voice transmission or response lag if your latency is too high. Upgrading your bandwidth would probably not help since it would no longer be used. Latency can’t be upgraded easily as it requires that any noise be minimized as well as the amount of time that it takes for packets to move from source to destination and vice versa. To obtain the best possible speed for your network or Internet connection, it is not enough to have a high bandwidth connection. It is also important that your latency is low, to ensure that the information reaches you quickly enough. This only matters though if you have enough bandwidth as low latencies without enough bandwidth would still result in a very slow connection.

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The speed at which websites download from the Internet is dependent on the following factors:

1. Web design:

•Design of the web page – number of graphics and their size, use of frames and tables

•Size of the web page – overall length of page. Note; having valid, compliant html/css coding on your website will allow your browser to render the page much more quickly

2. Your browsing history:

•Whether or not you have ever accessed the site before. If you have accessed it recently, the files may be in your cache and the site will load more quickly the second and subsequent times.

•How full your web browser cache is – you may need to clear your cache if you’ve set it to only reserve a small amount of space.

3. Your computer configuration and settings:

•How much memory you have in your computer – the more RAM the better.

•The size of your network buffer – most overlooked setting, have your IT staff review the settings.

•How fragmented the data on your hard drive is – you may need to run a defragment program.

•The number of programs you have running simultaneously while downloading. Running multiple programs hogs valuable RAM space.

•Cookies should be cleared regularly (bi-weekly or monthly) to help reduce the load on your browser thus slowing down your performance.

4. The network used to access the site:

•Speed of your connection to the Internet – your modem/cable/DSL/wireless speed.

•Quality of your telephone/broadband line – bad connections mean slower transmissions.

•Access speed on the server where the site is hosted – if the site is hosted on a busy server, it may slow down access speed.

•How much traffic there is to the site at the same time you are trying to access it.

•The load on the overall network at your ISP – how busy it is.

Any or all of the above can slow download time. Web designers only have control over the first two items!

5. Limitations of your computer:

There are also other ways you can improve your speeds, here are a few:

• Update to the latest Web browser and Operation System versions.

•Clear out your cache: Old information retained by your web browser may be making it perform slower than it could.

•Reformatting your hard drive: Although technical in nature, by reloading your Operating System, you will be able to get rid of unnecessary files that linger around your computer.

•Change your ISP: As drastic as this may sound, some providers oversell their services. As a result, they simply cannot supply their users with speeds needed by modern day web activities. Before you take the plunge to get a new ISP, make sure you read some reviews about them and ask your friends for recommendation.

•It may be time for an upgrade! Get a new computer! Modern software programs take up more and more resources and it is quite possible that your current hardware simply cannot keep up to date with the current standards.

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There are other factors involved in internet speed:

1. End-User Hardware Issues: If you have an old router that just can’t keep up with modern speeds or a poorly configured Wi-Fi connection that’s being slowed down by interference, you won’t actually experience the connection speeds you’re paying for — and that’s not the Internet service provider’s fault.

2. Distance from ISP: The further you are away from your Internet service provider’s hardware, the weaker your signal can become. If you’re in a city, you’re likely to have a faster connection than you would in the middle of the countryside.

3. Congestion: You’re sharing an Internet connection line with many other customers from your Internet service provider, so congestion can result as all these people compete for the Internet connection. This is particularly true if all your neighbours are using BitTorrent 24/7 or using other demanding applications.

4. Time of Day: Because more people are probably using the shared connection line during peak hours — around 6pm to midnight for residential connections — you may experience slower speeds at these times.

5. Throttling; Your Internet service provider may slow down (or “throttle”) certain types of traffic, such as peer-to-peer traffic. Even if they advertise “unlimited” usage, they may slow down your connection for the rest of the month after you hit a certain amount of data downloaded. Throttling is a process by which the amount of bandwidth you use through your Internet provider is limited in some way, usually in the form of slower upload or download speeds. This is done to allow others to more effectively connect to the Internet Service Provider’s servers. Net neutrality supporters are concerned with throttling because they believe current legislation is leaving the doors open to allow ISPs to throttle based on their own discretion of what sites you visit. For example, if you plan to watch “House of Cards” in UltraHD on Netflix, but your ISP decides it’s going to “throttle” access to Netflix, you may have to settle for some grainy 720p or worse, 480p on your new giant, curved Ultra HDTV.

6. Server-Side Issues: Your download speeds don’t just depend on your Internet service provider’s advertised speeds. They also depend on the speeds of the servers you’re downloading from and the routers in between. For example, if you’re in the US and experience slowness when downloading something from a website in Europe, it may not be your Internet service provider’s fault at all — it may be because the website in Europe has a slow connection or the data is being slowed down at one of the routers in between you and the European servers.

Many factors can impact Internet connection speed, and it’s hard to know which is the precise problem. Nevertheless, in real-life usage, you’ll generally experience slower speeds than your Internet service provider advertises — if only because it’s so dependent on other people’s Internet connections.

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Can your download/upload speed affected by number of simultaneous users on any network, wired or wireless?

Simply yes!

The more users on any network, wired or wireless, the less bandwidth available to each of them. The type of activity also has a huge impact on performance.  If everyone is only checking e-mail it’s not likely to cause slowdowns. But if you have someone trying to stream a Netflix movie and someone else running a Skype video chat you can probably forget about playing an online game as well.

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When multiple connected computers or devices – such as a mobile phone and wireless router – connect simultaneously to the same network, the result of having to share the available bandwidth, Internet access speed could be reduced. Wireless connection throughput is subject to conditions such as the local radio environment, number of devices sharing the same wireless network, range of the wireless coverage, interferences, physical obstacles and capability of receiving end. As a result, actual wireless connection speed will be less than the maximum throughput. In practice very few wireless networks can ever achieve their full quoted data rate. It is strongly dependant on signal strength. There are then various overheads, for TCP, IP and the wireless transport layer, including traffic that manages the connection even if you are not actively using it currently. These overheads include acknowledgments that need to be sent when data is received (and vice-versa).  Each website is served by a server connected to the network, and network bandwidth is distributed according to a website’s usage. So when the number of users is low, your connection speed will be faster. In contrast, when the number of simultaneous users is high, your linking network server will be congested, causing the connection speed to drop, especially for an overseas network server and the amount of users.  In summary, the end-to-end data throughput is also dependent on the bandwidth of the connection from the web or network server to the internet. The speed of the flow not only depends on bandwidth and number of users but also depends on routers and network conditions between the two devices involved in the flow.

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Upstream and Downstream Bandwidth:

When a device uses the Internet, information flows in two ways: to the device and from the device. When data flows to the device, the movement of information is downstream. When data flows from the device, the movement is upstream. Typical Internet processes involve more downstream usage than upstream usage; information flows to the device more than it flows from it. As a result, most Internet connections prioritize downstream bandwidth. However, for large data transfers, remote access, video chats and voice over IP calls, more upstream bandwidth is required. Many Internet routers have Quality of Service, or QoS, settings that can prioritize bandwidth usage in the case of increased upstream flow.

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Multiple Users of a Single Connection:

When multiple people use a single connection, more devices consume the finite bandwidth of the connection. Therefore, each device is allocated a smaller portion of the available bandwidth. As a result, all devices may experience a slower data transfer. Some router QoS settings allow you to prioritize device bandwidth use so that certain devices have increased access to the bandwidth.

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Now let me discuss two human factors responsible for provoking humans to choose one site over another besides obvious cost & quality factors:

1. Human intolerance for slow-loading sites

2. Human audio-visual perception

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Consumer intolerance to slow-loading sites:

Video Stream Quality impacts viewer behaviour:

The Internet is radically transforming all aspects of human society by enabling a wide range of applications for business, commerce, entertainment, news and social networking. Perhaps no industry has been transformed more radically than the media and entertainment segment of the economy. As media such as television and movies migrate to the Internet, there are twin challenges that content providers face whose ranks include major media companies (e.g., NBC, CBS), news outlets (e.g., CNN), sports organizations (e.g., NFL, MLB), and video subscription services (e.g., Netflix, Hulu). The first major challenge for content providers is providing a high-quality streaming experience for their viewers, where videos are available without failure, they startup quickly, and stream without interruptions. A major technological innovation of the past decade that allows content providers to deliver higher-quality video streams to a global audience of viewers is the content delivery network (or, CDN for short). CDNs are large distributed systems that consist of hundreds of thousands of servers placed in thousands of ISPs close to end users. CDNs employ several techniques for transporting media content from the content provider’s origin to servers at the “edges” of the Internet where they are cached and served with higher quality to the end user. The second major challenge of a content provider is to actually monetize their video content through ad-based or subscription-based models. Content providers track key metrics of viewer behavior that lead to better monetization. Primary among them relate to viewer abandonment, engagement, and repeat viewership. Content providers know that reducing the abandonment rate, increasing the play time of each video watched, and enhancing the rate at which viewers return to their site increase opportunities for advertising and upselling, leading to greater revenues. The key question is whether and by how much increased stream quality can cause changes in viewer behavior that are conducive to improved monetization. Relatively little is known from a scientific standpoint about the all-important causal link between video stream quality and viewer behavior for online media. While understanding the link between stream quality and viewer behavior is of paramount importance to the content provider, it also has profound implications for how a CDN must be architected. An architect is often faced with trade-offs on which quality metrics need to be optimized by the CDN. A scientific study of which quality metrics have the most impact on viewer behavior can guide these choices. As an example of viewer behavior impacting CDN architecture, authors performed small-scale controlled experiments on viewer behavior a decade ago that established the relative importance of the video to startup quickly and play without interruptions. These behavioral studies motivated an architectural feature called prebursting that was deployed on Akamai’s live streaming network that enabled the CDN to deliver streams to a media player at higher than the encoded rate for short periods of time to fill the media player’s buffer with more data more quickly, resulting in the stream starting up faster and playing with fewer interruptions. It is notable that the folklore on the importance of startup time and rebuffering were confirmed in two recent important large-scale scientific studies. The current work sheds further light on the important nexus between stream quality and viewer behavior and, importantly, provides the first evidence of a causal impact of quality on behavior.

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Authors study the impact of video stream quality on viewer behavior in a scientific data-driven manner by using extensive traces from Akamai’s streaming network that include 23 million views from 6.7 million unique viewers. They show that viewers start to abandon a video if it takes more than 2 seconds to start up, with each incremental delay of 1 second resulting in a 5.8% increase in the abandonment rate. Further, they show that a moderate amount of interruptions can decrease the average play time of a viewer by a significant amount. A viewer who experiences a rebuffer delay equal to 1% of the video duration plays 5% less of the video in comparison to a similar viewer who experienced no rebuffering. Finally, authors show that a viewer who experienced failure is 2.32% less likely to revisit the same site within a week than a similar viewer who did not experience a failure.  On average, YouTube streams 4 billion hours of video per month. That’s a lot of video, but it’s only a fraction of the larger online-streaming ecosystem. For video-streaming services, making sure clips always load properly is extremely challenging, and this study reveals that it’s important to video providers, too. Maybe this has happened to you: You’re showing a friend some hilarious video that you found online. And right before you get to the punch line, a little loading dial pops up in the middle of the screen. Buffering kills comedic timing, and according to this study it kills attention spans, too.  People are pretty patient for up to two seconds. If you start out with, say, 100 users — if the video hasn’t started in five seconds, about one-quarter of those viewers are gone, and if the video doesn’t start in 10 seconds, almost half of those viewers are gone. If a video doesn’t load in time, people get frustrated and click away. This may not come as a shock, but until now it hadn’t come as an empirically supported fact, either. This is really the first large-scale study of its kind that tries to relate video-streaming quality to viewer behavior.

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User intolerance for slow-loading sites:

The figure above shows abandonment rate of online video users for different Internet connectivities.  Users with faster Internet connectivity (e.g., fiber) abandon a slow-loading video at a faster rate than users with slower Internet connectivity (e.g., cable or mobile).  A “fast lane” in the Internet can irrevocably decrease the user’s tolerance to the relative slowness of the “slow lane”.

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Voice, video and human perception:

Voice and video signals must come fast and in a specific sequence. Conversations become difficult if words or syllables go missing or are delayed by more than a couple of tenths of a second. Our eyes can tolerate a bit more variation in video than our ears can tolerate in voice; on the other hand, video needs much more bandwidth. The human hearing system does not tolerate these flaws well because of its acute sense of timing. Twenty milliseconds of sudden silence can disturb a conversation. Voice and video can be converted into series of packets coded to identify their contents as requiring transmission at a regular rate. For telephony, the packet priority codes are designed to keep the conversation flowing without annoying jitter—variations in when the packets are received. Similar codes help keep video packets flowing at the proper rate. In practice, these flow controls are not crucial in today’s fixed broadband networks, which generally have enough capacity to transmit voice and video. But mobile apps are a different story. The Internet discards packets that arrive after a maximum delay, and it can request retransmission of missing packets. That’s okay for Web pages and downloads, but real-time conversations can’t wait. Software may skip a missing packet or fill the gap by repeating the previous packet. That’s tolerable for vowels, which are long, even sounds, so a packet lost from the middle of “zoom” would go unnoticed. But consonants are short and sharp, so losing a packet at the end of “can’t” turns it into “can.” Severe congestion can cause whole sentences to vanish and make conversation impossible. Such congestion is most serious on wireless networks, and it also already affects fixed broadband and backbone networks. Consumers frustrated by long video-buffering delays sometimes blame cable companies for intentionally throttling streaming video from companies like Netflix. But in 2014 the Measurement Lab consortium reported that the real bottlenecks are at interconnections between Internet access providers and backbone networks.

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Is internet common carrier?

In common law countries, common carrier is a legal classification for a person or company which transports goods and is legally prohibited from discriminating or refusing service based on the customer or nature of the goods. The common carrier framework is often used to classify public utilities, such as electricity or water, and public transport. In the United States, there has been intense debate between some advocates of net neutrality, who believe Internet providers should be legally designated common carriers, and some Internet service providers, who believe the common carrier designation would be a heavy regulatory burden. You expect your home Internet connection to “just work” like water and electricity. But what if the electric company provided inadequate power to your Whirlpool refrigerator, because Whirlpool hadn’t paid a fee? And what if the water company completely cut off the flow from your Kohler faucet because it owned a stake in another faucet company? Unlike public utilities, your Internet service provider (ISP) can abuse its power to influence which Internet businesses win and lose by slowing down or even blocking sites and services.  The idea that the Internet should be operated like a public “road” — carrying all traffic, with no discrimination against any traveller, no matter what size, shape or type — seems to many a bedrock principle. But should the Internet be regulated like other public utilities — like water or electricity? Under FCC policy, Internet service providers such as Verizon and Comcast (ISPs)had to treat all content equally, including news sites, Facebook and Twitter, cloud-based business activities, role-playing games, Netflix videos, peer-to-peer music file sharing, photos on Flickr — even gambling activity and pornography. Citizens can run all manner of applications and devices, and no content provider is given preferential treatment or a faster “lane” than anyone else. No content can be blocked by Internet service providers or charged differential rates. But it also meant that ISPs could not sell faster services to businesses willing to pay, a form of market regulation that, critics say, stifles innovation and legitimate commercial activity.

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Is Internet an Information Service or a Telecommunications Service?

Another major issue in the Net Neutrality kerfuffle is whether the Internet is classified as an information service or a more regulated telecommunications service. The fact that the Internet was reclassified as an information service by the FCC in 2002, led to Verizon’s successful challenge of Net Neutrality rules. Net Neutrality proponents obviously want the Internet reclassified as a telecommunications service. They feel this extra regulation will allow the principles of Net Neutrality to once again guide the concept of a free Internet. Considering that many of you only have one or two options when choosing a local ISP, regulation may be ultimately necessary to prevent monopoly abuse. If telecommunications companies are successful in instituting an Internet fast lane for video traffic, expect your Netflix subscription to increase by $5 – 10 per month, especially with Ultra HD becoming more popular. The spectre of ISPs blocking content from other competing entities is another issue that may have to be solved separately from the Internet “fast lane” issue.

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ISP (internet service/access provider):

Should ISPs be allowed to selectively prioritize communications between their customers and specific destinations on internet or should the transmission of data be done in a neutral way that does not consider the destination of a communication?  Can ISPs arbitrarily assign preference to business partners or their own content?  Can they charge additional fees to content providers for “priority” connections?  Could they even arbitrarily block or severely degrade communications by their users to competitors such as competing Internet telephone (VoIP) companies, search engines, and online stores?  For all the promise of the Internet, there is a serious threat to its potential for revitalizing democracy. The danger arises because there is, in most markets, a very small number of broadband network operators, and this may not change in the near future.

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To understand what the ISPs are implying here, consider figure above. From an economic point of view ISPs are the operators of a two-sided market platform that connects the suppliers of content and services (CSPs) with the consumers (IUs) that demand these services. In a two-sided market, each side prefers to have many partners on the