147 Sentences With "oxygen toxicity" | Random Sentence Generator

It may prevent oxygen toxicity among deep-water Navy SEAL divers, ease the fuel burden of ultra-endurance athletes, or augment cancer therapies.

The supplementation of oxygen can lead to oxygen toxicity, also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning. There are two main types of oxygen toxicity: central nervous system toxicity (CNS), and pulmonary and ocular toxicity. Temporary exposure to high partial pressures of oxygen at greater than atmospheric pressure can lead to central nervous system toxicity (CNS). An early but serious sign of CNS oxygen toxicity is a grand-mal seizure, also known as a generalized tonic-clonic seizure.

Oxygen toxicity has now become a rare occurrence other than when caused by equipment malfunction and human error. Historically, the U.S. Navy has refined its Navy Diving Manual Tables to reduce oxygen toxicity incidents. Between 1995 and 1999, reports showed 405 surface-supported dives using the helium–oxygen tables; of these, oxygen toxicity symptoms were observed on 6 dives (1.5%). As a result, the U.S. Navy in 2000 modified the schedules and conducted field tests of 150 dives, none of which produced symptoms of oxygen toxicity. Revised tables were published in 2001.

Studies show that, in the long term, a robust recovery from most types of oxygen toxicity is possible. Protocols for avoidance of the effects of hyperoxia exist in fields where oxygen is breathed at higher-than- normal partial pressures, including underwater diving using compressed breathing gases. These protocols have resulted in the increasing rarity of seizures due to oxygen toxicity. Central nervous system oxygen toxicity manifests as symptoms such as visual changes (especially tunnel vision), ringing in the ears (tinnitus), nausea, twitching (especially of the face), behavioural changes (irritability, anxiety, confusion), and dizziness.

Prolonged exposure to higher oxygen levels at atmospheric pressure can lead to pulmonary and ocular toxicity. Symptoms of oxygen toxicity may include disorientation, respiratory problems, or myopia. Prolonged exposure to higher than normal partial pressures of oxygen can result in oxidative damage to cell membranes. Signs of pulmonary (lung) oxygen toxicity begin with slight irritation in the trachea.

Breathing high-pressure gas constitutes a hazard with associated risks of decompression sickness, nitrogen narcosis, oxygen toxicity and high-pressure nervous syndrome.

Both oxygen toxicity and relative hypoxia can contribute to the development of ROP. It was first reported by Theodore L. Terry in 1942.

Diagnosis of central nervous system oxygen toxicity in divers prior to seizure is difficult as the symptoms of visual disturbance, ear problems, dizziness, confusion and nausea can be due to many factors common to the underwater environment such as narcosis, congestion and coldness. However, these symptoms may be helpful in diagnosing the first stages of oxygen toxicity in patients undergoing hyperbaric oxygen therapy. In either case, unless there is a prior history of epilepsy or tests indicate hypoglycaemia, a seizure occurring in the setting of breathing oxygen at partial pressures greater than suggests a diagnosis of oxygen toxicity. Diagnosis of bronchopulmonary dysplasia in newborn infants with breathing difficulties is difficult in the first few weeks.

Symptoms may include disorientation, breathing problems, and vision changes such as myopia. Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes, collapse of the alveoli in the lungs, retinal detachment, and seizures. Oxygen toxicity is managed by reducing the exposure to increased oxygen levels. Studies show that, in the long term, a robust recovery from most types of oxygen toxicity is possible.

During World War II, Donald and Yarbrough et al. performed over 2,000 experiments on oxygen toxicity to support the initial use of closed circuit oxygen rebreathers. Naval divers in the early years of oxygen rebreather diving developed a mythology about a monster called "Oxygen Pete", who lurked in the bottom of the Admiralty Experimental Diving Unit "wet pot" (a water-filled hyperbaric chamber) to catch unwary divers. They called having an oxygen toxicity attack "getting a Pete".

Acute oxygen toxicity (causing seizures, its most feared effect for divers) can occur by breathing an air mixture with 21% at or more of depth; the same thing can occur by breathing 100% at only .

This type of seizure consists of a loss of consciousness and violent muscle contractions. Signs and symptoms of oxygen toxicity are usually prevalent, but there are no standard warning signs that a seizure is about to ensue. The convulsion caused by oxygen toxicity does not lead to hypoxia, a side effect common to most seizures, because the body has an excess amount of oxygen when the convulsion begins. The seizures can lead to drowning, however, if the convulsion is suffered by a diver still in the water.

A less immediately threatening form known as pulmonary oxygen toxicity occurs after exposures to lower oxygen partial pressures for much longer periods than generally encountered in scuba diving, but is a recognised problem in saturation diving.

Likewise, divers who undergo treatment of decompression sickness are at increased risk of oxygen toxicity as treatment entails exposure to long periods of oxygen breathing under hyperbaric conditions, in addition to any oxygen exposure during the dive.

Breathing gas selected to avoid oxygen toxicity at depth, (generally below about 65 m) may be hypoxic at surface pressure or at shallow depths. There may not be any physiological warning during ascent on such a mix before loss of consciousness.

The deeper depth, called the "contingency depth", is reached when the partial pressure reaches . Diving at or beyond this level exposes the diver to a greater risk of central nervous system (CNS) oxygen toxicity. This can be extremely dangerous since its onset is often without warning and can lead to drowning, as the regulator may be spat out during convulsions, which occur in conjunction with sudden unconsciousness (general seizure induced by oxygen toxicity). Divers trained to use nitrox may memorise the acronym VENTID-C or sometimes ConVENTID, (which stands for Vision (blurriness), Ears (ringing sound), Nausea, Twitching, Irritability, Dizziness, and Convulsions).

Some gases have other dangerous effects when breathed at pressure; for example, high-pressure oxygen can lead to oxygen toxicity. Although helium is the least intoxicating of the breathing gases, at greater depths it can cause high pressure nervous syndrome, a still mysterious but apparently unrelated phenomenon. Inert gas narcosis is only one factor influencing the choice of gas mixture; the risks of decompression sickness and oxygen toxicity, cost, and other factors are also important. Because of similar and additive effects, divers should avoid sedating medications and drugs, such as cannabis and alcohol before any dive.

Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes. Historically, the central nervous system condition was called the Paul Bert effect, and the pulmonary condition the Lorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen toxicity is a concern for underwater divers, those on high concentrations of supplemental oxygen (particularly premature babies), and those undergoing hyperbaric oxygen therapy.

In individuals with chronic obstructive pulmonary disease and similar lung problems, the clinical features of oxygen toxicity are due to high carbon dioxide content in the blood (hypercapnia). This leads to drowsiness (narcosis), deranged acid-base balance due to respiratory acidosis, and death.

Hill performed research into decompression sickness, oxygen toxicity, and effects of carbon dioxide in diving. Hill advocated linear or uniform decompression profiles. This type of decompression is used today by saturation divers. His work was financed by Augustus Siebe and the Siebe Gorman Company.

Oxygen toxicity occurs when the tissues are exposed to an excessive combination of partial pressure (PPO2) and duration. In acute cases it affects the central nervous system and causes a seizure, which can result in the diver losing consciousness, spitting out their regulator and drowning. While the exact limit is not reliably predictable, and is affected by carbon dioxide levels, it is generally recognised that central nervous system oxygen toxicity is preventable if one does not exceed an oxygen partial pressure of 1.4 bar. For deep dives – generally past 180 feet (55 m), divers use "hypoxic blends" containing a lower percentage of oxygen than atmospheric air.

The shallowest stops may be done breathing pure oxygen. During prolonged decompression at high oxygen partial pressures, it may be advisable to take what is known as air breaks, where the diver switches back to a low oxygen fraction gas (usually bottom gas or travel gas) for a short period (usually about 5 minutes) to reduce the risk of developing oxygen toxicity symptoms, before continuing with the high oxygen fraction accelerated decompression. These multiple gas switches require the diver to select and use the correct demand valve and cylinder for each switch. An error of selection could compromise the decompression, or result in a loss of consciousness due to oxygen toxicity.

Although oxygen is essential to life, in concentrations significantly greater than normal it becomes toxic, overcoming the body's natural defences (antioxidants), and causing cell death in any part of the body. The lungs and brain are particularly affected by high partial pressures of oxygen, such as are encountered in diving. The body can tolerate partial pressures of oxygen around indefinitely, and up to for many hours, but higher partial pressures rapidly increase the chance of the most dangerous effect of oxygen toxicity, a convulsion resembling an epileptic seizure. Susceptibility to oxygen toxicity varies dramatically from person to person, and to a smaller extent from day to day for the same diver.

Acute, or central nervous system oxygen toxicity is a time variable response to the partial pressure exposure history of the diver and is both complex and not fully understood. Central nervous system oxygen toxicity manifests as symptoms such as visual changes (especially tunnel vision), ringing in the ears (tinnitus), nausea, twitching (especially of the face), behavioural changes (irritability, anxiety, confusion), and dizziness. This may be followed by a tonic–clonic seizure consisting of two phases: intense muscle contraction occurs for several seconds (tonic phase); followed by rapid spasms of alternate muscle relaxation and contraction producing convulsive jerking (clonic phase). The seizure ends with a period of unconsciousness (the postictal state).

Breathing 100% oxygen also eventually leads to collapse of the alveoli (atelectasis), while—at the same partial pressure of oxygen—the presence of significant partial pressures of inert gases, typically nitrogen, will prevent this effect. Preterm newborns are known to be at higher risk for bronchopulmonary dysplasia with extended exposure to high concentrations of oxygen. Other groups at higher risk for oxygen toxicity are patients on mechanical ventilation with exposure to levels of oxygen greater than 50%, and patients exposed to chemicals that increase risk for oxygen toxicity such the chemotherapeutic agent bleomycin. Therefore, current guidelines for patients on mechanical ventilation in intensive care recommends keeping oxygen concentration less than 60%.

The variability in tolerance and other variable factors such as workload have resulted in the U.S. Navy abandoning screening for oxygen tolerance. Of the 6,250 oxygen-tolerance tests performed between 1976 and 1997, only 6 episodes of oxygen toxicity were observed (0.1%). Central nervous system oxygen toxicity among patients undergoing hyperbaric oxygen therapy is rare, and is influenced by a number of a factors: individual sensitivity and treatment protocol; and probably therapy indication and equipment used. A study by Welslau in 1996 reported 16 incidents out of a population of 107,264 patients (0.015%), while Hampson and Atik in 2003 found a rate of 0.03%.

In 1988, Hamilton et al. wrote procedures for the National Oceanic and Atmospheric Administration to establish oxygen exposure limits for habitat operations. Even today, models for the prediction of pulmonary oxygen toxicity do not explain all the results of exposure to high partial pressures of oxygen.

Divers only use pure oxygen for accelerated decompression, or from oxygen rebreathers at shallow depths where the risk of acute oxygen toxicity is acceptable. Oxygen supply during in-water decompression is via rebreather, open circuit diving regulator, full-face mask or diving helmet which has been prepared for .

Reduced risk of decompression sickness, oxygen toxicity, carbon dioxide toxicity and nitrogen narcosis is dependent on a relatively high rate of pressurization and ejection from the escape lock, as all of these hazards are time-dependent. Use of a dedicated air supply further reduces risk of carbon dioxide toxicity.

Pure or nearly pure use in diving at pressures higher than atmospheric is usually limited to rebreathers, or decompression at relatively shallow depths (~6 meters depth, or less), or medical treatment in recompression chambers at pressures up to 2.8 bar, where acute oxygen toxicity can be managed without the risk of drowning. Deeper diving requires significant dilution of with other gases, such as nitrogen or helium, to prevent oxygen toxicity. People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental supplies.The reason is that increasing the proportion of oxygen in the breathing gas at low pressure acts to augment the inspired partial pressure nearer to that found at sea-level.

Exposures, from minutes to a few hours, to partial pressures of oxygen above —about eight times normal atmospheric partial pressure—are usually associated with central nervous system oxygen toxicity and are most likely to occur among patients undergoing hyperbaric oxygen therapy and divers. Since sea level atmospheric pressure is about , central nervous system toxicity can only occur under hyperbaric conditions, where ambient pressure is above normal. Divers breathing air at depths beyond face an increasing risk of an oxygen toxicity "hit" (seizure). Divers breathing a gas mixture enriched with oxygen, such as nitrox, can similarly suffer a seizure at shallower depths, should they descend below the maximum operating depth allowed for the mixture.

Oxygen is generally nontoxic, but oxygen toxicity has been reported when it is used in high concentrations. In both elemental gaseous form and as a component of water, it is vital to almost all life on earth. Despite this, liquid oxygen is highly dangerous. Even gaseous oxygen is dangerous in excess.

Oxygen toxicity is caused by exposure to oxygen at partial pressures greater than those to which the body is normally exposed. This occurs in three principal settings: underwater diving, hyperbaric oxygen therapy, and the provision of supplemental oxygen, particularly to premature infants. In each case, the risk factors are markedly different.

The use of pure oxygen for accelerated decompression is limited by oxygen toxicity. In open circuit scuba the upper limit for oxygen partial pressure is generally accepted as 1.6 bar, equivalent to a depth of 6 msw (metres of sea water), but in-water and surface decompression at higher partial pressures is routinely used in surface supplied diving operation, both by the military and civilian contractors, as the consequences of CNS oxygen toxicity are considerably reduced when the diver has a secure breathing gas supply. US Navy tables (Revision 6) start in-water oxygen decompression at 30 fsw (9 msw), equivalent to a partial pressure of 1.9 bar, and chamber oxygen decompression at 50 fsw (15 msw), equivalent to 2.5 bar.

After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away the presence of the divers. The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acute oxygen toxicity.

The associated risks are oxygen toxicity at depth and fire, particularly in the breathing apparatus. ;Hypoxic: where the oxygen content is less than that of air, generally to the extent that there is a significant risk of measurable physiological effect over the short term. The immediate risk is usually hypoxic incapacitation at or near the surface.

Oxygen is required for normal cell metabolism. Excessively high concentrations can cause oxygen toxicity such as lung damage or result in respiratory failure in those who are predisposed. Higher oxygen concentrations also increase the risk of fires, particularly while smoking, and without humidification can also dry out the nose. The target oxygen saturation recommended depends on the condition being treated.

The pulmonary condition of intoxication due to excess oxygen or oxygen toxicity is sometimes called "Lorrain Smith effect". He was elected a Fellow of the Royal Society of London on 6 May 1909. In 1919 he was elected a Fellow of the Royal Society of Edinburgh. His proposers were Sir William Turner, Cargill Gilston Knott, Sir Edmund Taylor Whittaker and Arthur Robinson.

Yildiz, Ay and Qyrdedi, in a summary of 36,500 patient treatments between 1996 and 2003, reported only 3 oxygen toxicity incidents, giving a rate of 0.008%. A later review of over 80,000 patient treatments revealed an even lower rate: 0.0024%. The reduction in incidence may be partly due to use of a mask (rather than a hood) to deliver oxygen.

Gas pressure increases with depth, rising 1 bar () every 10 meters to over 1,000 bar at the bottom of the Mariana Trench. Diving becomes more dangerous as depth increases, and deep diving presents many hazards. All surface-breathing animals are subject to decompression sickness, including aquatic mammals and free-diving humans (see taravana). Breathing at depth can cause nitrogen narcosis and oxygen toxicity.

In underwater diving activities such as saturation diving, technical diving and nitrox diving, the maximum operating depth (MOD) of a breathing gas is the depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable limit. This limit is based on risk of central nervous system oxygen toxicity, and is somewhat arbitrary, and varies depending on the diver training agency or Code of Practice, the level of underwater exertion expected and the planned duration of the dive, but is normally in the range of 1.2 to 1.6 bar. The MOD is significant when planning dives using gases such as heliox, nitrox and trimix because the proportion of oxygen in the mix determines a maximum depth for breathing that gas at an acceptable risk. There is a risk of acute oxygen toxicity if the MOD is exceeded.

Although presumed dead by support crew aboard the vessel, he was recovered by the second diver and successfully resuscitated in the bell. It has been hypothesised that his survival may have been a result of hypothermia, high partial pressure of oxygen in the bailout gas, or a combination. The ROV video footage shows him twitching while unconscious, which is consistent with an oxygen toxicity blackout.

Early reports of the disease had been made at the time of Pasley's salvage operation, but scientists were still ignorant of its causes. Early treatment methods involved returning the diver to pressurised conditions by re-immersion in the water. In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. French physiologist Paul Bert was the first to understand it as decompression sickness.

Diving much beyond is generally considered outside the scope of recreational diving. In order to dive at greater depths, as narcosis and oxygen toxicity become critical risk factors, specialist training is required in the use of various helium-containing gas mixtures such as trimix or heliox. These mixtures prevent narcosis by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium.

Oxygen toxicity is a catastrophic hazard in diving, because a seizure results in near certain death by drowning. The seizure may occur suddenly and with no warning symptoms. The effects are sudden convulsions and unconsciousness, during which victims can lose their regulator and drown. One of the advantages of a full-face diving mask is prevention of regulator loss in the event of a seizure.

Space life-support systems maintain atmospheres composed, at a minimum, of oxygen, water vapor and carbon dioxide. The partial pressure of each component gas adds to the overall barometric pressure. However, the elimination of diluent gases substantially increases fire risks, especially in ground operations when for structural reasons the total cabin pressure must exceed the external atmospheric pressure; see Apollo 1. Furthermore, oxygen toxicity becomes a factor at high oxygen concentrations.

There are risks associated with HBOT, similar to some diving disorders. Pressure changes can cause a "squeeze" or barotrauma in the tissues surrounding trapped air inside the body, such as the lungs, behind the eardrum, inside paranasal sinuses, or trapped underneath dental fillings. Breathing high-pressure oxygen may cause oxygen toxicity. Temporarily blurred vision can be caused by swelling of the lens, which usually resolves in two to four weeks.

Pulmonary hypertension can lead to tricuspid insufficiency. Excess administration of fluid causes accumulation of extracellular fluid, leading to pulmonary oedema and lack of oxygen delivery to tissues. The use of mechanical ventilation in such case can cause barotrauma, infection, and oxygen toxicity, leading to acute respiratory distress syndrome. Fluid overload also stretches the arterial endothelium, which causes damage to the glycocalyx, leading to capillary leakage and worsens the acute kidney injury.

The symptoms of narcosis may be caused by other factors during a dive: ear problems causing disorientation or nausea; early signs of oxygen toxicity causing visual disturbances; or hypothermia causing rapid breathing and shivering. Nevertheless, the presence of any of these symptoms should imply narcosis. Alleviation of the effects upon ascending to a shallower depth will confirm the diagnosis. Given the setting, other likely conditions do not produce reversible effects.

Bitterman et al. in 1986 and 1995 showed that darkness and caffeine would delay the onset of changes to brain electrical activity in rats. In the years since, research on central nervous system toxicity has centred on methods of prevention and safe extension of tolerance. Sensitivity to central nervous system oxygen toxicity has been shown to be affected by factors such as circadian rhythm, drugs, age, and gender.

If the control circuit for oxygen injection fails, the usual mode of failure results in the oxygen injection valves being closed. Unless action is taken, the breathing gas will become hypoxic with potentially fatal consequences. An alternative mode of failure is one in which the injection valves are kept open, resulting in an increasingly hyperoxic gas mix in the loop, which may pose the danger of oxygen toxicity.

Ground control states that the system detected a minor leak and began pumping pure oxygen in response. They are told to find and disconnect a yellow wire in the ceiling to disable it. Pavel passes out from oxygen toxicity, and Alexei takes control, reaching for the wire. The oxygen causes Alexei to hallucinate about his times as a young boy, running in a field, searching for a bird nest.

Cases were then seen all over the world and the cause was, at that point, unknown. By 1951 a clear link between incidence and affluence became clear: many cases were seen in developed countries with organized and well- funded health care. Two British scientists suggested that it was oxygen toxicity that caused the disease. Babies born prematurely in such affluent areas were treated in incubators which had artificially high levels of oxygen.

Pulmonary toxicity can result from longer exposure to increased oxygen levels during hyperbaric treatment. Symptoms may include disorientation, breathing problems, and vision changes such as myopia. Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes, collapse of the alveoli in the lungs, retinal detachment, and seizures. Oxygen toxicity is managed by reducing the exposure to increased oxygen levels.

The raised pressure also affects the solution of breathing gases in the tissues over time, and can lead to a range of adverse effects, such as inert gas narcosis, and oxygen toxicity. Decompression must be controlled to avoid bubble formation in the tissues and the consequent symptoms of decompression sickness. With a few exceptions, the underwater environment tends to cool the unprotected human body. This heat loss will generally lead to hypothermia eventually.

The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen below those of air, to allow the gas mix to be breathed safely on deep dives. A lower proportion of nitrogen is required to reduce nitrogen narcosis and other physiological effects of the gas at depth. Helium has very little narcotic effect. A lower proportion of oxygen reduces the risk of oxygen toxicity on deep dives.

The mixed gas must be analysed before use, as an inaccurate assumption of composition can lead to problems of hypoxia or oxygen toxicity in the case of the oxygen analysis, and decompression sickness if the inert gas components differ from the planned composition. Analysis of oxygen fraction is usually done using an electro-galvanic oxygen sensor, whereas helium fraction is usually done by a heat transfer comparison between the analysed gas and a standard sample.

To avoid oxygen toxicity and narcosis, the diver needs to plan the required mix to be blended and to check the proportions of oxygen and inert gases in the blended mix before diving. Generally the tolerance of each final component gas fraction should be within +/-1% of the required fraction. Analysis instruments commonly used by recreational/technical diving gas blenders are typically capable of a resolution of 0.1% for both oxygen and helium.

They are commonly mounted as sling cylinders, clipped to D-rings at the sides of the diver's harness. Scuba divers take great care to avoid breathing oxygen enriched "deco gas" at great depths because of the high risk of oxygen toxicity. To prevent this happening, cylinders containing oxygen- rich gases must always be positively identifiable. One way of doing this is by marking them with their maximum operating depth as clearly as possible.

The trachea is flexible enough to collapse under pressure. During deep dives, any remaining air in their bodies is stored in the bronchioles and trachea, which prevents them from experiencing decompression sickness, oxygen toxicity and nitrogen narcosis. In addition, seals can tolerate large amounts of lactic acid, which reduces skeletal muscle fatigue during intense physical activity. The main adaptations of the pinniped circulatory system for diving are the enlargement and increased complexity of veins to increase their capacity.

Hamilton was the principal investigator of the NOAA Repex Oxygen Exposure tables to assist divers in avoiding oxygen toxicity. These became the basis for most oxygen exposure calculation methods used for saturation and repetitive diving exposures to oxygen in breathing mixtures. In the late 1980s, he developed project-specific custom decompression tables. His work with decompression tables, physiological effects of gases, and methods of managing exposure to oxygen, helped to open up the new field of technical diving.

Helium has no narcotic effect, but results in HPNS when breathed at high pressures, which does not happen with gases that have greater narcotic potency. However, because of risks associated with oxygen toxicity, divers do not usually use nitrox at greater depths where more pronounced narcosis symptoms are more likely to occur. For deep diving, trimix or heliox gases are typically used; these gases contain helium to reduce the amount of narcotic gases in the mixture.

Their early work improved the prevention and treatment of decompression sickness with the inclusion of oxygen rather than air. Through World War II, work continued on decompression and oxygen toxicity. Through the 1950s NEDU tested equipment and further refined procedures for divers including the US Navy 1953 decompression table. From 1957 to 1962 was the beginnings of saturation diving under the leadership of Captain George F. Bond of the Naval Submarine Medical Research Laboratory and the Genesis Project.

If the concentration of oxygen is too lean the diver may lose consciousness due to hypoxia and if it is too rich the diver may suffer oxygen toxicity. The concentration of inert gases, such as nitrogen and helium, are planned and checked to avoid nitrogen narcosis and decompression sickness. Methods used include batch mixing by partial pressure or by mass fraction, and continuous blending processes. Completed blends are analysed for composition for the safety of the user.

These nurses must work under a supervising physician trained in hyperbarics who is available during the treatment in case of emergency. Hyperbaric nurses either join the patient inside the multiplace hyperbaric oxygen chamber or operate the machine from outside of the monoplace hyperbaric oxygen chamber, monitoring for adverse reactions to the treatment. Patients can experience adverse reactions to the hyperbaric oxygen therapy such as oxygen toxicity, hypoglycemia, anxiety, otic barotrauma, or pneumothorax. The nurse must know how to handle each adverse event appropriately.

The LARU was the first rebreather designed and built in the United States and these dives are the first closed-circuit oxygen dives in U.S. history. On one of these dives, Lambertsen experienced an episode of oxygen toxicity but managed to surface without assistance. Lake Nokomis has recently undergone a preservation project, creating areas of native vegetation along its shores. Several artificial ponds have been added to a more practical degree, as the areas where they are now were almost always flooded.

The ambient pressure underwater increases by for every of depth. The principal conditions are decompression illness (which covers decompression sickness and arterial gas embolism), nitrogen narcosis, high pressure nervous syndrome, oxygen toxicity, and pulmonary barotrauma (burst lung). Although some of these may occur in other settings, they are of particular concern during diving activities. The disorders are caused by breathing gas at the high pressures encountered at depth, and divers will often breathe a gas mixture different from air to mitigate these effects.

The signs and symptoms of diving disorders may present during a dive, on surfacing, or up to several hours after a dive. Divers have to breathe a gas which is at the same pressure as their surroundings, which can be much greater than on the surface. The ambient pressure underwater increases by for every of depth. The principal conditions are: decompression illness (which covers decompression sickness and arterial gas embolism); nitrogen narcosis; high pressure nervous syndrome; oxygen toxicity; and pulmonary barotrauma (burst lung).

A wide range of physiological factors may trigger or contribute towards a diving accident. The causes of death or serious injury in diving accidents include drowning, lung overpressure accidents, decompression sickness, carbon monoxide poisoning and trauma due to impact with boats. These are usually the final effect and may be combined, though the usually the cause of death is attributed to just one of the causes. Acute oxygen toxicity, hypoxia, hypothermia and squeezes (barotrauma) may also be primary causes of diving accidents.

This can include for low blood oxygen, carbon monoxide toxicity, cluster headaches, and to maintain enough oxygen while inhaled anesthetics are given. Long term oxygen is often useful in people with chronically low oxygen such as from severe COPD or cystic fibrosis. Oxygen can be given in a number of ways including nasal cannula, face mask, and inside a hyperbaric chamber. High concentrations of oxygen can cause oxygen toxicity such as lung damage or result in respiratory failure in those who are predisposed.

The composition of the mix must be safe for the depth and duration of the planned dive. If the concentration of oxygen is too lean the diver may lose consciousness due to hypoxia and if it is too rich the diver may suffer oxygen toxicity. The concentration of inert gases, such as nitrogen and helium, are planned and checked to avoid nitrogen narcosis and decompression sickness. Methods used include batch mixing by partial pressure or by mass fraction, and continuous blending processes.

During deep dives, any remaining air in their bodies is stored in the bronchioles and trachea, which prevents them from experiencing decompression sickness, oxygen toxicity and nitrogen narcosis. In addition, seals can tolerate large amounts of lactic acid, which reduces skeletal muscle fatigue during intense physical activity. The main adaptations of the pinniped circulatory system for diving are the enlargement and increased complexity of veins to increase their capacity. Retia mirabilia form blocks of tissue on the inner wall of the thoracic cavity and the body periphery.

Alliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic. Garlic has been used since antiquity as a therapeutic remedy for certain conditions now associated with oxygen toxicity, and, when this was investigated, garlic did indeed show strong antioxidant and hydroxyl radical-scavenging properties, it is presumed owing to the alliin contained within.

Increasing the proportion of nitrogen is not viable, since it would produce a strongly narcotic mixture. However, helium is not narcotic, and a usable mixture may be blended either by completely replacing nitrogen with helium (the resulting mix is called heliox), or by replacing part of the nitrogen with helium, producing a trimix. Pulmonary oxygen toxicity is an entirely avoidable event while diving. The limited duration and naturally intermittent nature of most diving makes this a relatively rare (and even then, reversible) complication for divers.

Recreational scuba divers commonly breathe nitrox containing up to 40% oxygen, while technical divers use pure oxygen or nitrox containing up to 80% oxygen. Divers who breathe oxygen fractions greater than of air (21%) need to be trained in the dangers of oxygen toxicity and how to prevent them. In order to buy nitrox, a diver has to show evidence of such qualification. Since the late 1990s the recreational use of oxygen has been promoted by oxygen bars, where customers breathe oxygen through a nasal cannula.

From Panama, Shilling was transferred to the Navy Diving School in Washington, DC where he learned to dive and began diving research at the Navy Experimental Diving Unit. Shilling researched the topics of nitrogen narcosis, oxygen toxicity, and decompression table development including important research on surface decompression. In the late 1930s, Shilling was transferred back to the New London Submarine Base where he focused on hearing and vision for submariners. His work involved the development of the methods and tools needed for selection of sound listening and lookout duty.

French physiologist Paul Bert was the first to understand it as DCS. His work, La Pression barométrique (1878), was a comprehensive investigation into the physiological effects of air pressure, both above and below the normal. He determined that inhaling pressurised air caused nitrogen to dissolve into the bloodstream; rapid depressurisation would then release the nitrogen into its gaseous state, forming bubbles that could block the blood circulation and potentially cause paralysis or death. Central nervous system oxygen toxicity was also first described in this publication and is sometimes referred to as the "Paul Bert effect".

As a researcher, Bennett has performed studies of nitrogen narcosis, oxygen toxicity, submarine escape, decompression illness, ascent rates, and the effects of flying after diving. Bennett first described and coined the name of high pressure nervous syndrome (HPNS), a diving disorder resulting from too much time breathing a high-pressure mixture of helium and oxygen known as heliox. Bennett was a consultant on the James Cameron underwater science fiction film The Abyss, in which a character experiences HPNS. Bennett is credited with the invention of trimix breathing gas.

Central nervous system toxicity may be referred to as the "Paul Bert effect". Pulmonary oxygen toxicity was first described by J. Lorrain Smith in 1899 when he noted central nervous system toxicity and discovered in experiments in mice and birds that had no effect but of oxygen was a pulmonary irritant. Pulmonary toxicity may be referred to as the "Lorrain Smith effect". The first recorded human exposure was undertaken in 1910 by Bornstein when two men breathed oxygen at for 30 minutes while he went on to 48 minutes with no symptoms.

In the decade following World War II, Lambertsen et al. made further discoveries on the effects of breathing oxygen under pressure and methods of prevention. Their work on intermittent exposures for extension of oxygen tolerance and on a model for prediction of pulmonary oxygen toxicity based on pulmonary function are key documents in the development of standard operating procedures when breathing increased pressures of oxygen. Lambertsen's work showing the effect of carbon dioxide in decreasing time to onset of central nervous system symptoms has influenced work from current exposure guidelines to future breathing apparatus design.

Dreyer drowned on 17 December 1994, aged 20, during a practice dive while helping a team, assembled by Nuno Gomes, set up conditions for a deep, technical dive scheduled to take place later that week. According to first- hand accounts from those diving with him, Dreyer was lost on ascent around from the surface. They conjectured he had probably lost consciousness either because of oxygen toxicity or hypercapnia induced by the high work-rate of breathing at depth. Two weeks after Dreyer's death, Theo hired a small, remotely operated sub used by the De Beers mining company.

US Navy Treatment Table 6 Evidence of the effectiveness of recompression therapy utilizing oxygen was first shown by Yarbrough and Behnke (1939), and has since become the standard of care for treatment of DCS. A typical hyperbaric oxygen treatment schedule is the US Navy Table 6, which provides for a standard treatment of 3 to 5 periods of 20 minutes of oxygen breathing at 60 fsw (18msw) followed by 2 to 4 periods of 60 minutes at 30 fsw (9 msw) before surfacing. Air breaks are taken between oxygen breathing to reduce the risk of oxygen toxicity.

Nitrox, which contains more oxygen and less nitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to about ). Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis and to avoid the risk of oxygen toxicity. This is complicated at depths beyond about , because a helium–oxygen mixture (heliox) then causes high pressure nervous syndrome. More exotic mixtures such as hydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this.

However, because of the aforementioned Henry's Law effect of extra available dissolved oxygen to neurons, there is usually no negative sequel to the event. Such seizures are generally a result of oxygen toxicity, although hypoglycemia may be a contributing factor, but the latter risk can be eradicated or reduced by carefully monitoring the person's nutritional intake prior to oxygen treatment. Oxygen first aid has been used as an emergency treatment for diving injuries for years. Recompression in a hyperbaric chamber with the person breathing 100% oxygen is the standard hospital and military medical response to decompression illness.

The raised oxygen partial pressures in the blood may also help recovery of oxygen-starved tissues downstream of the blockages. Emergency treatment for decompression illness follows schedules laid out in treatment tables. Most treatments recompress to absolute, the equivalent of of water, for 4.5 to 5.5 hours with the casualty breathing pure oxygen, but taking periodic air breaks to reduce oxygen toxicity. For serious cases resulting from very deep dives, the treatment may require a chamber capable of a maximum pressure of , the equivalent of of water, and the ability to supply heliox and nitrox as a breathing gas.

The most common side effects are flu-like symptoms and include fever, rash, dermatographism, hyperpigmentation, alopecia (hair loss), chills, and Raynaud's phenomenon (discoloration of fingers and toes). The most serious complication of bleomycin, occurring upon increasing dosage, is pulmonary fibrosis and impaired lung function. It has been suggested that bleomycin induces sensitivity to oxygen toxicity and recent studies support the role of the proinflammatory cytokines IL-18 and IL-1beta in the mechanism of bleomycin-induced lung injury. Any previous treatment with bleomycin should therefore always be disclosed to the anaesthetist prior to undergoing a procedure requiring general anaesthesia.

In the case of spacesuits, the partial pressure in the breathing gas is, in general, about 30 kPa (1.4 times normal), and the resulting partial pressure in the astronaut's arterial blood is only marginally more than normal sea-level partial pressure. Oxygen toxicity to the lungs and central nervous system can also occur in deep scuba diving and surface supplied diving. Prolonged breathing of an air mixture with an partial pressure more than 60 kPa can eventually lead to permanent pulmonary fibrosis. Exposure to an partial pressures greater than 160 kPa (about 1.6 atm) may lead to convulsions (normally fatal for divers).

Breathing pure oxygen at depths greater than can result in oxygen toxicity. Diving cylinders have also been referred to as bottles or flasks, usually preceded with the word scuba, diving, air, or bailout. Cylinders may also be called aqualungs, a genericized trademark derived from the Aqua-lung equipment made by the Aqua Lung/La Spirotechnique company, although that is more properly applied to an open circuit scuba set or open circuit diving regulator. Diving cylinders may also be specified by their application, as in bailout cylinders, stage cylinders, deco cylinders, sidemount cylinders, pony cylinders, suit inflation cylinders, etc.

Protocols for avoidance of the effects of hyperoxia exist in fields where oxygen is breathed at higher-than- normal partial pressures, including underwater diving using compressed breathing gases, hyperbaric medicine, neonatal care and human spaceflight. These protocols have resulted in the increasing rarity of seizures due to oxygen toxicity, with pulmonary and ocular damage being mainly confined to the problems of managing premature infants. In recent years, oxygen has become available for recreational use in oxygen bars. The US Food and Drug Administration has warned those suffering from problems such as heart or lung disease not to use oxygen bars.

Central nervous system oxygen toxicity manifests as symptoms such as visual changes (especially tunnel vision), ringing in the ears (tinnitus), nausea, twitching (especially of the face), behavioural changes (irritability, anxiety, confusion), and dizziness. This may be followed by a tonic–clonic seizure consisting of two phases: intense muscle contraction occurs for several seconds (tonic phase); followed by rapid spasms of alternate muscle relaxation and contraction producing convulsive jerking (clonic phase). The seizure ends with a period of unconsciousness (the postictal state). The onset of seizure depends upon the partial pressure of oxygen in the breathing gas and exposure duration.

This is followed by a slow reduction in pressure to over 30 minutes on oxygen. The patient then remains at that pressure for a further 150 minutes, consisting of two periods of 15 minutes air/60 minutes oxygen, before the pressure is reduced to atmospheric over 30 minutes on oxygen. Vitamin E and selenium were proposed and later rejected as a potential method of protection against pulmonary oxygen toxicity. There is however some experimental evidence in rats that vitamin E and selenium aid in preventing in vivo lipid peroxidation and free radical damage, and therefore prevent retinal changes following repetitive hyperbaric oxygen exposures.

In low-pressure environments oxygen toxicity may be avoided since the toxicity is caused by high partial pressure of oxygen, not merely by high oxygen fraction. This is illustrated by modern pure oxygen use in spacesuits, which must operate at low pressure (also historically, very high percentage oxygen and lower than normal atmospheric pressure was used in early spacecraft, for example, the Gemini and Apollo spacecraft). In such applications as extra- vehicular activity, high-fraction oxygen is non-toxic, even at breathing mixture fractions approaching 100%, because the oxygen partial pressure is not allowed to chronically exceed .

Skilled sidemount exponents can carry 6 aluminum 80 cylinders this way, 3 each side. The diver must be able to positively identify the gas supplied by any one of the several demand valves that these configurations require, to avoid potentially fatal problems of oxygen toxicity, hypoxia, nitrogen narcosis or divergence from the decompression plan which may occur if an inappropriate gas is used. One of the conventions puts the oxygen rich gases to the right, Other methods include labelling by content and/or maximum operating depth (MOD), and identification by touch. Often several or all of these methods are used together.

Oxygen rebreathers are simple and reliable due to the simplicity. The gas mixture is known and reliable providing the loop is adequately flushed at the start of a dive and the correct gas is used. There is little that can go wrong with the function other than flooding, leaking and running out of gas, both of which are obvious to the user, and there is no risk of decompression sickness, so emergency free ascent to the surface is always an option in open water. The critical limitation of the oxygen rebreather is the very shallow depth limit, due to oxygen toxicity considerations.

Doolette and Mitchell propose that a switch from a helium-rich mix to a nitrogen-rich mix, as is common in technical diving when switching from trimix to nitrox on ascent, may cause a transient supersaturation of inert gas within the inner ear and result in IEDCS. They suggest that breathing-gas switches from helium-rich to nitrogen-rich mixtures should be carefully scheduled either deep (with due consideration to nitrogen narcosis) or shallow to avoid the period of maximum supersaturation resulting from the decompression. Switches should also be made during breathing of the largest inspired oxygen partial pressure that can be safely tolerated with due consideration to oxygen toxicity.

Typical breathing effort when breathing through a diving regulator Pressure increases with the depth of water at the rate of about one atmosphere — slightly more than 100 kPa, or one bar, for every 10 meters. Air breathed underwater by divers is at the ambient pressure of the surrounding water and this has a complex range of physiological and biochemical implications. If not properly managed, breathing compressed gasses underwater may lead to several diving disorders which include pulmonary barotrauma, decompression sickness, nitrogen narcosis, and oxygen toxicity. The effects of breathing gasses under pressure are further complicated by the use of one or more special gas mixtures.

If the diver is to work at fairly constant depths for periods which would require long periods for decompression, the diver may live in a special underwater habitat or a pressurised surface habitat called a saturation system. This type of diving is known as saturation diving. The same technique for supplying breathing gas as regular surface supplied diving is used, with the diving bell receiving breathing gas and other essential services from a diving support vessel on the surface. If diving at extreme depths, helium-based breathing gas mixtures are used to prevent nitrogen narcosis and oxygen toxicity which would otherwise occur due to the high ambient pressure.

Although some of these may occur in other settings, they are of particular concern during diving activities. The disorders are caused by breathing gas at the high pressures encountered at depth, and divers will often breathe a gas mixture different from air to mitigate these effects. Nitrox, which contains more oxygen and less nitrogen is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to about ). Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis and to avoid the risk of oxygen toxicity.

Scuba divers cannot accept a high risk of oxygen toxicity convulsions and would usually consider an oxygen partial pressure of 1.6 bar to be the upper limit, though exposure at this pressure is likely to be of very short duration if an immediate ascent is started. It is common practice to use a non-optimised gas, as emergencies are not expected, and the same gas may be carried on several dives, as long as the remaining quantity is sufficient. The Diving Medical Advisory Council has more recently (2016) made a more conservative recommendation of an oxygen partial pressure for open circuit bailout for saturation divers of between 1.4 and 0.4 bar.

If compressed air is used, then an oxygen mask or hood is needed as in a multiplace chamber. Most monoplace chambers can be fitted with a demand breathing system for air breaks. In low pressure soft chambers, treatment schedules may not require air breaks, because the risk of oxygen toxicity is low due to the lower oxygen partial pressures used (usually 1.3 ATA), and short duration of treatment. For alert, cooperative patients, air breaks provided by mask are more effective than changing the chamber gas because they provide a quicker gas change and a more reliable gas composition both during the break and treatment periods.

Emergency HBOT for decompression illness follows treatment schedules laid out in treatment tables. Most cases employ a recompression to absolute, the equivalent of of water, for 4.5 to 5.5 hours with the casualty breathing pure oxygen, but taking air breaks every 20 minutes to reduce oxygen toxicity. For extremely serious cases resulting from very deep dives, the treatment may require a chamber capable of a maximum pressure of , the equivalent of of water, and the ability to supply heliox as a breathing gas. U.S. Navy treatment charts are used in Canada and the United States to determine the duration, pressure, and breathing gas of the therapy.

Hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (O2) or higher than normal partial pressure of oxygen. In medicine, it refers to excess oxygen in the lungs or other body tissues, which can be caused by breathing air or oxygen at pressures greater than normal atmospheric pressure. This kind of hyperoxia can lead to oxygen toxicity, caused from the harmful effects of breathing molecular oxygen at elevated partial pressures. Hyperoxia is the opposite of hypoxia; hyperoxia refers to a state in which oxygen supply is excessive, and hypoxia refers to a state in which oxygen supply is insufficient.

At partial pressures of oxygen of —100% oxygen at 2 to 3 times atmospheric pressure—these symptoms may begin as early as 3 hours after exposure to oxygen. Experiments on rats breathing oxygen at pressures between suggest that pulmonary manifestations of oxygen toxicity may not be the same for normobaric conditions as they are for hyperbaric conditions. Evidence of decline in lung function as measured by pulmonary function testing can occur as quickly as 24 hours of continuous exposure to 100% oxygen, with evidence of diffuse alveolar damage and the onset of acute respiratory distress syndrome usually occurring after 48 hours on 100% oxygen.

Rapid and uncontrolled depth changes can seriously endanger the diver. An uncontrolled ascent can lead to decompression illness, and uncontrolled descent can take the diver to a depth where the equipment and breathing gas are not appropriate, and can cause debilitating narcosis, acute oxygen toxicity, barotraumas of descent, rapid exhaustion of breathing gas supplies, excessive work of breathing, and inability to surface. These effects can be caused by failures of weighting and buoyancy control equipment. Surface-supplied divers may avoid these problems in many cases by using a bell or stage for vertical travel through the water, but scuba divers need to be appropriately buoyant at all times when in the water.

In tropical and sub-tropical parts of the world, there is a large market for 'holiday divers'; people who train and dive while on holiday, but rarely dive close to home. Technical diving and the use of rebreathers are increasing, particularly in areas of the world where deeper wreck diving is the main underwater attraction. Generally, recreational diving depths are limited by the training agencies to a maximum of between 30 and 40 meters (100 and 130 feet), beyond which a variety of safety issues such as oxygen toxicity and nitrogen narcosis significantly increase the risk of diving using recreational diving equipment and practices, and specialized skills and equipment for technical diving are needed.

Breathing gas density can be reduced by using helium as the basic component, with sufficient oxygen added to suit the circumstances and retain a partial pressure sufficient to sustain consciousness but not so much as to cause oxygen toxicity problems. Frictional resistance to flow is influenced by the shape and size of the gas passages, and the pressure, density, viscosity, and velocity of the gas. Valve cracking pressure is a factor of design and settings of the valve mechanisms. The breathing performance of regulators assumes gas density is specified and measures the resistance to flow during the full breathing cycle with a given volumetric flow rate as a pressure drop between the mouthpiece and the exterior environment.

The increased partial pressure of oxygen due to the higher oxygen content of nitrox increases the risk of oxygen toxicity, which becomes unacceptable below the maximum operating depth of the mixture. To displace nitrogen without the increased oxygen concentration, other diluent gases can be used, usually helium, when the resultant three gas mixture is called trimix, and when the nitrogen is fully substituted by helium, heliox. For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as Travel, Bottom, and Decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.

If the diver is to work at fairly constant depths for periods which would require long periods for decompression, the diver may temporarily live in a pressurised surface habitat called a saturation system, and be transported under pressure in a closed bell to and from the underwater workplace. This type of diving is known as saturation diving. The same techniques for supplying breathing gas are used as in surface oriented surface-supplied diving, with the diving bell receiving breathing gas and other essential services from the surface. If diving at extreme depths, helium-based breathing gas mixtures are used to prevent nitrogen narcosis and oxygen toxicity which would otherwise occur due to the high ambient pressure.

High-flow therapy has shown to be useful in neonatal intensive care settings for premature infants with Infant respiratory distress syndrome, as it prevents many infants from needing artificial ventilation via intubation, and allows safe respiratory management at lower FiO2 levels, and thus reduces the risk of retinopathy of prematurity and oxygen toxicity. Due to the decreased stress of effort needed to breathe, the neonatal body is able to spend more time utilizing metabolic efforts elsewhere, which causes decreased days on a mechanical ventilator, faster weight gain, and overall decreased hospital stay entirely. High flow therapy has been successfully implemented in infants and older children. The cannula improves the respiratory distress, the oxygen saturation, and the patient's comfort.

Nitrox is used to a lesser extent in surface-supplied diving, as these advantages are reduced by the more complex logistical requirements for nitrox compared to the use of simple low-pressure compressors for breathing gas supply. Nitrox can also be used in hyperbaric treatment of decompression illness, usually at pressures where pure oxygen would be hazardous. Nitrox is not a safer gas than compressed air in all respects; although its use can reduce the risk of decompression sickness, it increases the risk of oxygen toxicity and fire. Though not generally referred to as nitrox, an oxygen-enriched air mixture is routinely provided at normal surface ambient pressure as oxygen therapy to patients with compromised respiration and circulation.

NEDU divers were essential to the recovery of artifacts from the wreck of the USS Monitor in 2001 and 2002. In 2002, certification of the Mark 16 Mod 1 rebreather was completed following improvement of systems including, extension of the working limit to , new decompression tables for both nitrogen-oxygen and helium-oxygen diving including new repetitive diving capabilities for helium-oxygen, test of an Emergency Breathing System with communications, the addition of an integrated buoyancy compensation device, and an improved full face mask. SEALs using SEAL Delivery Vehicle In 2004, NEDU contributed to operational guidance for diving in harsh contaminated environments. NEDU has continued research into oxygen toxicity utilizing the US Navy Mark 16 Mod 1.

Lowering the oxygen content increases the maximum operating depth and duration of the dive before which oxygen toxicity becomes a limiting factor. Most trimix divers limit their working oxygen partial pressure [PO2] to 1.4 bar and may reduce the PO2 further to 1.3 bar or 1.2 bar depending on the depth, the duration and the kind of breathing system used. A maximum oxygen partial pressure of 1.4 bar for the active sectors of the dive, and 1.6 bar for decompression stops is recommended by several recreational and technical diving certification agencies for open circuit, and 1.2 bar or 1.3 bar as maximum for the active sectors of a dive on closed circuit rebreather.

The increased partial pressure of oxygen due to the higher oxygen content of nitrox increases the risk of oxygen toxicity, which becomes unacceptable below the maximum operating depth of the mixture. To displace nitrogen without the increased oxygen concentration, other diluent gases can be used, usually helium, when the resultant three gas mixture is called trimix, and when the nitrogen is fully substituted by helium, heliox. For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as Travel, Bottom, and Decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.

His classical work, La Pression barometrique (1878), was a comprehensive investigation into the physiological effects of air-pressure, both above and below the normal. He determined that inhaling pressurized air caused the nitrogen to dissolve into the bloodstream; rapid depressurization would then release the nitrogen into its natural gaseous state, forming bubbles that could block the blood circulation and potentially cause paralysis or death. Central nervous system oxygen toxicity was also first described in this publication and is sometimes referred to as the "Paul Bert effect". John Scott Haldane designed a decompression chamber in 1907 to help make deep-sea divers safer and he produced the first decompression tables for the Royal Navy in 1908 after extensive experiments with animals and human subjects.

To dive safely with nitrox, the diver must learn good buoyancy control, a vital part of scuba diving in its own right, and a disciplined approach to preparing, planning and executing a dive to ensure that the ppO2 is known, and the maximum operating depth is not exceeded. Many dive shops, dive operators, and gas blenders (individuals trained to blend gases) require the diver to present a nitrox certification card before selling nitrox to divers. Some training agencies, such as PADI and Technical Diving International, teach the use of two depth limits to protect against oxygen toxicity. The shallower depth is called the "maximum operating depth" and is reached when the partial pressure of oxygen in the breathing gas reaches .

In 1906, Schrötter suggested the use of oxygen with recompression, but concerns over oxygen toxicity kept the suggestion from becoming the standard practice that it is today. He was interested in the physiological effects that divers experienced when ascending from ocean depths, as well as the effects that higher altitudes placed upon balloonists and mountain climbers. On 31 July 1901 meteorologists Arthur Berson (1859–1942) and Reinhard Süring (1866–1950) aboard the balloon Preussen, and equipped with portable compressed oxygen containers, were able to reach 10,800 meters above sea level. However, at 10,000 meters the two scientists succumbed to unconsciousness, and from this experiment Schrötter realized that even 100% oxygen would be an insufficient safeguard against hypoxia at very high altitudes.

To minimize the requirement for venting, oxygen-rich treatment gases are usually provided to the patient by built in breathing system (BIBS) masks, which vent exhaled gas outside the chamber. BIBS masks are provided with straps to hold them in place over the mouth and nose, but are often held in place manually, so they will fall away if the user has an oxygen toxicity convulsion. BIBS masks provide gas on demand (inhalation), much like a diving regulator, and use a similar system to control outflow to the normobaric environment. They are connected to supply lines plumbed through the pressure hull of the chamber, valved on both sides, and supplied from banks of storage cylinders, usually kept near the chamber.

The underwater environment presents a constant hazard of asphyxiation due to drowning. Breathing apparatus used for diving is life-support equipment, and failure can have fatal consequences – reliability of the equipment and the ability of the diver to deal with a single point of failure are essential for diver safety. Failure of other items of diving equipment is generally not as immediately threatening, as provided the diver is conscious and breathing, there may be time to deal with the situation, however an uncontrollable gain or loss of buoyancy can put the diver at severe risk of decompression sickness, or of sinking to a depth where nitrogen narcosis or oxygen toxicity may render the diver incapable of managing the situation, which may lead to drowning while breathing gas remains available.

Oxygen rebreathers are severely depth limited due to oxygen toxicity risk, which increases with depth, and the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets. The first commercially practical scuba rebreather was designed and built by the diving engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. His self contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with an estimated 50–60% oxygen supplied from a copper tank and carbon dioxide scrubbed by passing it through a bundle of rope yarn soaked in a solution of caustic potash. During the 1930s and all through World War II, the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the first frogmen.

Divers breathing oxygen in the chamber after a dive Surface decompression is a procedure in which some or all of the staged decompression obligation is done in a decompression chamber instead of in the water. This reduces the time that the diver spends in the water, exposed to environmental hazards such as cold water or currents, which will enhance diver safety. The decompression in the chamber is more controlled, in a more comfortable environment, and oxygen can be used at greater partial pressure as there is no risk of drowning and a lower risk of oxygen toxicity convulsions. A further operational advantage is that once the divers are in the chamber, new divers can be supplied from the diving panel, and the operations can continue with less delay.

Several common types of dive profile are specifically named, and these may be characteristic of the purpose of the dive. For example, a working dive at a limited location will often follow a constant depth (square) profile, and a recreational dive is likely to follow a multilevel profile, as the divers start deep and work their way up a reef to get the most out of the available breathing gas. The names are usually descriptive of the graphic appearance. The intended dive profile is useful as a planning tool as an indication of the risks of decompression sickness and oxygen toxicity for the exposure, and also for estimating the volume of open-circuit breathing gas needed for a planned dive, as these depend in part upon the depth and duration of the dive.

High pressure nervous syndrome affects divers breathing helium mixes during rapid compression to high pressures, Compression arthralgia can also affect divers during rapid compression to high pressures. Long decompression times can be reduced by higher oxygen content of breathing gas, but this can expose the diver to oxygen toxicity effects, and changing from helium to nitrogen diluted gases during decompression can cause isobaric counterdiffusion problems. Toxicity of breathing gas contaminants is proportional to partial pressure, and a gas which may have no effect at the surface can be dangerously toxic at higher ambient pressure. Hypoxia of ascent can affect freedivers and rebreather divers, and in occasional circumstances scuba and surface-supplied divers, and can be a killer, as the diver can lose consciousness without warning and consequently drown or asphyxiate.

Divers breathing oxygen in the chamber after a dive Surface decompression is a procedure in which some or all of the staged decompression obligation is done in a decompression chamber instead of in the water. This reduces the time that the diver spends in the water, exposed to environmental hazards such as cold water or currents, which will enhance diver safety. The decompression in the chamber is more controlled, in a more comfortable environment, and oxygen can be used at greater partial pressure as there is no risk of drowning and a lower risk of oxygen toxicity convulsions. A further operational advantage is that once the divers are in the chamber, new divers can be supplied from the diving panel, and the operations can continue with less delay.

Nasal cannulas provide inspired oxygen fractions only slightly more than air, and are not of much benefit to injured divers. Air breaks are not necessary to avoid oxygen toxicity at surface pressure. ;Emergency oxygen supply: Sufficient oxygen to provide two divers with 100% oxygen at 15 litres per minute for long enough to reach further supplies of oxygen is standard equipment for commercial diving operations under the Scientific and Inshore codes of Practice in South Africa. ;Extrication and transportation equipment: An injured diver may need to be removed from the water in an inconvenient place, and special equipment such as a stretcher, spine board, high-angle rescue equipment or recovery slings may be required to get the casualty to a place more suitable for first aid, or to a vehicle for transportation to medical facilities.

High {P_{a_{CO_2}}} triggers the fight or flight response, affects hormone levels and can cause anxiety, irritability and inappropriate or panic responses, which can be beyond the control of the subject, sometimes with little or no warning. Vasodilation is another effect, notably in the skin, where feelings of unpleasant heat are reported, and in the brain, where blood flow can increase by 50% at a {P_{ET_{CO_2}}} of , Intracranial pressure may rise, with a throbbing headache. If associated with a high {P_{a_{CO_2}}} the high delivery of oxygen to the brain may increase the risk of CNS oxygen toxicity at partial pressures usually considered acceptable. In many people a high {P_{a_{CO_2}}} causes a feeling of shortness of breath, but the lack of this symptom is no guarantee that the other effects are not occurring.

This depth is the theoretical maximum which can be safely attained with any two-component argon/oxygen mix: a larger fraction of oxygen than about 50% will result in oxygen toxicity before this depth, and a larger fraction of argon than about 50% will result in argon narcosis before this depth. However, as argox is more narcotic than nitrogen (causing it to be more dangerous if a decompression mix is accidentally breathed), and because argox is moderately more expensive than nitrox, and mostly because there has been little research done into the actual (vs. theoretical) physiological aspects of breathing argon during decompression, argox is not currently recommended by any professional agency for this purpose. Although there is little research relating to divers decompressing using argon mixes, there have been scientific studies of astronauts decompressing using argox.

Recompression treatment in a hyperbaric chamber was initially used as a life-saving tool to treat decompression sickness in caisson workers and divers who stayed too long at depth and developed decompression sickness. Now, it is a highly specialized treatment modality that has been found to be effective in the treatment of many conditions where the administration of oxygen under pressure has been found to be beneficial. Studies have shown it to be quite effective in some 13 indications approved by the Undersea and Hyperbaric Medical Society. Hyperbaric oxygen treatment is generally preferred when effective, as it is usually a more efficient and lower risk method of reducing symptoms of decompression illness, but in some cases recompression to pressures where oxygen toxicity is unacceptable may be required to eliminate the bubbles in the tissues in severe cases of decompression illness.

They may be rated for lower pressures if not primarily intended for treatment of diving injuries. A recompression chamber for a single diving casualty In the larger multiplace chambers, patients inside the chamber breathe from either "oxygen hoods" – flexible, transparent soft plastic hoods with a seal around the neck similar to a space suit helmet – or tightly fitting oxygen masks, which supply pure oxygen and may be designed to directly exhaust the exhaled gas from the chamber. During treatment patients breathe 100% oxygen most of the time to maximise the effectiveness of their treatment, but have periodic "air breaks" during which they breathe chamber air (21% oxygen) to reduce the risk of oxygen toxicity. The exhaled treatment gas must be removed from the chamber to prevent the buildup of oxygen, which could present a fire risk.

A recompression chamber for a single diving casualty In the larger multiplace chambers, patients inside the chamber breathe from either "oxygen hoods" – flexible, transparent soft plastic hoods with a seal around the neck similar to a space suit helmet – or tightly fitting oxygen masks, which supply pure oxygen and may be designed to directly exhaust the exhaled gas from the chamber. During treatment patients breathe 100% oxygen most of the time to maximise the effectiveness of their treatment, but have periodic "air breaks" during which they breathe chamber air (21% oxygen) to reduce the risk of oxygen toxicity. The exhaled treatment gas must be removed from the chamber to prevent the buildup of oxygen, which could present a fire risk. Attendants may also breathe oxygen some of the time to reduce their risk of decompression sickness when they leave the chamber.

Recompression treatment in a hyperbaric chamber was initially used as a life-saving tool to treat decompression sickness in caisson workers and divers who stayed too long at depth and developed decompression sickness. Now, it is a highly specialized treatment modality that has been found to be effective in the treatment of many conditions where the administration of oxygen under pressure has been found to be beneficial. Studies have shown it to be quite effective in some 13 indications approved by the Undersea and Hyperbaric Medical Society. Hyperbaric oxygen treatment is generally preferred when effective, as it is usually a more efficient and lower risk method of reducing symptoms of decompression illness, However, in some cases recompression to pressures where oxygen toxicity is unacceptable may be required to eliminate the bubbles in the tissues that cause the symptoms.

Many nitrox-capable dive computers calculate an oxygen loading and can track it across multiple dives. The aim is to avoid activating the alarm by reducing the partial pressure of oxygen in the breathing gas or by reducing the time spent breathing gas of greater oxygen partial pressure. As the partial pressure of oxygen increases with the fraction of oxygen in the breathing gas and the depth of the dive, the diver obtains more time on the oxygen clock by diving at a shallower depth, by breathing a less oxygen-rich gas, or by shortening the duration of exposure to oxygen-rich gases. Diving below on air would expose a diver to increasing danger of oxygen toxicity as the partial pressure of oxygen exceeds , so a gas mixture must be used which contains less than 21% oxygen (a hypoxic mixture).

He was also involved in many clinical trials conducted in India. Sharma has presented papers at 229 national and international conferences including the first international meeting on Light and Oxygen Toxicity to the Eye and has a scientific exhibit displayed at the American Academy of Ophthalmology. He was an invited guest speaker at the Annual Conference of American Academy of Ophthalmology, San Francisco in 2006 and 2009 where he delivered lectures on Minimally Invasive Vitreous Surgery: Sutureless 20, 23 and 25 Gauge System, Silicon Oil in Vitreo-Retinal Surgery and Wide Angle Vitreous Surgery. He is a peer reviewer for many international scientific journals and publications such as American Journal of Ophthalmology, Indian Journal of Ophthalmology, British Journal of Medical Groups, British Journal of Ophthalmology, Paediatric Ophthalmology and Strabismus 2010 and has been the chief editor of Jaypee's Video Atlas of Vitreo-Retinal Surgery (with 12 DVD Roms).

There will be a mixture known as the bottom gas, which is optimised for limiting inert gas narcosis and oxygen toxicity during the deep sector of the dive. This is generally the mixture which is needed in the largest amount for open circuit diving, as the consumption rate will be greatest at maximum depth. The oxygen fraction of the bottom gas suitable for a dive deeper than about will not have sufficient oxygen to reliably support consciousness at the surface, so a travel gas must be carried to start the dive and get down to the depth at which the bottom gas is appropriate. There is generally a large overlap of depths where either gas can be used, and the choice of the point at which the switch will be made depends on considerations of cumulative toxicity, narcosis and gas consumption logistics specific to the planned dive profile.

The emergency gas supply must support life at any depth where it is likely to be used. It will almost always be used for ascent or return to the bell, so a relatively oxygen-rich mixture will usually be advantageous. In closed bell diving an unusually high oxygen partial pressure of 2.8 bar as used in therapeutic decompression was recommended by Association of Offshore Diving Contractors (AODC) and endorsed by the Diving Medical Advisory Council (DMAC) on the assumption that if the diver does not make it back into the bell on the bailout gas, or loses consciousness to acute oxygen toxicity, the chances of successful resuscitation will be better than in the case of hypoxia. This strategy only holds when bailout is at constant pressure, the diver's airway is secured by a helmet, and there is a bellman to assist, as the risk of losing consciousness is relatively high.

Although the convulsions caused by central nervous system oxygen toxicity may lead to incidental injury to the victim, it remained uncertain for many years whether damage to the nervous system following the seizure could occur and several studies searched for evidence of such damage. An overview of these studies by Bitterman in 2004 concluded that following removal of breathing gas containing high fractions of oxygen, no long-term neurological damage from the seizure remains. The majority of infants who have survived following an incidence of bronchopulmonary dysplasia will eventually recover near-normal lung function, since lungs continue to grow during the first 5–7 years and the damage caused by bronchopulmonary dysplasia is to some extent reversible (even in adults). However, they are likely to be more susceptible to respiratory infections for the rest of their lives and the severity of later infections is often greater than that in their peers.

Bank of oxygen cylinders for recompression treatment or surface decompression Originally therapeutic recompression was done using air as the only breathing gas, and this is reflected in several of the tables detailed below. However work by Yarbrough and Behnke showed that use of oxygen as a treatment gas is usually beneficial and this has become the standard of care for treatment of DCS. Pure oxygen can be used at pressures up to 60 fsw (18 msw) with acceptable risk of CNS oxygen toxicity, which generally has acceptable consequences in the chamber environment when an inside tender is at hand. At greater pressures, treatment gas mixtures using Nitrogen or Helium as a diluent to limit partial pressure of oxygen to 3 ata (3& bar) or less are preferred to air as they are more effective both at elimination of inert gases and oxygenating injured tissues in comparison with air.

In the U.S. Major Christian J. Lambertsen invented a free-swimming oxygen rebreather. In 1952 he patented a modification of his apparatus, this time named SCUBA, an acronym for "self- contained underwater breathing apparatus," which became the generic English word for autonomous breathing equipment for diving, and later for the activity using the equipment. After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away the presence of the divers. The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acute oxygen toxicity. Although a working demand regulator system had been invented in 1864 by Auguste Denayrouze and Benoît Rouquayrol, the first open-circuit scuba system developed in 1925 by Yves Le Prieur in France was a manually adjusted free-flow system with a low endurance, which limited the practical usefulness of the system.

The Sea Link and Sea Diver crews considered whether to use the submersible's lockout capacity to allow one of the men in the diving compartment to exit the submersible and attempt to free it from the cable. This plan was abandoned because it posed a danger of oxygen toxicity to Link and Stover in the diving chamber. The Sea Link crew and Edwin Link, who was in overall charge of the situation, agreed to await the Tringas arrival. Levels of carbon dioxide (CO2) began to rise in the pilot compartment when the CO2 scrubber failed. Menzies took off his shirt, emptied the carbon dioxide absorbent Baralyme from the scrubber canister into it and held it in front of the circulating fans of the air conditioning unit, lowering the CO2 level in the pilot's cabin. The Sea Diver crew calculated that the CO2 in the submersible could be maintained at acceptable levels for 42 hours in the pilot compartment and 61 hours in the diver compartment.

By the turn of the twentieth century, two basic architectures for underwater breathing apparatus had been pioneered; open-circuit surface supplied equipment where the diver's exhaled gas is vented directly into the water, and closed-circuit breathing apparatus where the diver's carbon dioxide is filtered from unused oxygen, which is then recirculated. Closed circuit equipment was more easily adapted to scuba in the absence of reliable, portable, and economical high pressure gas storage vessels. By the mid twentieth century, high pressure cylinders were available and two systems for scuba had emerged: open-circuit scuba where the diver's exhaled breath is vented directly into the water, and closed- circuit scuba where the carbon dioxide is removed from the diver's exhaled breath which has oxygen added and is recirculated. Oxygen rebreathers are severely depth-limited due to oxygen toxicity risk, which increases with depth, and the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets.

The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acute oxygen toxicity. Although a working demand regulator system had been invented in 1864 by Auguste Denayrouze and Benoît Rouquayrol, the first open-circuit scuba system developed in 1925 by Yves Le Prieur in France was a manually adjusted free-flow system with a low endurance, which limited its practical usefulness. In 1942, during the German occupation of France, Jacques-Yves Cousteau and Émile Gagnan designed the first successful and safe open-circuit scuba, known as the Aqua-Lung. Their system combined an improved demand regulator with high-pressure air tanks. This was patented in 1945. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed to the U.S. Divers company, and in 1948 to Siebe Gorman of England.

The term "nitrox" was originally used to refer to the breathing gas in a seafloor habitat where the oxygen has to be kept to a lower fraction than in air to avoid long term oxygen toxicity problems. It was later used by Dr Morgan Wells of NOAA for mixtures with an oxygen fraction higher than air, and has become a generic term for binary mixtures of nitrogen and oxygen with any oxygen fraction, and in the context of recreational and technical diving, now usually refers to a mixture of nitrogen and oxygen with more than 21% oxygen. "Enriched Air Nitrox" or "EAN", and "Oxygen Enriched Air" are used to emphasize richer than air mixtures. In "EANx", the "x" was originally the x of nitrox, but has come to indicate the percentage of oxygen in the mix and is replaced by a number when the percentage is known; for example, a 40% oxygen mix is called EAN40.

As there is an increased risk of central nervous system oxygen toxicity on deep dives, long dives and dives where oxygen-rich breathing gases are used, divers are taught to calculate a maximum operating depth for oxygen-rich breathing gases, and cylinders containing such mixtures must be clearly marked with that depth. In some diver training courses for these types of diving, divers are taught to plan and monitor what is called the oxygen clock of their dives. This is a notional alarm clock, which ticks more quickly at increased oxygen pressure and is set to activate at the maximum single exposure limit recommended in the National Oceanic and Atmospheric Administration Diving Manual. For the following partial pressures of oxygen the limits are: 45 minutes at , 120 minutes at , 150 minutes at , 180 minutes at and 210 minutes at , but it is impossible to predict with any reliability whether or when toxicity symptoms will occur.

A diver in a pool wearing an AGA full face mask A diver wearing an Ocean Reef full face mask Head protection helmet for use with Ocean Reef full face diving mask A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece, demand valve or constant flow gas supply that provides the diver with breathing gas. The full face mask has several functions: it lets the diver see clearly underwater, it provides the diver's face with some protection from cold and polluted water and from stings, such as from jellyfish or coral. It increases breathing security and provides a space for equipment that lets the diver communicate with the surface support team. Full-face masks can be more secure than breathing from an independent mouthpiece; if the diver becomes unconscious or suffers an oxygen toxicity convulsion, the diver can continue to breathe from the mask, unlike a scuba mouthpiece which is normally gripped between the teeth.

One of the more frequently used treatment schedules is the US Navy Table 6, which provides hyperbaric oxygen therapy with a maximum pressure equivalent to of seawater for a total time under pressure of 288 minutes, of which 240 minutes are on oxygen and the balance are air breaks to minimise the possibility of oxygen toxicity. A multiplace chamber is the preferred facility for treatment of decompression sickness as it allows direct physical access to the patient by medical personnel, but monoplace chambers are more widely available and should be used for treatment if a multiplace chamber is not available or transportation would cause significant delay in treatment, as the interval between onset of symptoms and recompression is important to the quality of recovery. It may be necessary to modify the optimum treatment schedule to allow use of a monoplace chamber, but this is usually better than delaying treatment. A US Navy treatment table 5 can be safely performed without air breaks if a built-in breathing system is not available.

The breathing gas mixture in a diving rebreather loop is usually measured using oxygen cells, and the output of the cells is used by either the diver or an electronic control system to control addition of oxygen to increase partial pressure when it is below the chosen lower set-point, or to flush with diluent gas when it is above the upper set-point. When the partial pressure is between the upper and lower set- points, it is suitable for breathing at that depth and is left until it changes as a result of consumption by the diver, or a change in ambient pressure as a result of a depth change. Accuracy and reliability of measurement is important in this application for two basic reasons. Firstly, if the oxygen content is too low, the diver will lose consciousness due to hypoxia and probably die, or if the oxygen content is too high, the risk of central nervous system oxygen toxicity causing convulsions and loss of consciousness, with a high risk of drowning becomes unacceptable.

Surface supplied divers may be required to work at maximum depth for longer and the partial pressure of oxygen may be limited to reduce pulmonary oxygen toxicity, so the discrepancy in oxygen content when surfacing may be greater, however in this case gas switching is controlled by the surface personnel, and the diver's airway is protected by the full-face mask or helmet, and the surface personnel can monitor the status of the diver on the voice communications system, so the overall risk is reduced in comparison with scuba. ;Rebreather diving: During ascent at a rate where oxygen addition to the loop does not adequately compensate for partial pressure reduction due to decreasing ambient pressure, the oxygen concentration in the breathing loop can drop below the level required to support consciousness. ;Freediving: During breath-hold diving there is no additional breathing gas available during the ascent. If the diver stays down long enough to use up the available oxygen to the extent where tissue concentration has dropped below a level sufficient to support consciousness at surface pressure, there is a very high risk of blackout before the surface can be reached.