Nitrogen narcosis

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Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect), is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις (narcosis) is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates.[2] Narcosis produces a state similar to alcohol intoxication or nitrous oxide inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 meters (100 ft).

Apart from helium, and probably neon, all gases that can be breathed have a narcotic effect, which is greater as the lipid solubility of the gas increases.[3] As depth increases, the effects may become hazardous as the diver is increasingly impaired. Although divers can learn to cope with the effects, it is not possible to develop a tolerance. While narcosis affects all divers, predicting the depth at which narcosis will affect a diver is difficult, as susceptibility varies widely from dive to dive and amongst individuals.

The condition is completely reversed by ascending to a shallower depth with no long-term effects. For this reason, narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms and ascend to manage it. Diving beyond 40 m (130 ft) is considered outside the scope of recreational diving: as narcosis and oxygen toxicity become critical factors, specialist training is required in the use of various gas mixtures such as trimix or heliox.

Contents

Classification

Narcosis results from breathing gases under elevated pressure and may be classified by the principal gas involved. The noble gases, except helium and probably neon,[3] as well as nitrogen, oxygen and hydrogen cause a decrement in mental function, but their effect on psychomotor function (processes affecting the coordination of sensory or cognitive processes and motor activity) varies widely. The effects of carbon dioxide consistently result in a decrease of both mental and psychomotor function.[4] The noble gases argon, krypton, and xenon are more narcotic than nitrogen at a given pressure, and xenon has so much anesthetic activity that it is actually a usable anesthetic at 80% concentration and normal atmospheric pressure. Xenon has historically been too expensive to be used very much in practice, but it has been successfully used for surgical operations, and xenon anesthesia systems are still being proposed and designed.[5]

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