Nevertheless, the severity of narcosis is unpredictable and it can be fatal while diving, as the result of illogical behavior in a dangerous environment.Tests have shown that all divers are affected by nitrogen narcosis, though some experience lesser effects than others. Even though it is possible that some divers can manage better than others because of learning to cope with the subjective impairment, the underlying behavioral effects remain. These effects are particularly dangerous because a diver may feel they are not experiencing narcosis, yet still be affected by it. History
French researcher Victor T. Junod was the first to describe symptoms of narcosis in 1834, noting "the functions of the brain are activated, imagination is lively, thoughts have a peculiar charm and, in some persons, symptoms of intoxication are present." Junod suggested that narcosis resulted from pressure causing increased blood flow and hence stimulating nerve centers. Walter Moxon (1836–1886), a prominent Victorian physician, hypothesized in 1881 that pressure forced blood to inaccessible parts of the body and the stagnant blood then resulted in emotional changes. The first report of anesthetic potency being related to lipid solubility was published by Hans H. Meyer in 1899, entitled Zur Theorie der Alkoholnarkose. Two years later a similar theory was published independently by Charles Ernest Overton. What became known as the Meyer-Overton hypothesis may be illustrated by a graph comparing narcotic potency with solubility in oil. In 1939, Albert R. Behnke and O. D. Yarborough demonstrated that gases other than nitrogen also could cause narcosis.
Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond 40 m (130 ft) 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. 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, 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 effect of carbon dioxide is a consistent diminution of mental and psychomotor function. 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 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. Signs and symptoms
Due to its perception-altering effects, the onset of narcosis may be hard to recognize.