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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, [2] 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.
Narcosis can produce tunnel vision, making it difficult to read multiple gauges. Nitrogen narcosis is a change in consciousness, neuromuscular function, and behavior brought on by breathing compressed inert gasses, most commonly nitrogen. It has also been called depth intoxication, “narks,” and rapture of the deep.
Helium both enters and leaves the body faster than nitrogen, so different decompression schedules are required, but, since helium does not cause narcosis, it is preferred over nitrogen in gas mixtures for deep diving. [59] There is some debate as to the decompression requirements for helium during short-duration dives.
Nitrogen narcosis is also called “L’ivresse des grandes profondeurs” or "rapture of the deep". Nitrogen constitutes 78% of dry air, but at surface pressures it has no sedating effect. At greater depths, however, nitrogen affects the brain in the same way as nitrous oxide (also known as laughing gas ) and other anaesthetic gases.
DCI can be caused by two different mechanisms, which result in overlapping sets of symptoms. The two mechanisms are: Decompression sickness (DCS), which results from metabolically inert gas dissolved in body tissue under pressure emerging out of solution and forming bubbles during decompression.
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. [5] A lower proportion of oxygen reduces the risk of oxygen toxicity on deep dives. The lower density of helium reduces breathing resistance at depth.
Although carbon dioxide (CO 2) is known to be more narcotic than nitrogen – a rise in end-tidal alveolar partial pressure of CO 2 of 10 millimetres of mercury (13 mbar) caused an impairment of both mental and psychomotor functions of approximately 10% – [5] [2] the effects of carbon dioxide retention are not considered in these calculations, as the concentration of CO 2 in the supplied ...
Narcosis while deep diving is prevented by breathing a gas mixture containing helium. Helium is stored in brown cylinders. The most straightforward way to avoid nitrogen narcosis is for a diver to limit the depth of dives. Since narcosis becomes more severe as depth increases, a diver keeping to shallower depths can avoid serious narcosis.