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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.
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.
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.
When inhaled at high partial pressures (more than about 4 bar, encountered at depths below about 30 metres in scuba diving), nitrogen begins to act as an anaesthetic agent, causing nitrogen narcosis. [5] [6] However, the minimum alveolar concentration (MAC) for nitrogen is not achieved until pressures of about 20 to 30 atm (bar) are attained. [7]
DAN publishes research results on a wide range of matters relating to diving safety and medicine and diving accident analysis, including annual reports on decompression illness and diving fatalities. Most are freely available on the internet, many of these were at the now defunct Rubicon Research Repository. [needs update]
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. [1] A lower proportion of nitrogen is required to reduce nitrogen narcosis and other physiological effects of the
Greater depth can expose a diver to factors such as increased air consumption, impaired judgment caused by nitrogen narcosis, colder water, reduced thermal insulation of a compressed wetsuit, reduced visibility and lighting, slower response of buoyancy compensator inflation, increased work of breathing, greater heat loss when using helium ...