Effects of breathing nitrogen under increased pressure. In divers breathing compressed air, nitrogen saturates the nervous system, causing an intoxicating light-headed, numb feeling, then slowed reasoning and dexterity, and then emotional instability and irrationality. Severe cases progress to convulsions and blackout. Susceptibility varies, and severity increases with depth, but there are no aftereffects. Physical function remains normal, and divers may be unaware of the growing irrationality that can cause them to rise too fast (see decompression sickness) or let their air supply run out. Helium, which dissolves less easily in body tissues, is substituted for nitrogen for deep dives.
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