Subjective and behavioural responses to nitrogen narcosis and alcohol.

RATIONALE There is a widespread assumption that nitrogen narcosis is comparable to alcohol intoxication, a similarity that may extend to patterns of tolerance. It has been suggested this indicates evidence of a shared biological mechanism but there is a paucity of experimental data to support these claims. OBJECTIVE The current study aimed to test this assumption by comparing subjective (ratings) and behavioural (Digit Letter Substitution Test) responses to nitrogen narcosis and alcohol. METHODS Experiment 1 compared responses to narcosis in 39 participants posited to differ in tolerance based on prior exposure to alcohol (heavy/light drinkers) and narcosis (novice/experienced divers). Experiment 2 compared responses to narcosis and after a 0.5 g/kg dose of alcohol in 23 participants. In both experiments narcosis was measured at depths between 40 and 45m in the ocean off Port Vila, Vanuatu. RESULTS Experiment 1 measured a significant decrement in the behavioural measure underwater, compared to baseline but failed to find any differential responding to narcosis between drinker or diving experience groups. In contrast, Experiment 2 found positive correlations between alcohol and narcosis on both subjective and behavioural measures, indicating those affected to a greater degree by alcohol were also affected to a greater degree by narcosis. CONCLUSIONS These results support the contention of a relationship between nitrogen narcosis and alcohol, although the role of diving and drinking history, if any, remains obscure.