Subjective and behavioral effects associated with repeated exposure to narcosis

Below 30 m, nitrogen narcosis can severely degrade the performance of air breathing divers. Within the diving community it is generally thought that this effect can be reduced by repeating deep air dives on successive days but laboratory studies have found no strong evidence to support the notion of adaptation to narcosis. One possible explanation for this discrepancy is that one's subjective impression or perception of narcosis may decrease during repeated exposure to hyperbaric air without parallel improvement on task performance. To examine this possibility, symptoms and performance were examined over the course of 5 days of repeated exposure to 30% nitrous oxide at 1 ATA. While the results revealed no clear cut changes in global perceptions of narcosis across days, several symptoms from an adjective checklist showed unequivocal signs of adaptation. With respect to performance effects, reaction time yielded no indications of improvement over days relative to the control. These findings suggest that subjective adaptation can occur without parallel performance improvement, an effect which could compromise safety and which may be of concern in other operational settings that involve repeated exposure to stimulus conditions which impact on performance and symptoms.