Psychophysiologic changes in sleep during simulated 200-m heliox saturation dives

The standard polysomnogram and questionnaire were measured from 4 subjects during 2 simulated 200-m heliox saturation dives. These measurements were performed for 1 precompression night, bottom nights, 4 or 5 nights during decompression, and 1 postdecompression night. Although the subjects reported a marked decrease in quantity and quality of sleep at the bottom, only a slight degree of sleep disturbance caused by frequent awakenings was found in polysomnograms. Throughout the dive period, latency of each sleep stage, quantity of REM sleep, and the REM-NREM cycle showed no changes, whereas quantity of slow wave sleep remained at a low level. From these results it was inferred that basic sleep mechanisms were not affected under 200-m heliox environment. Unusual physiologic phenomena were observed during the dive period. Intermittent diffuse rhythmic theta activity was found in 1 subject at sleep stage REM during the bottom. Rhythmic contraction of facial muscles, which was similar to bruxism, increased, particularly at sleep stage 2 in all subjects during decompression.