EEG and sleep disturbances during dives at 450 msw in helium-nitrogen-oxygen mixture

To study the effects of nitrogen addition to the breathing mixture on sleep disturbances at pressure, two dives were performed in which helium-nitrogen-oxygen mixture was used up to 450 m sea water (msw). In total, sleep of 12 professional divers was analyzed (i.e., 184 night records). Sleep was disrupted by compression and by stay at 450 msw: we observed an increase in awake periods and in sleep stages I and II and a decrease in stages III and IV and in rapid-eye-movement sleep periods. These changes, which were more intense at the beginning of the stay, began to decrease from the seventh day of the stay, but the return to control values was recorded only during the decompression at depths below 200 msw. These changes were equivalent to those recorded in other experiments with helium-oxygen mixture in the same range of depths and were independent of the intensity of changes recorded in electroencephalographic activities in awake subjects.