Sleep organization in man during long stays at 30 and 40 bar in a helium-oxygen mixture

Sleep organization was studied during 5 dives with long holds (from 6 to 15 days) at 30 and 40 bar in a helium-oxygen mixture. In total, 16 professional divers participated in these saturation dives; 337 nights were analyzed. Sleep was disrupted by compression and the stay at pressure, but the disturbances were greater at 40 bar than at 30 bar. There was an increase of awake periods, stages I and II, a decrease of stages III and IV, and instability of rapid eye movement periods. These changes were more intense at the beginning of the stay; some improvements could be found between Days 4 and 6 of the stay but the return to control values was recorded only during the decompression after 20 bar. The disturbances of sleep seem to be related to compression speed and to the pressure itself and appear as another symptom of the high pressure nervous syndrome.