[Sleep as a restorative process under extreme exposure conditions].

In 40 aquanauts, a prolonged stay under increased pressure (11 to 46 kgs/cm2) of the oxygen-helium-nitrogen mixture did not affect the average duration of sleep. Slow-wave sleep, mostly its 3 rd and 4 th stages, and paradoxical sleep were significantly decreased whereas the light sleep/profound sleep ratio increased. The cyclic structure of sleep became altered. The longer the exposure to high pressure led to an augmentation of the slow-wave sleep and REM-phase, but the normal cycles terminating with a REM-phase could not be formed during the experiment.