Metabolism and thermoregulation during stages of sleep in humans exposed to heat and cold.

Electrophysiological stages of sleep, oxygen consumption (VO2), and skin (Tsk) and rectal (Tre) temperatures were recorded from six virtually naked male subjects exposed to ambient temperatures (Ta) of 21, 24, 29, 34, and 37 degrees C. VO2 increased during sleep as a whole as Ta departed from thermoneutrality (29 degrees C) and was significantly greater during rapid-eye-movement (REM) sleep than during adjacent nonrapid-eye-movement (NREM) periods at low and high Ta but not at 29 degrees C. Tsk showed small but significant increases during REM sleep at 29, 34, and 37 degrees C, but Tre did not change during REM sleep at any Ta. Shivering was present during wakefulness at 21 and 24 degrees C but occurred only occasionally during stages 1 and 2 sleep at 21 degrees C. The increases in VO2 and the absence of marked changes in vasomotor tone during REM sleep in the cold were unexpected and possibly indicate that REM sleep is not as thermally disruptive in humans as in other mammals.