EFFECT OF CONTINUOUS HEAT EXPOSURE ON SLEEP DURING PARTIAL SLEEP-DEPRIVATION

This study examined the effects of continuous heat exposure on sleep s tructure during a partial sleep-deprivation regime. The experimental p rotocol was divided into three periods. After a baseline period (5 day s and nights at 20-degrees-C), the sleep of the subjects was restricte d to the second half of the night (3 a.m.-7 a.m.) for four consecutive nights. The restricted-sleep period was followed by two recovery days and nights. During the deprivation and recovery periods, the ambient temperature was 20-degrees-C for six of the 12 subjects and 35-degrees -C for the others. Sleep, esophageal and mean skin temperatures were c ontinuously recorded. At 20-degrees-C, the expected effect of sleep de bt was apparent. There were significant reductions in time spent awake and in latencies for sleep and stage 4 sleep. The duration of stage 4 sleep significantly increased during the four successive restricted-s leep nights, whereas esophageal temperature significantly decreased ov er the successive days. When heat was added, esophageal temperature de crease was weakened, and the significant increase in stage 4 duration seen at 20-degrees-C was not found. The findings suggest that the heat load imposed in our experimental condition has a suppressive effect o n sleep stage 4 increase, which is induced by sleep restriction. The h ypothesis that an increase in this sleep stage serves as a mechanism f or energy conservation should be also considered.