Effect of continuous heat exposure on sleep during partial sleep deprivation

Abstract

This study examined the effects of continuous heat exposure on sleep structure during a partial sleep-deprivation regime. The experimental protocol was divided into three periods. After a baseline period (5 days and nights at 20°C), the sleep of the subjects was restricted 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°C for six of the 12 subjects and 35°C for the others. Sleep, esophageal and mean skin temperatures were continuously recorded. At 20°C, the expected effect of sleep debt 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-sleep nights, whereas esophageal temperature significantly decreased over the successive days. When heat was added, esophageal temperature decrease was weakened, and the significant increase in stage 4 duration seen at 20°C was not found. The findings suggest that the heat load imposed in our experimental condition has a suppressive effect on sleep stage 4 increase, which is induced by sleep restriction. The hypothesis that an increase in this sleep stage serves as a mechanism for energy conservation should be also considered.