Seasonal effects of sleep deprivation on thermoregulatory responses in a hot environment.

Effects of sleep deprivation and season on thermoregulation during 60 min. of leg-bathing (water temperature of 42 degrees C, air temperature of 30 degrees C, and relative humidity of 70%) were studied in eight men who completed all 4 experiments for normal sleep and sleep deprivation in summer and winter. Rectal temperature (T(re)), skin temperature, total body sweating rate (M(sw-t)), local sweating rate on the back (M(sw-back)) and forearm (M(sw-forearm)), and skin blood flow on the back (SBF(back)) and forearm (SBF(forearm)) were measured. The changes in T(re) (DeltaT(re)) were smaller (P<0.05) for sleep deprivation than for normal sleep regardless of the season. This decrease in DeltaT(re) was significant only in summer (P<0.05). Mean skin temperature (T(mean of)(sk)) was higher (P<0.05) for sleep deprivation than for normal sleep regardless of the season. M(sw-t) was smaller (P<0.05) for sleep deprivation than for normal sleep regardless of season, although M(sw-back) and M(sw-forearm) were similar. SBF(back) and SBF(forearm) tended to be higher for sleep deprivation than normal sleep. The sensitivity of SBF to T(re) was higher (P<0.05) for sleep deprivation than for normal sleep. These data indicate that seasonal differences in thermoregulation were small because of morning time. Sleep deprivation increased dry heat loss and restrained T(re) rise, in spite of decreased sweating rate.