Regulation of local sweating in sleep-deprived exercising humans

Summary Thermoregulatory sweating [total body (m_sw,b), chest (m_sw,c) and thigh (m_sw,t) sweating], body temperatures [oesophageal (T_oes) and mean skin temperature (T_sk)] and heart rate were investigated in five sleep-deprived subjects (kept awake for 27 h) while exercising on a cycle (45 min at approximately 50% maximal oxygen consumption) in moderate heat (T_air andT_wall at 35° C. Them_sw,c andm_sw,t were measured under local thermal clamp (T_sk,1), set at 35.5° C. After sleep deprivation, neither the levels of body temperatures (T_oes,T_sk) nor the levels ofm_{sw, b},m_{sw, c} orm_{sw, t} differed from control at rest or during exercise steady state. During the transient phase of exercise (whenT_sk andT_sk,1 were unvarying), them_{sw, c} andm_{sw, t} changes were positively correlated with those ofT_oes. The slopes of them_{sw, c} versusT_oes, orm_{sw, t} versusT_oes relationships remained unchanged between control and sleep-loss experiments. Thus the slopes of the local sweating versusT_oes, relationships (m_{sw, c} andm_{sw, t} sweating data pooled which reached 1.05 (SEM 0.14) mg·cm^–2·min^–1°C^–1 and 1.14 (SEM 0.18) mg·cm^–2·min^–1·°C^–1 before and after sleep deprivation) respectively did not differ. However, in our experiment, sleep deprivation significantly increased theT_oes threshold for the onset of bothm_{sw, c} andm_{sw, t} (+0.3° C,P<0.001). From our investigations it would seem that the delayed core temperature for sweating onset in sleep-deprived humans, while exercising moderately in the heat, is likely to have been due to alterations occurring at the central level.