The model of human thermoregulatory system for positive heat loads

Body heat balance was calculated in men subjected to endogenous or exogenous heat load in order to test whether the human thermoregulatory system may be regarded as a servomechanism of heat exchange. Two series of experiments were carried out with male volunteers. In series I fifteen subjects performed 60 min physical exercise (at 50% V O2 max) at a constant ambient temperature of 25 degrees C. In series II sixteen subjects rested in a climatic chamber where the ambient temperature was increasing during 30 min from 22 to 42 degrees C and kept stable at this high level during subsequent 60 min. It was found, that in both series of experiments the sweating rate followed an exponential curve exhibiting an inertial course. The heat was stored in the body mainly at the beginning of experiments. It is concluded, that under the present experimental conditions, the heat loss from the body by sweat evaporation seems to be a regulated variable in the human thermoregulatory system. According to this conclusion the model of human thermoregulatory system acting as a servomechanism is proposed. In this model the "set-point" concept is unnecessary.