Heatstroke at home: Prediction by thermoregulation modeling

Background: As global warming continues, the incidence of heatstroke due to exposure to high temperature will become more prevalent. Although most heatstroke deaths occur at home, the effect of home environment on the development of heatstroke has not yet been addressed. Objectives: To investigate the influences of home environmental parameters on the development of heatstroke using thermoregulation modeling. Methods: A classical multi-segment multi-node human thermoregulatory model was extended to consider the role of dehydration in the sweating and cutaneous vasodilation during exposure to heat stress. The model was then used to systematically examine the effects of indoor critical environmental parameters on the time course of body core temperature (T-core) in the development of heatstroke, and to estimate the survival time (tau(s)). Results: Our extended thermoregulatory model predicted that T-core course during heat stress consists of three stages: an initial linear increase due to uncompensated heat load, an equilibrium plateau due to sweating, and a final rapid progression due to dehydration. Heatstroke occurred either early at the first stage due to the lack of thermoregulation in hot and humid environment or late at the third stage due to thermoregulatory breakdown caused by dehydration in warm and dry environment. Increasing air velocity delayed occurrence time of heatstroke in warm and dry environment but advanced the occurrence time in hot and humid environment. We obtained the survival time tau(s) = exp(50 - ISI) where ISI = 44.2 + 0.02T(a) + 0.209RH - 6.55RH/T-a is the indoor stress index, indicating that the time that heatstroke occurs was exponentially increased with the indoor air temperature (Ta) and relative humidity (RH). Conclusions: We suggested a new thermoregulation model by considering the role of dehydration in the development of body core temperature during heat stress, which can be used to predict heatstroke at home. Easy-to-use indoor stress index and survival time table were obtained to early recognize and alert the risk of heat-stroke.