Predicting survival time for cold exposure by thermoregulation modeling: Fid-Bau Portal

Predicting survival time for cold exposure by thermoregulation modeling

Zhao, Jinping / Wang, Yan / Ou, Dengsong / Wang, Hanqing / Li, Yuguo / Deng, Qihong

Abstract Background Extreme temperatures are becoming increasingly common due to global warming. Extreme cold and heat events lead to an increase in mortality rates. More deaths occur in cold weather as a result of hypothermia. However, the change progress of body core temperature and the survival time during cold exposure has yet to be extensively studied. Objectives To establish a mathematical thermoregulatory model for prolonged cold air exposure and to propose a method for predicting survival time under sedentary conditions. Methods We extended the classical multi-segment multi-node human thermoregulatory model by considering the effects of thermoregulatory fatigue on shivering and vasoconstriction based on the variable setpoint theory. The core threshold temperatures and the sensitivity of the responses decreased with the degree of fatigue (fa). The model was then used to systematically examine the effects of environmental parameters on the time course of body core temperature in the development of fatal hypothermia. A new wind chill index was constructed based on the simulated data of our thermoregulatory model to estimate the survival time. Results Our extended thermoregulatory model predicted that during prolonged cold air exposures, body core temperature would decrease in three distinct stages: an initial decrease due to uncompensated cooling load, an equilibrium plateau due to shivering, and a final rapid drop due to thermoregulatory fatigue. Fatal hypothermia occurred at the third stage due to impaired shivering and vasoconstriction caused by fatigue. Lower air temperature and higher air speed can accelerate the occurrence of hypothermia. We proposed a predictive equation for survival time, i.e., the maximum endurance time before fatal hypothermia occurs, which is an exponential function of the wind chill index, and the newly defined wind chill index considers the contribution from both air temperature and air speed. Conclusions We suggest a new thermoregulatory model to predict the fatal hypothermia due to thermoregulatory fatigue during cold air exposure. We proposed a survival time chart based on a new wind chill index, which can be used to alert the early risk of fatal hypothermia during extreme cold events.

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Highlights • Thermoregulatory fatigue is a dominant factor leading to hypothermia during cold exposure. • Thermoregulatory fatigue leads to attenuated shivering and vasoconstriction during cold exposure. • $T_{core}$ course consists of three stages: a slow decrease, an equilibrium plateau, and a rapid drop. • Survival time is an exponential function of the new wind chill index defined by $T_{a}$ and $V_{a}$ . • Thermoregulation modeling can be used to predict and early recognize the risk of hypothermia.