Finite Element Model of Human Thermoregulation in Cold Conditions

Abstract

The human body can only function properly within a narrow range of temperatures. Therefore, the regulation of body temperature is a critical part of survival. Thermal homeostasis is maintained through complex feedback loops, with the body reacting to local temperature changes. The critical components of this feedback loop are linked to the skin temperature and the hypothalamus temperature. the skin is responsible for heat sensing, while the hypothalamus is the body’s temperature control center. In this study the effect of thermoregulation on the temperature of multiple domains throughout the body was considered, and an attempt to create a 3-dimensional model that accurately displays its effect on body temperature was attempted. To investigate the effect that thermoregulation has on maintaining temperature and to investigate the accurate temperature profile of the human body, COMSOL, a finite element software capable of running physics simulations, was utilized. There had been previous research on the topic that used only a few hundred nodes or used lumped parameters to simulate thermal regulation. Our model’s geometry was 3-dimensional and inspired by the dimensions used in a previous model by Dr. Dusan Fiala [1]. To implement thermoregulatory effects, empirical formulas were found in previous literature for shivering, vasodilation and vasoconstriction among others. All empirical formulas were temperature sensitive and were functions of the skin temperature and/or the hypothalamus temperature. These effectors change the local heat generation terms and the local blood perfusion terms, both crucial components of the heat equation in biological systems. An initial simulation of the body temperature was run at cool environment with some air flow. The results showed a sharp decline in average skin and fat temperatures initially due to their proximity to the surface, while the average brain temperatures declined gradually and then flattened off within the first two hours. Simulations excluding different components of thermoregulation were also ran to portray the importance of thermoregulation in the body. The simulations without thermoregulatory components resulted in much lower brain temperatures, as expected . Furthermore, the magnitude of different effectors were measured, allowing for analysis on the importance of different ways body’s thermoregulate. To validate the model, experimental data was compared to our simulated result. Experimental data regarding skin temperature over time, and shivering magnitude over time matched the overall trend of our data. Similarly, research on what external temperatures induce shivering were in line with the simulated results. This model provides insight into the distribution of temperature across the human body and will provide the basis of a comprehensive human model applicable to a range of topics, such as clothing insulation and frostbite analysis. By incorporating empirical equations that are functions of temperature and having a 3D model that is heavily discretized, the model can accurately portray the body’s temperature profile in cold climates.