A 3-D virtual human thermoregulatory model to predict whole-body and organ-specific heat-stress responses

Ginu Unnikrishnan,Douglas J Casa,Gabrielle E W Giersch,Luke N Belval,Rajeev Hatwar,Jaques Reifman,Srinivas Laxminarayan,Josh B Kazman,Samantha Hornby,Tushar Gulati

doi:10.1007/s00421-021-04698-1

Abstract

ObjectiveThis study aimed at assessing the risks associated with human exposure to heat-stress conditions by predicting organ- and tissue-level heat-stress responses under different exertional activities, environmental conditions, and clothing.MethodsIn this study, we developed an anatomically detailed three-dimensional thermoregulatory finite element model of a 50th percentile U.S. male, to predict the spatiotemporal temperature distribution throughout the body. The model accounts for the major heat transfer and thermoregulatory mechanisms, and circadian-rhythm effects. We validated our model by comparing its temperature predictions of various organs (brain, liver, stomach, bladder, and esophagus), and muscles (vastus medialis and triceps brachii) under normal resting conditions (errors between 0.0 and 0.5 °C), and of rectum under different heat-stress conditions (errors between 0.1 and 0.3 °C), with experimental measurements from multiple studies.ResultsOur simulations showed that the rise in the rectal temperature was primarily driven by the activity level (~ 94%) and, to a much lesser extent, environmental conditions or clothing considered in our study. The peak temperature in the heart, liver, and kidney were consistently higher than in the rectum (by ~ 0.6 °C), and the entire heart and liver recorded higher temperatures than in the rectum, indicating that these organs may be more susceptible to heat injury.ConclusionOur model can help assess the impact of exertional and environmental heat stressors at the organ level and, in the future, evaluate the efficacy of different whole-body or localized cooling strategies in preserving organ integrity.

Highlights

Heat-related illnesses induced by strenuous physical activity, exposure to adverse environmental conditions, or their combination necessarily involve an increase in core body temperature (Epstein and Roberts 2011; Bouchama and Knochel 2002; Epstein et al 2012)
To represent the macroscopic energy balance within the body, we used the Pennes bioheat transfer equation, wherein we modeled heat generated in the body due to basal metabolism and physical activity, heat conduction, and heat convection through blood perfusion
We simulated steady state for a boundary condition corresponding to the thermoneutral state (i.e., 30 °C and 40% relative humidity with T-shirt/shorts and without any physical activity) and monitored core body temperature at the rectum

Summary

Introduction

Heat-related illnesses induced by strenuous physical activity, exposure to adverse environmental conditions, or their combination necessarily involve an increase in core body temperature (Epstein and Roberts 2011; Bouchama and Knochel 2002; Epstein et al 2012). Because it is not feasible to measure organ temperature in humans while performing strenuous physical activity, one way to address this challenge is to use computational models to characterize the spatiotemporal distribution of temperatures throughout the entire body resulting from exertional and environmental heat stressors and use this information to infer potential organ-specific injury. While the single- and multiple-segment models have been shown to reasonably predict core body temperature as well as skin temperature under different heat-stress conditions (Fiala et al 1998, 2001), they inherently lack the spatial resolution to predict temperature responses at the organ and tissue levels (Nelson et al 2009), which limits their applicability

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Conclusion