Objective: This 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.
Methods: In 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), muscles (vastus medialis and triceps brachii) under normal resting conditions (errors between 0.0 and 0.5 °C), and the rectum under different heat-stress conditions (errors between 0.1 and 0.3 °C), with experimental measurements from multiple studies.
Results: Our 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.
Conclusion: Our 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.
Keywords: Core body temperature; environmental heat stress; exertional heat stress; finite element model; heat illness.