Thermoregulatory and cardiovascular responses to up-step change transient thermal environments: A risk factor in individuals with prosthetic heart valves

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Exposure to step-change thermal environments can trigger the human body's thermoregulatory processes. The reactivation of thermoregulatory mechanisms is usually accompanied by the excitation of cardiovascular responses. This paper presents a combined thermoregulatory-cardiovascular model for predicting the effect of transient thermal environments on heart rate and cardiovascular responses. The proposed model was validated against multiple sets of experimental data reported in the literature. The validation results showed that the proposed model, which considers the thermoregulatory effects, could predict heart rate more accurately compared to the Givoni and Goldman practical model. The impacts of different up-step temperature changes on cardiovascular responses were investigated using the proposed model. The results showed that exposure to a relatively small (10°C), medium (20°C), and large (30°C) up-step temperature changes increased the heart rate by about 7%, 20%, and 35%, respectively. It was also found that ambient relative humidity did not have remarkable effects on cardiovascular responses. The results of our analysis performed in the temperature range of 20°C to 50°C showed that the heart rate could reflect the reactivation of the body's thermoregulatory mechanisms. The findings indicated that in people with artificial heart valves, sudden exposure to temperature step-changes of 10°C to 30°C could increase the heart valve pressure drop by about 14%–85%, greatly increasing the risk of blood damage. Furthermore, it is concluded that the proposed model can pave the path for utilizing integrated wearable devices for predicting individualized thermal comfort and managing cardiovascular health risks associated with ambient heat stresses.