An improved thermo-cardiovascular model for individual thermophysiological prediction in non-uniform indoor thermal environments

Many individuals face health risks owing to altered thermophysiological responses in non-uniform indoor thermal environments (e.g., bathing), with cardiovascular disorders being a significant concern, particularly among older adults. Experimental studies alone are insufficient to fully comprehend individual physiological responses and develop preventive strategies due to ethical and practical limitations. Therefore, it is crucial to model the thermophysiological responses at the individual level. This study proposed an improved thermo-cardiovascular regulation model (TCRM) by modifying the calculation of blood resistance and incorporating individual height, weight, and age-specific physiological parameters, including the basal metabolic rate, sweat threshold temperature, vascular compliance, blood distribution, and capillary resistance. The model predicts skin and core temperature, blood pressure, and regional blood flow in three participants (25, 52, 71 years) during non-uniform bathing (half-body immersion: lower body in hot water to chest level, upper body in room air). Evaluation using root mean square error (RMSE) and the coefficient of determination (R²) showed that the model accurately reproduced individual thermophysiological responses. Despite the limited sample, this proof-of-concept study demonstrates that the age-adapted TCRM can capture individual variations in skin temperature, core temperature, blood pressure, and blood flow under non-uniform thermal conditions. This work provides a methodological foundation for larger, prospective validations.