Simulation of thermal cardiovascular strain using a thermophysiological model: abstract

Introduction Exercise in a warm environment is typically correlated with a higher heart rate (HR) than the same exercise in a cool environment. In literature this effect is explained by the increased cardiac output (CO) due to increased skin blood flow, complemented with reductions in stroke volume (SV) due to venous pooling and dehydration. Here we aimed to mechanistically model these processes to simulate thermal cardiovascular strain with a thermophysiological model. Methods The TNO thermophysiological model (Scope v3) was extended with a cardiovascular module to accommodate the dynamics in blood flow for muscle, organs and skin compartments (required CO); as well as the dynamics in SV. HR was then calculated as CO/SV. Test data were collected by measuring core temperature (TC) and heart rate in healthy young adult male participants (n=9) during 45min cycling (100W), in a warm environment (32°C, 50%rh), in shorts (0.4Clo) and battle dress uniform (bdu, 1Clo). The root mean squared residual (RMSR) was used to quantify the error of the simulation. Results During experiments average TC and HR increased (TCshorts 37.0°C to 37.8°C, TCbdu 37.2°C to 38.2°C, and HRshorts 114BPM to 137BPM, HRbdu 115BPM to 146BPM). TC was simulated within 0.10°C (RMSRshorts= 0.07°C,RMSRbdu=0.04°C). HR was simulated within 5BPM (RMSRshorts=4.1BPM,RMSRbdu=4.0BPM). There was a clear similarity in the shape of measured vs. simulated HR, and there was no underestimation. Conclusion Results give a proof of concept that thermal cardiovascular strain can be simulated accurately with a thermophysiological model as a basis. Validation on independent datasets is required to test the general applicability of the cardiovascular module.