A mathematical model for predicting cardiovascular responses at rest and during exercise in demanding environmental conditions

The present research describes the development and validation of a cardiovascular sub-model (CVR Model) for use in conjunction with advanced thermophysiological models, where usually only a total cardiac output is estimated. The CVR Model detailed herein estimates cardio-dynamic parameters (changes in cardiac output, stroke volume, heart rate), regional blood flow, and muscle oxygen extraction, in response to rest and physical workloads, across a range of ages and aerobic fitness levels, as well as during exposure to heat, dehydration, and altitude. The model development strategy was to first establish basic resting and exercise predictions for cardiodynamic parameters in an 'ideal' environment (cool, sea level, hydrated person). This basic model was then advanced for increasing levels of altitude, heat strain and dehydration, using meta-analysis and reaggregation of published data. Using the estimated altitude- and heat-induced changes in maximum oxygen extraction and maximum cardiac output, the decline in maximum oxygen consumption at high-altitude and in the heat was also modelled. A validation of predicted cardiovascular strain using heart rate was conducted using a dataset of 101 heterogeneous individuals (1371 data points) during rest and exercise in the heat and at altitude, demonstrating that the CVR model performs well (R² = 0.82-0.84) in predicting cardiovascular strain, particularly at a group mean level (R² = 0.97). The development of the CVR Model is aimed at providing the FPC Model and other complex thermophysiological models with improved estimations of cardiac strain and exercise tolerance, across a range of individuals during acute exposure to environmental stressors.