Predicting heart rate response to various metabolic rates, environments, and clothing

A mathematical model that describes heart rate (HR) responses to different combinations of metabolic levels, climatic conditions, and clothing ensembles was developed. The database that served to construct the model consisted of 48 variations representing a wide range of environmental conditions, clothing ensembles, and metabolic rates. The model, which correlates highly with the observed values (r = 0.88, P < 0.0001), is based on physiological and environmental parameters: HR = 57.1 + 0.6HRi + [0.07M - 19.06 – 0.011(Emax - Ereq)] log t, where HRi is initial HR in beats per minute (at rest before the exposure), t is the time of exposure in minutes, M is the metabolic rate in watts, Ereq is the required sweat evaporation for thermal equilibrium in watts, and Emax is the maximal evaporative capacity of the environment in watts. The model's validity was tested by using two independent databases representing wide ranges of conditions; the correlation between measured and predicted values was found to be highly significant (r = 0.83, P < 0.001 and r = 0.77, P < 0.001, respectively). In summary, the present study suggests a valid predictive model for HR that overcomes some of the difficulties observed in other models.