Adaptive Changes in the Indicators of Systemic Hemodynamics and Energy Consumption by Young Men during Passive Hyperthermia Procedures

— Adaptive shifts in systemic hemodynamic parameters and energy consumption were evaluated in 15 healthy young men in response to a single procedure of passive hyperthermia (PH) and during a course of ten such procedures. PH procedures with a duration of 40 min were performed in an infrared body heating capsule at 65–80°C, with the head remaining outside the capsule. Heart rate, blood pressure, and SрО 2 were analyzed. Oxygen and energy consumption were measured by indirect calorimetry. The sweating rate and the physiological strain index (PSI) were calculated. It was found that PH procedures were accompanied by an increase in energy consumption (in comparison with placebo procedures), but without a pronounced stress response of systemic hemodynamics. PSI values during PH corresponded to moderate heat stress. During the course, adaptive shifts occurred in the form of a decrease in energy consumption and an increase in the sweating rate. In the tenth procedure the relationship between the degree of increase in body temperature and the level of energy consumption was revealed.