Dry-sauna is a strong thermal stimulus and is commonly used all over the world. The aim of this experiment was to comprehensively analyse cardiovascular and autonomic changes that result from an increase in core body temperature during sauna bath. The study included 9 healthy men with mean age 26.7 ± 3.0 years and comparable anthropomorphical characteristics. Each subject was exposed to one 15-minute session of dry-sauna treatment at 100°C and 30–40% humidity. The autonomic and baseline cardiovascular (i.e., hemodynamic and contractility) parameters were measured noninvasively with Task Force Monitor. Cardiovascular autonomic functions were assessed using baroreceptor reflex sensitivity (BRS) and spectral analysis of heart rate (HRV) and blood pressure (BPV) variability. Measurements were performed four times, at the following stages “before sauna,” “after sauna,” “sauna + 3？h,” and “sauna + 6？h.” The first recording constituted a baseline for the subsequent three measurements. The changes in core body temperature were determined with the Vital Sense telemetric measurement system. Results show that exposure to the extreme external environmental conditions of dry-sauna does not compromise homeostasis in healthy persons. The hemodynamic changes induced by heating are efficiently compensated by the cardiovascular system and do not exert negative effects upon its short-term regulatory potential. 1. Introduction Sauna constitutes one of the most popular and most extensively studied forms of whole-body thermal treatment. The idea of sauna originated in Scandinavian countries over a century ago and quickly gained popularity and it is now widely used worldwide [1–3]. The conditions of a sauna are determined by a combination of efficiency of thermoregulatory response, age, gender, and the cardiorespiratory performance of an individual [4, 5], together with the tradition of a given country. While high temperatures (90–100°C) and low humidity (10–15%) are typically used in Germany, Turkish sauna baths are completely different (70–80°C, 40%). In turn, infrared (IR) and far-infrared (FIR) saunas, with 45–60°C temperatures, are more popular in Canada [3, 6]. Recently, this latter form of dry sauna has gained popularity, described as a form of biological renewal because of a cardiovascular strain associated with the treatment [1]. The term “sauna,” used in medical literature, is derived from a traditional Finnish steam bath in a room heated by an electric stove. Overheating of the body takes place in a wooden room with temperatures approaching 70–100°C and low, 10–20%
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