ABSTRACT
BACKGROUND: The recommended maximum water temperature for public hot tubs has been set at 40.0 degrees C, but no research has been published on human immersion in hot water at higher temperatures. HYPOTHESIS: We hypothesized that thermoregulatory and cardiovascular responses at two water temperatures would be proportional to the water:blood temperature gradients. METHODS: Six healthy men were immersed for 21 min in circulating hot water at 40.0 and 41.5 degrees C in separate trials in random order 1-3 wk apart. Measurements included heart rate, systolic BP, esophageal, rectal, and non-immersed skin temperatures, sweat rate, and perceived comfort. RESULTS: The rise in all body temperatures, sweat rate, and heart rate were significantly greater in the 41.5 vs. 40.0 degrees C water. Peak esophageal temperatures were 38.3 +/- 0.2 degrees C vs. 37.8 +/- 0.03 degrees C, peak sweat rates were 0.48 +/- 0.05 vs. 0.32 +/- 0.03 kg x m(-2) x h(-1), and peak heart rates were 123 +/- 7 vs. 108 +/- 5 bpm, respectively. Systolic BPs followed different patterns of response in each trial, whereas diastolic pressures were not different between trials. Comfort at each level of immersion was reduced during the 41.5 degrees C trial compared with the 40.0 degrees C in excess of that predicted by difference in esophageal temperature between the trials. CONCLUSIONS: These results suggest that risks of hyperthermia or adverse cardiovascular effects in hot tubs may not be greater in water above 40.0 degrees C unless perceptual judgment is impaired. Hypotension when standing to exit the tub occurred in both trials and may represent a potential hazard to hot tub use.
Subject(s)
Body Temperature Regulation/physiology , Cardiovascular System/physiopathology , Hot Temperature/adverse effects , Hydrotherapy/adverse effects , Immersion/physiopathology , Adult , Blood Pressure , Confusion/etiology , Fever/etiology , Heart Rate , Humans , Hypotension/etiology , Male , Skin Temperature , Sweating/physiology , Time FactorsABSTRACT
The goals of the study were to test the hypotheses that ethyl alcohol (ETOH) in low-to-moderate doses would alter thermo-regulation and/or disrupt the normal relationship between physiological and psychophysical indexes of heat stress during 40 degrees C water immersion and to characterize the cardiovascular response to the combined stimuli of heat, water immersion, and ETOH. Six healthy men underwent three trials of 21 min of immersion in water at 40.0 +/- 0.1 degrees C after consuming 0, 0.27, or 0.54 g ETOH/kg. Esophageal temperature (Tes) rose by approximately 1.0 degrees C during immersion for each trial. Per unit of Tes rise, changes during immersion in skin temperature, sweat rate, heart rate, systolic and diastolic blood pressure, and psychophysical assessments of comfort and overheating did not differ significantly by trial. Across trials, there was an apparent threshold for activation of thermoregulatory responses at an approximately 0.5 degrees C increase in Tes occurring after approximately 9 min of immersion. This threshold was identified psychophysically by increased ratings of overheating and decreased comfort. Above the threshold, there was an attenuation of the rate of increase of Tes. Cardiovascular stress was mild (rate-pressure product approximately 12,000) and not significantly increased by ETOH. Hypotension and tachycardia when subjects stood to exit the tub were observed. The data suggest that ETOH at the doses administered does not affect thermoregulatory, cardiovascular, or psychophysical indexes of heat stress during 40 degrees C water immersion.
