Abstract
Humans have higher ventilation when they are hyperthermic but it is not known whether core temperature thresholds for ventilation exist, nor has a physiological rationale been presented for this response. To examine this question, ventilation was studied in relation to core temperatures in humans rendered hyperthermic in a warm bath. Seven subjects [mean (SE), 23.3 (1.4) years] wearing only shorts and a thick felt hat with ear flaps were immersed to the neck in a bath at 41 (0.5)°C for 25 min. Tympanic (T ty), esophageal (T es), thigh skin and forehead skin temperatures, heart rate, inspired minute ventilation (V I at body temperature and pressure, saturated), ventilation frequency and oxygen consumption (VO2 at standard temperature and pressure, dry) were recorded at 30-s intervals. At immersion V I briefly increased to 18.6 (3.0)l·min−1 returned to about the pre-immersion value,, and significantly increased to 19.3 (3.0) l·min−1 by the end of immersion. VO2 increased significantly from the pre-immersion value of 0.27 l·min−1 to 0.67 l·min−1 by the first 0.5 min of immersion, but then returned to its pre-immersion value. T ty increased to 38.7 (0.2)°C and T es increased to 39.0 (0.2)°C by the end of immersion. Core temperature thresholds for increases in V I were evident at 38.1°C when expressed against T ty and at 38.5°C when expressed against T es. The results indicated that during body warming core temperature thresholds for V I are reached and subsequently a hyperpnea was evident, despite VO2 remaining at a resting value. This hyperpnea is seen as a thermoregulatory response likely to participate in selective brain cooling.
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Cabanac, M., White, M.D. Core temperature thresholds for hyperpnea during passive hyperthermia in humans. Europ. J. Appl. Physiol. 71, 71–76 (1995). https://doi.org/10.1007/BF00511235
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DOI: https://doi.org/10.1007/BF00511235