title: Effect of short-term exercise-heat acclimation on ventilatory and cerebral blood flow responses to passive heating at rest in humans.
abstract: Hyperthermia induces hyperventilation and cerebral hypoperfusion in resting humans. We tested the hypothesis that short-term exercise-heat acclimation would alleviate those effects. Twenty healthy male subjects were divided into two groups that performed exercise training in the heat (TR-HEAT, n = 10) or cold (TR-COLD, n = 10). Before and after the training, the subjects in both groups participated in passive-heat tests at rest. Training was performed at 37°C (TR-HEAT) or 10°C (TR-COLD) and entailed four 20-min bouts of cycling at 50% peak oxygen uptake separated by 10-min recoveries daily for 6 consecutive days. After TR-HEAT, esophageal temperature was lowered when measured before and during passive heating, as was the esophageal temperature threshold for cutaneous active vasodilation, whereas plasma volume was increased (all P < 0.05). These traditional indices of successful heat acclimation were not all induced by TR-COLD (all P > 0.05). TR-HEAT had no significant effect on passive heating-induced increases in minute ventilation, even when evaluated as the esophageal temperature threshold for increases in minute ventilation and the slope relating minute ventilation to esophageal temperature (all P > 0.05). By contrast, TR-HEAT attenuated the passive heating-induced reduction in the cerebral vascular conductance index (middle cerebral artery mean blood velocity/mean arterial pressure) (all P < 0.05). TR-COLD did not attenuate the increase in minute ventilation or the decrease in the cerebral vascular conductance index observed during passive heating (all P > 0.05). These data suggest that in resting heated humans, short-term heat acclimation achieved through moderate-intensity exercise training (i.e., 50% peak oxygen uptake) in the heat does not influence hyperthermia-induced hyperventilation, but it does potentially attenuate cerebral hypoperfusion.
authors.affiliation: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan; Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada; and.
authors.forename: Naoto
authors.initials: N
authors.lastname: Fujii
authors.affiliation: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan;
authors.forename: Bun
authors.initials: B
authors.lastname: Tsuji
authors.affiliation: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan;
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Honda
authors.affiliation: Faculty of Human Development, Kobe University, Kobe, Japan.
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan; nisiyasu@taiiku.tsukuba.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishiyasu
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D062186:Arterial Pressure / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003080:Cold Temperature; D015444:Exercise / Q000502:physiology*; D005334:Fever / Q000503:physiopathology; D006361:Heating / Q000379:methods; D006706:Homeostasis / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology; D008297:Male; D010953:Plasma Volume / Q000502:physiology; D012146:Rest / Q000502:physiology*; D013546:Sweating / Q000502:physiology
keywords: cerebral perfusion; control of breathing; exercise training; orthostatic tolerance; respiratory alkalosis