Coombs Geoff B, Cramer Matthew N, Ravanelli Nicholas, Imbeault Pascal, Jay Ollie
School of Human Kinetics, Faculty of Health Sciences, University of Ottawa, ON, Canada.
Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia (Okanagan), Kelowna, BC, Canada.
Exp Physiol. 2021 Jan;106(1):359-369. doi: 10.1113/EP088466. Epub 2020 May 5.
What is the central question of this study? Hypoxia reportedly does not impair thermoregulation during exercise in compensable heat stress conditions: does it have an impact on maximal heat dissipation and therefore the critical environmental limit for the physiological compensability of core temperature? What is the main finding and its importance? Although skin blood flow was higher in hypoxia, no differences in sweat rates or the critical environmental limit for the physiological compensability of core temperature - an indicator of maximal heat loss - were found compared to exercise in normoxia, indicating no influence of normobaric hypoxia on thermoregulatory capacity in warm conditions.
Altered control of skin blood flow (SkBF) in hypoxia does not impair thermoregulation during exercise in compensable conditions, but its impact on maximal heat dissipation is unknown. This study therefore sought to determine whether maximum heat loss is altered by hypoxia during exercise in warm conditions. On separate days, eight males exercised for 90 min at a fixed heat production of ∼500 W in normoxia (NORM) or normobaric hypoxia (HYP, = 0.13) in a 34°C environment. Ambient vapour pressure was maintained at 2.13 kPa for 45 min, after which it was raised 0.11 kPa every 7.5 min. The critical ambient vapour pressure at which oesophageal temperature inflected upward (P ) indicated that maximum heat dissipation had been reached. Neither local sweat rates on the upper arm, back and forehead (average NORM: 1.46 (0.15) vs. HYP: 1.41 (0.16) mg cm min ; P = 0.59) nor whole-body sweat losses (NORM: 1029 (137) g vs. HYP: 1025 (150) g; P = 0.95) were different between trials. Laser-Doppler flux values (LDF; arbitrary units), an index of SkBF, were not different between NORM and HYP on the forearm (P = 0.23) or back (P = 0.73); however, when normalized as a percentage of maximum, LDF values tended to be higher in HYP compared to NORM at the forearm (condition effect, P = 0.05) but not back (P = 0.19). Despite potentially greater SkBF in hypoxia, there was no difference in P between conditions (NORM: 3.67 (0.35) kPa; HYP: 3.46 (0.39) kPa; P = 0.22). These findings suggest that hypoxia does not independently alter thermoregulatory capacity during exercise in warm conditions.
本研究的核心问题是什么？据报道，在可代偿热应激条件下运动时，低氧不会损害体温调节：它是否会对最大散热产生影响，进而影响核心温度生理可代偿性的临界环境极限？主要发现及其重要性是什么？尽管低氧状态下皮肤血流量较高，但与常氧运动相比，汗液分泌速率或核心温度生理可代偿性的临界环境极限（最大热量散失的指标）并无差异，这表明常压低氧对温暖环境下的体温调节能力没有影响。
低氧状态下皮肤血流量（SkBF）控制的改变在可代偿条件下运动时不会损害体温调节，但其对最大散热的影响尚不清楚。因此，本研究旨在确定在温暖环境下运动时，低氧是否会改变最大热量散失。在不同日期，8名男性在34°C环境中，以约500W的固定产热在常氧（NORM）或常压低氧（HYP， = 0.13）条件下运动90分钟。环境蒸汽压在45分钟内维持在2.13kPa，之后每7.5分钟升高0.11kPa。食管温度向上转折时的临界环境蒸汽压（P ）表明已达到最大散热。上臂、背部和前额的局部汗液分泌速率（平均NORM：1.46（0.15）与HYP：1.41（0.16）mg cm min ；P = 0.59）和全身汗液流失量（NORM：1029（137）g与HYP：1025（150）g；P = 0.95）在各试验之间均无差异。作为SkBF指标的激光多普勒血流值（LDF；任意单位）在前臂（P = 0.23）或背部（P = 0.73）的NORM和HYP之间没有差异；然而，当作为最大值的百分比进行归一化时，与NORM相比，HYP在前臂的LDF值趋于更高（条件效应，P = 0.05），但在背部没有差异（P = 0.19）。尽管低氧状态下SkBF可能更大，但各条件下的P 并无差异（NORM：3.67（0.35）kPa；HYP：3.46（0.39）kPa；P = 0.22）。这些发现表明，在温暖环境下运动时，低氧不会独立改变体温调节能力。
