Whole body hyperthermia, but not skin hyperthermia, accelerates brain and locomotor limb circulatory strain and impairs exercise capacity in humans

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• 作者：Steven J. Trangmar ; Scott T. Chiesa ; Kameljit K. Kalsi ; Niels H. Secher ; José González‐Alonso
• 刊名：Physiological Reports
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：5
• 期：2
• 全文大小：1.3MB
• ISSN：2051-817X

文摘

Cardiovascular strain and hyperthermia are thought to be important factors limiting exercise capacity in heat-stressed humans, however, the contribution of elevations in skin (T_sk) versus whole body temperatures on exercise capacity has not been characterized. To ascertain their relationships with exercise capacity, blood temperature (T_B), oxygen uptake (V̇O₂), brain perfusion (MCA V_mean), locomotor limb hemodynamics, and hematological parameters were assessed during incremental cycling exercise with elevated skin (mild hyperthermia; HYP_mild), combined core and skin temperatures (moderate hyperthermia; HYP_mod), and under control conditions. Both hyperthermic conditions increased T_sk versus control (6.2 ± 0.2°C; P < 0.001), however, only HYP_mod increased resting T_B, leg blood flow and cardiac output (Q̇), but not MCA V_mean. Throughout exercise, T_sk remained elevated in both hyperthermic conditions, whereas only T_B was greater in HYP_mod. At exhaustion, oxygen uptake and exercise capacity were reduced in HYP_mod in association with lower leg blood flow, MCA V_mean and mean arterial pressure (MAP), but similar maximal heart rate and T_B. The attenuated brain and leg perfusion with hyperthermia was associated with a plateau in MCA and two-legged vascular conductance (VC). Mechanistically, the falling MCA VC was coupled to reductions in PaCO₂, whereas the plateau in leg vascular conductance was related to markedly elevated plasma [NA] and a plateau in plasma ATP. These findings reveal that whole-body hyperthermia, but not skin hyperthermia, compromises exercise capacity in heat-stressed humans through the early attenuation of brain and active muscle blood flow.