TY - JOUR

T1 - Whole body hyperthermia, but not skin hyperthermia, accelerates brain and locomotor limb circulatory strain and impairs exercise capacity in humans

AU - Trangmar, Steven J

AU - Chiesa, Scott T

AU - Kalsi, Kameljit K

AU - Secher, Niels H

AU - González-Alonso, José

N1 - © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

PY - 2017/1

Y1 - 2017/1

N2 - Cardiovascular strain and hyperthermia are thought to be important factors limiting exercise capacity in heat-stressed humans, however, the contribution of elevations in skin (Tsk) versus whole body temperatures on exercise capacity has not been characterized. To ascertain their relationships with exercise capacity, blood temperature (TB), oxygen uptake (V̇O2), brain perfusion (MCA Vmean), locomotor limb hemodynamics, and hematological parameters were assessed during incremental cycling exercise with elevated skin (mild hyperthermia; HYPmild), combined core and skin temperatures (moderate hyperthermia; HYPmod), and under control conditions. Both hyperthermic conditions increased Tsk versus control (6.2 ± 0.2°C; P < 0.001), however, only HYPmod increased resting TB, leg blood flow and cardiac output (Q̇), but not MCA Vmean Throughout exercise, Tsk remained elevated in both hyperthermic conditions, whereas only TB was greater in HYPmod At exhaustion, oxygen uptake and exercise capacity were reduced in HYPmod in association with lower leg blood flow, MCA Vmean and mean arterial pressure (MAP), but similar maximal heart rate and TB 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.

AB - Cardiovascular strain and hyperthermia are thought to be important factors limiting exercise capacity in heat-stressed humans, however, the contribution of elevations in skin (Tsk) versus whole body temperatures on exercise capacity has not been characterized. To ascertain their relationships with exercise capacity, blood temperature (TB), oxygen uptake (V̇O2), brain perfusion (MCA Vmean), locomotor limb hemodynamics, and hematological parameters were assessed during incremental cycling exercise with elevated skin (mild hyperthermia; HYPmild), combined core and skin temperatures (moderate hyperthermia; HYPmod), and under control conditions. Both hyperthermic conditions increased Tsk versus control (6.2 ± 0.2°C; P < 0.001), however, only HYPmod increased resting TB, leg blood flow and cardiac output (Q̇), but not MCA Vmean Throughout exercise, Tsk remained elevated in both hyperthermic conditions, whereas only TB was greater in HYPmod At exhaustion, oxygen uptake and exercise capacity were reduced in HYPmod in association with lower leg blood flow, MCA Vmean and mean arterial pressure (MAP), but similar maximal heart rate and TB 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.

KW - Adenosine Triphosphate/blood

KW - Adult

KW - Blood Gas Analysis

KW - Blood Pressure

KW - Body Temperature

KW - Brain/blood supply

KW - Catecholamines/blood

KW - Exercise

KW - Fever/metabolism

KW - Heart Rate

KW - Heat-Shock Response

KW - Hemodynamics

KW - Humans

KW - Leg/blood supply

KW - Male

KW - Middle Cerebral Artery/physiopathology

KW - Oxygen Consumption

KW - Skin Physiological Phenomena

KW - Young Adult

U2 - 10.14814/phy2.13108

DO - 10.14814/phy2.13108

M3 - Journal article

C2 - 28108645

VL - 5

JO - Physiological Reports

JF - Physiological Reports

SN - 2051-817X

IS - 2

M1 - e13108

ER -