Cerebral oxygenation is reduced during hyperthermic exercise in humans

TY - JOUR

T1 - Cerebral oxygenation is reduced during hyperthermic exercise in humans

AU - Rasmussen, Peter

AU - Nybo, Lars

AU - Volianitis, S.

AU - Møller, K.

AU - Secher, Niels H.

AU - Gjedde, Albert

AU - Rasmussen, Peter

AU - Nybo, L

AU - Volianitis, Stefanos

AU - Møller, Kirsten

AU - Secher, N H

AU - Gjedde, Albert

N1 - CURIS 2010 5200 055

PY - 2010/5/1

Y1 - 2010/5/1

N2 - Aim: Cerebral mitochondrial oxygen tension (PmitoO2) is elevated during moderate exercise, while it is reduced when exercise becomes strenuous, reflecting an elevated cerebral metabolic rate for oxygen (CMRO 2) combined with hyperventilation-induced attenuation of cerebral blood flow (CBF). Heat stress challenges exercise capacity as expressed by increased rating of perceived exertion (RPE). Methods: This study evaluated the effect of heat stress during exercise on PmitoO2 calculated based on a Kety-Schmidt-determined CBF and the arterial-to-jugular venous oxygen differences in eight males [27 ± 6 years (mean ± SD) and maximal oxygen uptake (VO2max) 63 ± 6 mL kg-1 min-1]. Results: The CBF, CMRO2 and PmitoO 2 remained stable during 1 h of moderate cycling (170 ± 11 W, ∼50% of VO2max, RPE 9-12) in normothermia (core temperature of 37.8 ± 0.4 °C). In contrast, when hyperthermia was provoked by dressing the subjects in watertight clothing during exercise (core temperature 39.5 ± 0.2 °C), PmitoO2 declined by 4.8 ± 3.8 mmHg (P < 0.05 compared to normothermia) because CMRO 2 increased by 8 ± 7% at the same time as CBF was reduced by 15 ± 13% (P < 0.05). During exercise with heat stress, RPE increased to 19 (19-20; P < 0.05); the RPE correlated inversely with P mitoO2 (r2 = 0.42, P < 0.05). Conclusion: These data indicate that strenuous exercise in the heat lowers cerebral P mitoO2, and that exercise capacity in this condition may be dependent on maintained cerebral oxygenation.

AB - Aim: Cerebral mitochondrial oxygen tension (PmitoO2) is elevated during moderate exercise, while it is reduced when exercise becomes strenuous, reflecting an elevated cerebral metabolic rate for oxygen (CMRO 2) combined with hyperventilation-induced attenuation of cerebral blood flow (CBF). Heat stress challenges exercise capacity as expressed by increased rating of perceived exertion (RPE). Methods: This study evaluated the effect of heat stress during exercise on PmitoO2 calculated based on a Kety-Schmidt-determined CBF and the arterial-to-jugular venous oxygen differences in eight males [27 ± 6 years (mean ± SD) and maximal oxygen uptake (VO2max) 63 ± 6 mL kg-1 min-1]. Results: The CBF, CMRO2 and PmitoO 2 remained stable during 1 h of moderate cycling (170 ± 11 W, ∼50% of VO2max, RPE 9-12) in normothermia (core temperature of 37.8 ± 0.4 °C). In contrast, when hyperthermia was provoked by dressing the subjects in watertight clothing during exercise (core temperature 39.5 ± 0.2 °C), PmitoO2 declined by 4.8 ± 3.8 mmHg (P < 0.05 compared to normothermia) because CMRO 2 increased by 8 ± 7% at the same time as CBF was reduced by 15 ± 13% (P < 0.05). During exercise with heat stress, RPE increased to 19 (19-20; P < 0.05); the RPE correlated inversely with P mitoO2 (r2 = 0.42, P < 0.05). Conclusion: These data indicate that strenuous exercise in the heat lowers cerebral P mitoO2, and that exercise capacity in this condition may be dependent on maintained cerebral oxygenation.

U2 - 10.1111/j.1748-1716.2010.02084.x

DO - 10.1111/j.1748-1716.2010.02084.x

M3 - Journal article

C2 - 20102344

SN - 1748-1708

VL - 199

SP - 63

EP - 70

JO - Acta Physiologica

JF - Acta Physiologica

IS - 1

ER -