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Cerebral oxygenation is reduced during hyperthermic exercise in humans
Author(s) -
Rasmussen P.,
Nybo L.,
Volianitis S.,
Møller K.,
Secher N. H.,
Gjedde A.
Publication year - 2010
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2010.02084.x
Subject(s) - hyperventilation , cerebral blood flow , core temperature , hyperthermia , medicine , heart rate , rating of perceived exertion , anesthesia , vo2 max , heat stress , oxygen , chemistry , blood pressure , zoology , organic chemistry , biology
Aim: Cerebral mitochondrial oxygen tension ( P mito O 2 ) 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 P mito O 2 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 ( V O 2max ) 63 ± 6 mL kg −1 min −1 ]. Results: The CBF, CMRO 2 and P mito O 2 remained stable during 1 h of moderate cycling (170 ± 11 W, ∼50% of V O 2max , 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), P mito O 2 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 mito O 2 ( r 2 = 0.42, P < 0.05). Conclusion: These data indicate that strenuous exercise in the heat lowers cerebral P mito O 2 , and that exercise capacity in this condition may be dependent on maintained cerebral oxygenation.