Cerebral oxygenation is reduced during hyperthermic exercise in humans

P. Rasmussen, L. Nybo, S. Volianitis, K. Møller, N. H. Secher, A. Gjedde

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)63-70
Number of pages8
JournalActa Physiologica
Volume199
Issue number1
DOIs
StatePublished - May 1 2010

Keywords

  • Central fatigue
  • Cerebral blood flow
  • Hyperthermia
  • Oxygen tension

ASJC Scopus subject areas

  • Physiology

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