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PMID: 11433008 Published · ppublish English Journal Article

Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans.

The Journal of physiology ·Vol. 534 ·No. Pt 1 ·2001-07-01 ·Pages 279-86

Nybo L, Nielsen B

Abstract

1. In the present study we examined the effect of hyperthermia on the middle cerebral artery mean blood velocity (MCA V(mean)) during prolonged exercise. We predicted that the cerebral circulation would be impaired when hyperthermia is present during exercise and assumed that this could be observed as a reduced MCA V(mean). 2. Eight endurance trained men (maximum oxygen uptake (V(O2,max)) 70 +/- 1 ml min(-1) kg(-1) (mean +/- S.E.M.)) performed two exercise trials at 57 % of V(O2,max) on a cycle ergometer in a hot (40 degrees C; hyperthermic trial) and in a thermoneutral environment (18 degrees C; control trial). In the hyperthermic trial, the oesophageal temperature increased throughout the exercise period reaching a peak value of 40.0 +/- 0.1 degrees C at exhaustion after 53 +/- 4 min of exercise. In the control trial, exercise was maintained for 1 h without any signs of fatigue and with core temperature stabilised at 37.8 +/- 0.1 degrees C after approximately 15 min of exercise. 3. Concomitant with the development of hyperthermia, MCA V(mean) declined by 26 +/- 3 % from 73 +/- 4 cm s(-1) at the beginning of exercise to 54 +/- 4 cm s(-1) at exhaustion (P < 0.001). In contrast, MCA V(mean) remained unchanged at 70-72 cm s(-1) throughout the 1 h control trial. 4. When individually determined regression lines for MCA V(mean) and arterial carbon dioxide pressure (P(a,CO2)) obtained during preliminary exercise tests were used to account for the differences in P(a,CO2) between the hyperthermic and control trial, it appeared that more than half of the reduction in MCA V(mean) (56 +/- 8 %) was related to a hyperventilation-induced drop in P(a,CO2). Declining cardiac output and arterial blood pressure accounted for the remaining part of the hyperthermia-induced reduction in MCA V(mean). 5. The present results demonstrate that the development of hyperthermia during prolonged exercise is associated with a marked reduction in MCA V(mean).

MeSH Terms
Adult Bicycling Blood Flow Velocity Body Temperature Cardiovascular System/physiopathology Cerebral Arteries/physiopathology Esophagus/physiopathology Exercise/physiology Fever/physiopathology Humans Male Physical Endurance/physiology Respiration Time Factors
Authors & Affiliations
2 authors, click to expand affiliations / ORCID
Nybo L
Department of Human Physiology, Institute of Exercise and Sport Sciences, University of Copenhagen, Denmark.
Nielsen B
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Article Info
Journal
The Journal of physiology
Abbr.
J Physiol
ISSN
0022-3751
DOI
10.1111/j.1469-7793.2001.t01-1-00279.x
Published
2001-07-01
Pages
279-86
Language
English
Region
England
NLM ID
0266262
PMCID
PMC2278686
Subset
IM
External Links
PubMed source DOI: 10.1111/j.1469-7793.2001.t01-1-00279.x PMC Full Text View journal details
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