期刊
JOURNAL OF PHYSIOLOGY-LONDON
卷 534, 期 1, 页码 279-286出版社
WILEY
DOI: 10.1111/j.1469-7793.2001.t01-1-00279.x
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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) over dot (O2,max)) 70 +/- 1 ml min(-1) kg(-1) (mean +/- S.E.M.)) performed two exercise trials at 57 % of (V) over dot (O2,max) on a cycle ergometer in a hot (40 degreesC; hyperthermic trial) and in a thermoneutral environment (18 degreesC; control trial). In the hyperthermic trial, the oesophageal temperature increased throughout the exercise period reaching a peals. value of 40.0 +/- 0.1 degreesC 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 degreesC after similar to 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,P-CO2) obtained during preliminary exercise tests were used to account for the differences in P-a,P-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,P-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.
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