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Effect of exercise on cerebral perfusion in humans at high altitude

¹Coventry and Warwickshire County Vascular Unit, University Hospitals Coventry and Warwickshire National Health Service Trust, Coventry; ²QinetiQ, Farnborough; ³Nuffield Department of Anesthetics, University of Oxford, John Radcliffe Hospital, Headley Way, Headington, Oxford; ⁴The Medical School, University of Birmingham, Birmingham; and ⁵ScanMed Medical Instruments, Moreton-in-the-Marsh, United Kingdom

Submitted 3 September 2004 ; accepted in final form 1 April 2005

The effects of submaximal and maximal exercise on cerebral perfusion were assessed using a portable, recumbent cycle ergometer in nine unacclimatized subjects ascending to 5,260 m. At 150 m, mean (SD) cerebral oxygenation (rSO₂%) increased during submaximal exercise from 68.4 (SD 2.1) to 70.9 (SD 3.8) (P < 0.0001) and at maximal oxygen uptake (O_{2 max}) to 69.8 (SD 3.1) (P < 0.02). In contrast, at each of the high altitudes studied, rSO₂ was reduced during submaximal exercise from 66.2 (SD 2.5) to 62.6 (SD 2.1) at 3,610 m (P < 0.0001), 63.0 (SD 2.1) to 58.9 (SD 2.1) at 4,750 m (P < 0.0001), and 62.4 (SD 3.6) to 61.2 (SD 3.9) at 5,260 m (P < 0.01), and at O_{2 max} to 61.2 (SD 3.3) at 3,610 m (P < 0.0001), to 59.4 (SD 2.6) at 4,750 m (P < 0.0001), and to 58.0 (SD 3.0) at 5,260 m (P < 0.0001). Cerebrovascular resistance tended to fall during submaximal exercise (P = not significant) and rise at O_{2 max}, following the changes in arterial oxygen saturation and end-tidal CO₂. Cerebral oxygen delivery was maintained during submaximal exercise at 150 m with a nonsignificant fall at O_{2 max}, but at high altitude peaked at 30% of O_{2 max} and then fell progressively at higher levels of exercise. The fall in rSO₂ and oxygen delivery during exercise may limit exercise at altitude and is likely to contribute to the problems of acute mountain sickness and high-altitude cerebral edema.

maximal oxygen uptake; cerebral oxygenation; cerebral blood flow; cerebrovascular resistance; cerebral oxygen delivery

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