Regional cerebral blood flow in man at rest and during exercise.

Regional cerebral blood flow (rCBF) of the left hemisphere was measured in 12 healthy young men at rest and during physical work on a bicycle ergometer in the supine position at work-load levels of 25 W or 100 W using the intravenous 133Xe method. Regional mean cerebral blood flow, regional gray-matter flow, and relative gray-matter weight was determined for six regions of interest. Arterial blood pressure, pulse frequency and expiratory CO2 concentration were recorded. Cerebral blood flow in all regions was significantly (P less than 0.001) higher during exercise than at rest. The increase in the 100 W group (24.7%) was significantly (P less than 0.05) greater than in the 25 W group (13.5%), but resting blood flow levels and alveolar CO2 concentrations were also different in both groups. Mean arterial blood pressure, pulse frequency and alveolar CO2 concentrations, but not arterial pCO2, were significantly higher during exercise and there was a faster washout of whole-body xenon. The CBF increase was interpreted as a combined effect of elevated systemic blood pressure and functionally activated brain metabolism. There was no evidence of impaired cerebral autoregulation.