MIDDLE CEREBRAL-ARTERY BLOOD VELOCITY AND CEREBRAL BLOOD-FLOW AND O-2 UPTAKE DURING DYNAMIC EXERCISE

Results obtained by the Xe-133 clearance method with external detectors and by transcranial Doppler sonography (TCD) suggest that dynamic exercise causes an increase of global average cerebral blood flow (CBF). These data are contradicted by earlier data obtained during less-well-defined conditions. To investigate this controversy, we applied the Kety-Schmidt technique to measure the global average levels of CBF and cerebral metabolic rate of oxygen (CMRO2) during rest and dynamic exercise. Simultaneously with the determination of CBF and CMRO2, we used TCD to determine mean maximal flow velocity in the middle cerebral artery (MCA V(mean)). For values of CBF and MCA V(mean) a correction for an observed small drop in arterial PCO2 was carried out. Baseline values for global CBF and CMRO2 were 50.7 and 3.63 ml . 100 g-1 . min-1, respectively. The same values were found during dynamic exercise, whereas a 22% (P < 0.0001) increase in MCA V(mean) was observed. Hence, the exercise-induced increase in MCA V(mean) is not a reflection of a proportional increase in CBF.