CAROTID-ARTERY BLOOD-FLOW AND MIDDLE CEREBRAL-ARTERY BLOOD-FLOW VELOCITY DURING PHYSICAL EXERCISE

Factors controlling cerebral blood flow (CBF) during exercise are comp lex and incompletely known. Different techniques have shown partly con tradictory results of changes in regional and global cerebral perfusio n during dynamic exercise in healthy subjects. To elucidate the global CBF response to supine stepwise increasing physical exercise, we meas ured blood flow in the left common carotid artery (QCCA) and the left internal carotid artery (QICA) simultaneously with the blood flow velo city in the ipsilateral middle cerebral artery (V-MCA) using duplex ul trasonography and transcranial Doppler ultrasonography. During moderat e exercise intensity (60-67% of maximal capacity), the V-MCA increased 14% (P < 0.001), the QICA 17% (P < 0.01), and the QCCA 33% (P < 0.001 ) compared with baseline values. High physical exercise intensity (80- 90% of maximal capacity) tended to reduce V-MCA and QICA compared with moderate exercise, in contrast to a continued increase in QCCA. The r esults indicate an increased global CBF during exercise. This increase was reduced during hard exercise due to a decrease of the arterial PC O2 secondary to hyperventilation.