Regional cerebral artery mean flow velocity and blood flow during dynamic exercise in humans

Transcranial Doppler ultrasound-determined middle (MCA) and anterior (ACA) cerebral artery mean flow velocities (Vmean) and pulsatility indexes (PI) were measured during "no-load" 21, 60, and 102 revolutions/min (rpm) and loaded cycling (30, 60, and 149 W) at approximately 60 rpm. At rest Vmean MCA was 51 (36-55) cm/s (median and range; n = 10) and Vmean ACA was 41 (36-49) cm/s (n = 7; P < 0.05). With no load on the cycle Vmean MCA increased 4 (2-36), 10 (0-47), and 27% (4-58) (P < 0.05) at the three pedaling frequencies, respectively; arterial PCO2 (PaCO2) remained constant. During loaded cycling the increases were 19 (6-42), 25 (2-45), and 32% (12-67) (P < 0.01), respectively, with only a minimal change in PaCO2. No significant changes were observed in Vmean ACA. Changes in Vmean MCA were similar to those recorded by the initial slope index (ISI) of the 133Xe clearance method (n = 11), which in turn were smaller than increases recorded by the fast-compartment flow. PI ACA followed PI MCA during no-load as well as loaded exercise and increased with work rate, perhaps reflecting an increase in pulse pressure from 56 (48-63) mmHg at rest to 109 (88-123) mmHg at 149 W (P < 0.01). Data demonstrate a graded increase in regional cerebral perfusion during dynamic exercise corresponding to the MCA territory.