Blood flow velocity waveforms in the middle cerebral artery during cycle exercise and recovery

The blood flow velocity waveforms in the middle cerebral artery (MCA) were measured under incremental cycle exercises and following recovery using the transcranial Doppler ultrasound velocimeter. At rest, the flow waveform in the MCA is characterized by a high forward flow at end-diastole, which is as much as half peak-systolic velocity. The peak-systolic velocity V _s was found to markedly rise in proportion with exercise intensity under mild and moderate intensities (up to 110 W) of exercise, while it tended to keep constant values under higher exercise intensities (above 110 W). The end-diastolic velocities V _d showed no significant change under mild exercise intensity and gradually increased under moderate exercise intensities. It was also found that the V _d values decreased more rapidly than V _s in the recovery phase. Such nonlinear changes in V _s and V _d indicate that the influence of exercise on cerebral blood flow is more complicated than previously thought.