Measurement and analysis of blood flow velocity waveforms in the middle cerebral artery under posture change and exercise.

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The blood flow velocities in the middle cerebral artery (MCA) were measured under exercise as well as posture change using the transcranial Doppler ultrasound velocimeter. The peak-systolic velocity was found to rise markedly under exercise, while the end-diastolic velocity tended to remain at resting value. The relationship between peak-systolic velocity and systolic blood pressure, and that between peak-systolic velocity and heart rate were found to show statistically significant correlation. The mean MCA blood velocity also showed significant correlation with mean arterial pressure and heart rate. The fluctuations of velocity and resistance index were calculated in order to evaluate the hemodynamic load on the vessel wall ; these also increased markedly under exercise. Such hemodynamic changes in activity might be important in understanding the genesis of vascular diseases as well as the physiology of cerebral circulation.