Cerebral blood flow velocities during orthostasis and physical exercise.

The peak flow velocities in the middle cerebral artery were continuously recorded by transcranial Doppler sonography in 29 children. Arterial blood pressure and heart rates were measured every minute. The values observed during orthostasis and physical exercise were compared to baseline values obtained in the supine position. During orthostasis the velocities were, on average, reduced to 87%-94%, the minimal values being 75%-78% of the baseline values. The heart rate increased whereas blood pressure showed only minor alterations. Upon standing up the systolic peak flow velocity remained unchanged while the mean- and enddiastolic peak flow velocities decreased to 66% and 39% respectively. On average, the velocities increased to 103%-108% during physical exercise. Systolic blood pressure increased to the same extent, the heart rate even more. Continuous recording of cerebral blood flow velocities may be more useful than intermittent measurements of blood pressure to differentiate children with and without symptoms of orthostasis.