Side-to-side differences and day-to-day variations of transcranial Doppler parameters in normal subjects.

We investigated 35 normal adults to assess variations in cerebral artery blood velocities, hemispheric blood velocity ratios, and pulsatility indices, both with regard to changes between the sides and between days. We found no significant variations between sides or days. Changes from one day to the next exceeding 20% in blood velocity in the middle cerebral artery (VMCA), the anterior cerebral artery (VACA), the distal extracranial internal carotid artery (VICA), and in the hemispheric VMCA/VICA, VACA/VICA, or VACA/VMCA ratios, may be considered significant at the 95% level.