Effect of internal carotid artery occlusion on vertebral artery blood flow: a duplex ultrasonographic evaluation.

The aim of this study was to evaluate the effect of unilateral internal carotid artery occlusion on blood flow volume and blood flow velocities in both vertebral arteries using duplex Doppler ultrasonography in the cervical segment. Forty patients with unilateral extracranial internal carotid artery occlusion confirmed by angiography were studied, and the results were compared with those obtained in 57 age-matched patients in whom cervical duplex ultrasonography showed no abnormalities. We measured the diameter, flow velocities, and blood flow volume in both vertebral arteries, and the side-to-side differences were also calculated. Eleven patients (27.5%) with an occluded internal carotid artery had increased peak systolic velocity in the ipsilateral vertebral artery, and 6 (15%) had increased peak systolic velocity in the contralateral vertebral artery. The mean peak systolic velocity and the mean blood flow volume were statistically greater in the ipsilateral vertebral arteries than in the same-side vertebral arteries of the control group (P < .05). We also detected a mean increase of 14.29% of the net blood flow volume in the vertebral arteries compared with the control group. Patients with extracranial unilateral internal carotid artery occlusion may have a compensatory increase in both the peak systolic velocity and the blood flow volume in both vertebral arteries.