Effect of Age on Cerebral Blood Flow Velocity in Patients After Aneurysmal Subarachnoid Hemorrhage

Abstract

To the Editor: We read with interest the article by Torbey et al1 on effect of age on cerebral blood flow velocity in patients after aneurysmal subarachnoid hemorrhage, published in the September issue of Stroke . Using conventional transcranial Doppler ultrasonography, the authors report an unexpectedly large decrease in flow velocity in the middle cerebral artery (MCA) in patients older than 68 years in comparison to those younger than 68 years. The mean flow velocity in the MCA was found to be 42 cm/s in the former and 81 cm/s in the latter group. Thus, the difference was as much as 48%, whereas elsewhere, in other large groups of healthy subjects, the range of difference was only between 17% and 22%.2,3⇓ The fact that the authors found a higher incidence of vasospasm in the younger group cannot explain the discrepancy because such significant differences in flow velocity were found at admission, ie, before the vasospasm usually develops. The authors have addressed only superficially a fundamental question: why does subarachnoid hemorrhage affect cerebral vessels in older patients differently? The problem is even more intriguing given the fact that vasoreactivity appears not to be affected by normal aging.4,5⇓ We suspect that the decline in flow velocity in reality does not need to be as substantial as the authors state. The conventional Doppler technique they used does not allow measurement of the angle of insonation of the vessel, which is crucial in their setup of the study. In young persons the horizontal portion of the MCA projects laterally toward the temporal acoustic window, whereas in older subjects it bows ventrally, which results in a wider angle of insonation.6 No exact data on the real magnitude of this angle in normal elderly subjects have been published to date. …