IMPAIRED DYNAMIC CEREBRAL AUTOREGULATION IN CAROTID-ARTERY STENOSIS

Background and Purpose If it could be determined whether cerebral bloo d flow can be maintained (autoregulated) during transient ails in arte rial blood pressure, we might be able to identity patients with caroti d stenosis who are al risk of stroke. However, conventional methods of determining autoregulation in such patients are invasive and/or expen sive. Methods We used a new noninvasive method to estimate dynamic cer ebral autoregulation in 27 patients with carotid stenosis and 21 age-m atched normal controls. After a stepwise fall in arterial blood pressu re, we determined the rate of rise of middle cerebral artery blood flo w velocity compared with that of arterial blood pressure. We compared the method with a conventional method of determining cerebral hemodyna mics, CO2 reactivity. Results Autoregulatory index (ARI) was significa ntly reduced in middle cerebral arteries ipsilateral to a stenosed/occ luded carotid artery: mean+/-SD 3.3+/-2.2 compared with normal control s (6.3+/-1.1; P<.0001) and nonstenosed carotid arteries in patients (5 .9+/-2.1; P<.002). A subgroup of patients with severe impairment was i dentified. ARI returned to normal after carotid endarterectomy was per formed. In a number of cases, ARI was impaired in the presence of CO2 reactivity. Conclusions This simple technique allows identification of impaired autoregulation in patients with carotid artery disease. It m ay allow identification of patients at risk from transient Tails of bl ood pressure as may occur at the onset of antihypertensive therapy and during surgery, It. may allow a subgroup of patients with asymptomati c carotid stenosis who are at risk of hemodynamic stroke to be identif ied.