Patterns of cerebrovascular reactivity in patients with unilateral asymptomatic carotid artery stenosis

Abstract

Background and Purpose Intracranial hemodynamic status varies in patients with unilateral significant carotid artery stenosis. It ranges from normal, because of sufficient collater­als, to poor, because of a severely reduced blood supply that puts the patient at an increased risk of stroke or cerebral ischemia. The present study examined patterns of abnormal cerebrovascular hemodynamics in patients with asymptomatic carotid artery stenosis. Methods The C02 reactivity of the cerebral resistance index (CRi) and of mean blood flow velocity (vmean) was determined via transcranial Doppler sonography in 91 patients with unilateral high-grade to threadlike carotid artery stenosis and in 37 control subjects. The interhemispheric asymmetry of CR1 reactivity of the control group was used to differentiate between normal and abnormal findings. Results We found that 64.8% of the patients demonstrated normal CR1 asymmetry with comparable CR1 reactivity (ipsilat­eral, 4.42±0.44 %CR1/vol%CO2; contralateral, 4.51 ±0.39 %CR1/vol%CO2) and vmean reactivity (ipsilateral, 0.080±0.004 m/s per vol%CO2; contralateral, 0.079 ± 0.005 m/s per vol%CO2) at both hemispheres. In 16.5% of the patients, CR1 reactivity was supranormal at the affected hemisphere. This phenomenon was due to an exaggerated dilatory response of the ipsilateral hemisphere and was combined with an absent CR1 reactivity of the contralateral hemisphere (ipsilateral, 6.63±1.03 %CR1/ vol%CO2; contralateral, −1.16± 1.78 %CR1/vol%CO2). In con­trast, hemispheric vmean reactivities were comparable (ipsilateral, 0.078±0.008 m/s per vol%CO2; contralateral, 0.077±0.008 m/s per vol%CO2). The remaining 18.7% showed severely dimin­ished ipsilateral CR1 reactivity (ipsilateral, 1.91±0.83 %CR1/ vol%CO2; contralateral, 8.48±1.00 %CR1/vol%CO2) and vmean reactivity (ipsilateral, 0.073 ±0.007 m/s per vol%CO2; contralat­eral, 0.108±0.012 m/s per vol%CO2; P