The goal of this study was to evaluate the visual evoked response in posterior cerebral artery (PCA) by means of functional transcranial doppler in patients with severe carotid disease and to determine the hemodynamic effect of severe carotid disease on posterior circulation. Measurements were performed successively in the dark and during the white light stimulation in 49 patients with high-grade (70–99%) internal carotid artery (ICA) stenosis or occlusion and compared with 30 healthy age and sex matched subjects. Mean blood flow velocities (MBFV) (cm/s±2SD) and mean reaction time (MRT) (s±2SD) during three consecutive repetitive periods of 1 minute each were analyzed. MBFV in PCA during the white light stimulation and in the dark between the two groups didn’t differ. MRT in patients showed a significantly prolonged visual evoked response in both affected (light: patients 29.36±14.46, controls 19.67±11.25, respectively, p<0.046; dark: patients 35.25±11.9, controls 21.89±10.31, respectively, p<0.002 and unaffected side (dark: patients 33.13±11.12, controls 23.89±11.23, respectively, p<0.032) of ICA. This data showed that MRT is the principal restrictive factor in the case of carotid stenosis suggesting the independence of cerebral vascular reserve capacity of the posterior part of Willis circle that is necessary to be considered separately
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