MethodsPatients with ≥80% unilateral internal carotid artery stenosis with no history of stroke were recruited from inpatient and outpatient practices at a single, large, comprehensive stroke center. Patients underwent bilateral insonation of middle cerebral arteries with standard 2-Hz probes over the temporal windows with transcranial Doppler. Cognitive assessments were performed by an experienced neuropsychologist using a cognitive battery comprising 14 standardized tests with normative samples grouped by age. Z-scores were generated for each test and averaged to obtain a composite Z-score for each patient. Multivariable linear regression examined associations between mean flow velocity (MFV) and composite Z-score, adjusting for age, education, and depression. The Davies test was used to determine if there was a breakpoint for a non-zero difference in slope of a segmented relationship over the range of composite Z-score values.