Cognitive Impairment Correlates Linearly with Mean Flow Velocity by Transcranial Doppler below a Definable Threshold

Abstract

Introduction: Low cerebral blood flow can affect cognition in patients with high-grade asymptomatic internal carotid artery stenosis. Current clinical algorithms use stroke risk to determine which patients should undergo revascularization without considering cognitive decline. Although correlations between low-flow and cognitive impairment have been reported, it is not known whether a threshold exists below which such a correlation expresses itself. Such information would be critical in treatment decisions about whether to intervene in patients with high-grade carotid artery stenosis who are at risk for cognitive decline. Objective: To determine how reduced blood flow correlates with lower cognitive scores. Methods: Patients 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. Results: Forty-two patients with unilateral high-grade internal carotid artery stenosis without stroke were enrolled (26 males, age = 74 ± 9 years, education = 16 ± 3 years). Average composite Z-score was -0.31 SD below the age-specific normative mean (range -2.8 to +1.2 SD). In linear regression adjusted for age, education, and depression, MFV correlated with cognitive Z-score (β = 0.308, p = 0.043). A single breakpoint in the range of composite Z-scores was identified at 45 cm/s. For MFV < 45 cm/s, Z-score decreased 0.05 SD per cm/s MFV (95% CI: 0.01-0.10). For MFV > 45 cm/s, Z-score change was nonsignificant (95% CI: -0.07 to 0.05). Conclusions: In high-grade, asymptomatic carotid artery stenosis, cognitive impairment correlated linearly with lower flow in the hemisphere fed by the occluded internal carotid artery, but only below a threshold of MFV = 45 cm/s. Identifying a hemodynamic threshold for cognitive decline using a simple, noninvasive method may influence revascularization decision-making in otherwise "asymptomatic" carotid disease.

Assessment of the Willis circle flow changes and the severity of degenerative aortic stenosis and cognitive impairment

“…In Kidher et al study of 56 patients with severe DAS, aortic stiffness (assessed by measuring carotid-femoral pulse wave velocity) was an indicator for preoperative cognitive dysfunction [12]. This data were supported by the results of the observational study in a group of 42 patients with high-grade, asymptomatic carotid artery stenosis, in which cognitive impairment correlated linearly with mean flow velocity below a threshold of < 45 cm/s in the hemisphere fed by the stenosed internal carotid artery [30]. In line, carotid artery stenosis may be associated with mild cognitive impairment in either neurologically symptomatic and asymptomatic patients [26,33].…”

“…The other common believe is that CBF or cerebral flow velocity should correlate with cognitive status [30][31][32]. However, prior studies have only partially quantified the nature of the cognition-hemodynamic relationship [31,32].…”

Editor's Choice – Asymptomatic Carotid Stenosis and Cognitive Impairment: A Systematic Review

“…35 Another study (which did not evaluate CVR) reported that the composite z score for cognitive performance decreased linearly below an MCAV of 45 cm/sec. 27 This level of reduced MCAV is more commonly seen in patients with a non-functioning CoW and impaired CVR.…”

Glucose Fluctuation and Severe Internal Carotid Artery Siphon Stenosis in Type 2 Diabetes Patients

“…Carotid artery stenosis was evaluated according to the North American Symptomatic Carotid Endarterectomy Trial method [ 17 ]. Patients with ≥80% carotid artery stenosis [ 18 ] or those undergoing renal replacement therapy [ 19 ] were excluded because these conditions could affect cognitive function. Additionally, those taking antidementia drugs or having underlying comorbidities affecting cognitive function (depression, thyroid dysfunction, and vitamin B1, vitamin B12, and folate deficiency) were excluded.…”