Lower cardiac index levels relate to lower cerebral blood flow in older adults

Abstract

Objective: To assess cross-sectionally whether lower cardiac index relates to lower resting cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) among older adults.

Methods: Vanderbilt Memory & Aging Project participants free of stroke, dementia, and heart failure were studied (n = 314, age 73 ± 7 years, 59% male, 39% with mild cognitive impairment). Cardiac index (liters per minute per meter squared) was quantified from echocardiography. Resting CBF (milliliters per 100 grams per minute) and hypercapnia-induced CVR were quantified from pseudo-continuous arterial spin-labeling MRI. Linear regressions with ordinary least-square estimates related cardiac index to regional CBF, with adjustment for age, education, race/ethnicity, Framingham Stroke Risk Profile score (systolic blood pressure, antihypertensive medication use, diabetes mellitus, current cigarette smoking, left ventricular hypertrophy, prevalent cardiovascular disease [CVD], atrial fibrillation), APOE ε4 status, cognitive diagnosis, and regional tissue volume.

Results: Lower cardiac index corresponded to lower resting CBF in the left (β = 2.4, p = 0.001) and right (β = 2.5, p = 0.001) temporal lobes. Results were similar when participants with prevalent CVD and atrial fibrillation were excluded (left temporal lobe β = 2.3, p = 0.003; right temporal lobe β = 2.5, p = 0.003). Cardiac index was unrelated to CBF in other regions assessed (p > 0.25) and CVR in all regions (p > 0.05). In secondary cardiac index × cognitive diagnosis interaction models, cardiac index and CBF associations were present only in cognitively normal participants and affected a majority of regions assessed with effects strongest in the left (p < 0.0001) and right (p < 0.0001) temporal lobes.

Conclusions: Among older adults without stroke, dementia, or heart failure, systemic blood flow correlates with cerebral CBF in the temporal lobe, independently of prevalent CVD, but not CVR.

Figure 1. Study inclusion and exclusion details

Missing data categories are mutually exclusive. Missing covariate data include 1 participant missing left ventricular hypertrophy data and 1 participant missing atrial fibrillation data. Missing ASL challenge data (affecting CVR calculations) include participants unable to wear the nonrebreathing mask or for whom the nonrebreathing mask did not fit properly. Interaction and stratified results for resting CBF models included 164 participants with NC and 124 with MCI. Interaction and stratified results for CVR models included 120 participants with NC and 85 with MCI. ASL = arterial spin labeling; CBF = cerebral blood flow; CVD = cardiovascular disease; CVR = cerebrovascular reactivity; MCI = mild cognitive impairment; NC = normal cognition.

Figure 2. Resting CBF (A and B) and challenge CBF (C and D) maps for participants in the lowest and highest quartiles of cardiac index

Low and high cardiac index images were created with the unadjusted group mean image of the Memory & Aging Project participants with CBF analyses (n = 314) or cerebrovascular reactivity analyses (n = 221) in the lowest or highest cardiac index quartile. For illustration purposes only. CBF = cerebral blood flow.

Figure 3. Cardiac index and resting CBF in the (A) left and (B) right temporal lobes for total sample

Solid black line reflects unadjusted values of CBF outcomes (y-axis) corresponding to cardiac index (x-axis). Shading reflects 95% confidence interval. CBF = cerebral blood flow.