Carotid Blood Flow Assessment during Dynamic Respiratory Maneuvers Demonstrates a Shift toward Vasoconstriction with...

Internal carotid artery (ICA) blood flow may be an alternative target to measure cerebrovascular reactivity (CVR) and endothelium-dependent vasodilatory dysfunction. We investigated the feasibility of testing CVR in the ICA during routine clinical carotid investigation.

CVR was assessed by effects of breath-hold (BH) and rapid-breathing (RB) on ICA diameter, blood velocities (peak systolic velocity [PSV], end diastolic velocity [EDV], and mean velocity [MV]), volume flow, and relative to changes in end-tidal carbon dioxide (end-tidal CO₂ [etCO₂]; CVR_PSV, CVR_EDV, CVR_MV, and CVR_Flow). Feasibility and validity were determined by data quality, agreement between challenges, and association with age.

In 50 patients (68 ± 13 years old, 15 female), recordings during rest, BH, and RB were of good quality in 96%, 90%, and 88%, respectively. Age-related reductions in blood velocities were evident during rest (EDV: r ² = 0.37, P < 0.0001), BH (EDV: r ² = 0.42, P < 0.001), and RB (EDV, r ² = 0.50, P < 0.0001). During BH, the absolute changes in blood velocities (EDV: r ² = 0.15, P < 0.01), etCO₂ (r ² = 0.10, P = 0.03), CVR_EDV (r ² = 0.13, P = 0.02), and CVR_MV (r ² = 0.11, P = 0.03) were smaller in older patients. In contrast, during RB, absolute changes in blood velocities and etCO₂ were not age related, but changes in volume flow (r ² = 0.12, P = 0.02), CVR_MV (r ² = 0.11, P = 0.03), and CVR_Flow (r ² = 0.16, P < 0.01) were greater in older patients.

During routine carotid duplex assessment, assessing CVR in the ICA was feasible, practical, and associated with high quality recordings. Differential associations with age between hypercapnic and hypocapnic stimuli imply a greater tendency to vasoconstriction in older patients.