Lower diastolic velocity in the internal carotid artery mediates lower cerebral blood flow with age.

Advanced aging is characterized by reduced cerebral blood flow (CBF) and increased central arterial stiffness. Increased arterial stiffness is associated with increased CBF pulsatility, which is detrimental to cerebrovascular integrity. We examined the associations between central arterial stiffness, diastolic, systolic, and total CBF in healthy cognitively normal subjects (n = 163, age 20-81 yr, 62% female) who underwent color-coded duplex ultrasonography of the internal carotid (ICA) and the vertebral artery (VA) to measure pulsatile CBF and total CBF. Cerebral tissue oxygenation was measured using near-infrared spectroscopy (NIRS). Carotid β-stiffness index and carotid-femoral pulse wave velocity (cfPWV) were assessed via applanation tonometry and ultrasonography to assess central artery stiffness. Age was negatively associated with total CBF (R2 = 0.268, P < 0.001). ICA diastolic velocity was negatively associated with cfPWV (R2 = 0.163, P < 0.001) and carotid β-stiffness index (R2 = 0.134, P < 0.001). Higher carotid β-stiffness index was associated with lower CBF with age, which was mediated through lower ICA diastolic velocity. These findings suggest that central arterial stiffness with age may lead to reductions in ICA diastolic velocity, contributing to a reduction in CBF.NEW & NOTEWORTHY In this study, we demonstrated that higher central arterial stiffness is associated with lower diastolic velocity of the ICA, which mediates lower CBF with age. These findings provide new mechanistic insights into the reduction in CBF with age and add to the mounting evidence for the importance of age-related central arterial stiffening in brain health.