Differences in near-wall shear rate in the carotid artery within subjects are associated with different intima-media thicknesses

In the common carotid artery, reflections originating from the periphery an d the flow divider may affect the shape of the flow velocity profile and, h ence, near-wall shear rate (WSR) differently just before the bifurcation (l ocation B) than 20 to 30 mm farther upstream (location A). Recent developme nts in ultrasound technology allow the assessment of WSR and intima-media t hickness (IMT) at the same site in the carotid artery in vivo. We therefore determined WSR at locations A and B and investigated whether the differenc es between both sites, if any, were associated with different IMTs and diff erent mechanical properties of the arterial wall. The effect of age on the possible differences was assessed as well. The study was performed on presu mably healthy volunteers (n=53). In all individuals, IMT was larger at loca tion B than at location A. The relative difference in IMT between both loca tions was not affected by age. No significant differences in diameter and d istension were found between locations. Near peak systolic and near mean WS R at the posterior wall (PWSRp and MWSRp, respectively) were significantly lower at location B than at location A. The relative differences in PWSRp a nd MWSRp between both locations within subjects were independent of age. Th e velocity profiles were more blunted at location A than at location B. PWS Rp and MWSRp significantly decreased and IMT significantly increased with a ge at both locations. IMT was negatively correlated with PWSRp and MWSRp at location B, but this correlation was not significant at location A. In sum mary, in the common carotid artery, the lower WSR near the bifurcation, as compared with 20 to 30 mm upstream, is associated with a larger IMT than at the more proximal site. The relative difference between both locations wit hin subjects is independent of age.