Developing pulsatile flow in the internal carotid artery

Laser Doppler velocity measurements were performed on developing pulsatile flow in a strongly curved tube under flow conditions characteristic of the blood flow in the internal carotid artery called the siphon portion (curvature ratio of 1/2 , Womersley parameter of 5.5 and peak Dean number of 750). The isovelocity contours of the axial direction show the flow development which is similar to the steady flow in a strongly curved tube with a fully developed inlet profile. However it is dissimilar to the steady flow in which imbedded secondary-flow helical motions occur within a large clockwise vortex (Dean type). During the deceleration phase, the reverse axial flow occurs near the inner side of the curvature. The appearance of reverse axial flow contributes to the oscillatory shear index (OSI). The values of OSI, which evaluate the reversed wall shear stress, increase with flow development at the inner side of the curvature and approach zero at the outer side of the curvature. These results show that the values of OSI are higher at the site of the atherosclerotic regions (fibrous plaques or localized cloudy thickening) found in the human internal carotid artery.