Quantitative analysis of effects of hemodynamic stress on temporal variations of cardiac phases in models of human carotid bulbs

In this study, we evaluated the hemodynamics of carotid artery models with carotid bulbs of various sizes using computational fluid dynamics (CFD) and the Fluent CFD software. The oscillatory shear index (OSI) and flow velocity distribution were evaluated in carotid models without a carotid bulb and with carotid bulbs of known geometry (major axis of 10, 11, 12, 13, and 14 mm; carotid bifurcation angle of 50°). Furthermore, the diameters of the common carotid artery, the external carotid artery, and the internal carotid artery were defined as 7.2, 4.0, and 4.5 mm, respectively. The accuracy of the CFD analysis in this study was verified using a flow phantom and measuring velocities with phase-contrast cine magnetic resonance imaging. The CFD parameters were defined as follows: rigid and no-slip walls, pulsatile flow, and 0 Pa of peripheral pressure. The OSI in the carotid bulb tended to show a high value during the expansion of the carotid bulb (maximum and minimum OSI: 0.11 ± 0.08 at d_bulb: 14 mm; 0.0013 ± 0.0011 at no bulb), and the region of high OSI expanded with the expansion of the carotid bulb. The flow separated near the carotid bulb, and the flow deceleration expanded downstream as the size of the bulb increased. These findings suggest that the size of the carotid bulbs contributed to the OSI because the larger bulbs exhibited higher OSI values. The relation between the OSI and the carotid bulb size could serve as a risk indicator for atherosclerosis.