| Fluid dynamics and arterial geometry are believed to be important factors associated with the development of the vascular disease, atherosclerosis. The purpose of this investigation was to study experimentally how the local geometrical characteristics of an arterial bifurcation, in particular the angle of bifurcation, affect the local detailed fluid-dynamic characteristics. The study focused on a major coronary-artery bifurcation, i.e., the CFX/LAD bifurcation, as a model. The experiments employed seven excised fixed canine hearts perfused by a pulsatile pump, and involved a range of unsteady flow conditions (the Reynolds number, based on spatially and temporally averaged velocity, ranged from 100 to 450) which included those encountered physiologically. Velocity profiles from both the daughter-vessels of the bifurcation were acquired with a 20 MHz pulsed ultrasonic Doppler velocity meter. These were analyzed and are presented in terms of their skewness, bluntness, and the related wall shear stress.; For a small angle between the daughter-vessel axis and the parent-vessel axis, i.e., a small turning angle, the flow-field pattern in the entrance region of the daughter-vessel resembled that associated with an entrance region in a straight tube. However, with an increase in turning angle, the flow-field became dramatically altered. The velocity profile was highly skewed in the direction of the flow-divider wall with a transient velocity reversal near the wall opposite to the flow-divider. In addition, "M-shaped" velocity profiles were observed in the plane perpendicular to the plane of bifurcation. The distribution of wall shear stress around the circumference became nonuniform with increased values on the flow-divider wall and decreased values on the opposite wall. An increase in the Reynolds number enhanced the dependence of the local detailed flow characteristics on turning angle. For a large turning angle, the flow-field was significantly altered when a different flow-division between the daughter-vessels was imposed. Thus, the turning angle was found to dominate the detailed fluid-dynamic characteristics in the entrance region of the daughter-vessel and to overshadow the effects associated with other geometrical characteristics. The present findings suggest that the vulnerability of various arterial sites to the early development of atherosclerosis may be enhanced by the influence of unusual geometrical features on local fluid-dynamic characteristics. |
