(316ae) Blood Flow Patterns in the Carotid Artery and the Risk of Atherosclerotic Diseases

Some of the most serious forms of cardiovascular diseases (like atherosclerosis, thrombosis, and stenosis) are caused by problems associated with the carotid artery. Atherosclerosis is the hardening of the arteries caused by the build-up of plaque. The build-up of plaque results in the narrowing of artery lumen, which can lead to heart attacks. Blood dynamics plays a very important role in atherosclerosis initiation and progression. It has been widely observed that atherosclerotic diseases occur at sites with complex hemodynamics, such as bifurcations, junctions, and regions of high curvatures. These regions usually have very low or highly oscillatory shear stress [1].

In the present work, pulsatile blood flows in arteries were simulated using a finite volume numerical method. The purpose was to predict individual hemodynamic flows in patients with typical carotid artery geometry, and develop diagnostic tools to quantify the risk for diseases.

The human carotid artery consists of the common carotid that bifurcates into the external and the internal carotid arteries. A sinus is usually present in the internal carotid artery, right after the bifurcation. In the present study, the bifurcation angle is defined to be the angle between the external and the internal carotid, and the off-plane angle is the angle of the internal carotid with the plane of the common and the external carotids. In order to study the effects of carotid geometry on the blood flow pattern, the bifurcation angles investigated were varied from 10o to 30o and the off-plane angles from 0o to 15o. Blood flow was simulated with the software package Fluent using second-order unsteady solver with laminar viscous model. The pulsating inlet flow rate of the common carotid artery was based on experimental measurements using Magnetic Resonance Imaging (MRI) by Marshall et al. [2]. This function was used to generate the inflow boundary condition in the simulations. The volumetric flow rates through the external and internal carotids were calculated as a function of time, and were found to agree quite well with the measurements of Marshall et al. [2]. The wall shear stress (WSS) and the velocity profile can also be calculated at any location and time. For all bifurcation angles investigated, the regions with WSS below 0.5 Pa, the level below which an atherogenic phenotype is believed to be stimulated, was found to occur at the sinus. Highest WSS (10 Pa or higher) was found to occur at the apex. The velocity gradients near the sinus wall were seen to fluctuate, and reverse flows near the sinus wall occurred at times. The paper will also discuss the risk of having plaque build-up for different carotid geometries as a function of the carotid bifurcation geometry. This will include the calculations of the fraction of time at which the sinus WSS stays below the critical values of 0.5 Pa and the fraction of time at which reverse flows occur near the sinus wall for different bifurcation angles, off-plane angles, and sinus sizes.

References:

[1] H. F. Younis, M. R. Kaazempur-Mofrad, R.C. Chan, A. G. Isasi, D. P. Hinton, A. H. Chau, L. A. Kim, R. D. Kamm, “Hemodynamics and wall mechanics in human carotid bifurcation and its consequences for atherogenesis: investigation of tinter-individual variation” Biomechan. Model Mechanobiol., 3, 17-32, 2004.

[2] I. Marshall, P. Papathnasopoulou, K. Wartolowska., “Carotid flow rates and flow division at the bifurcation in healthy volunteers,” Institute of Physics Publishing, 25, 691-697, 2004.