Vortex dynamics in healthy and pro-atherogenic carotid artery bifurcation models

Carotid artery atherosclerosis is a significant contributor to mortality in the United States. While it is recognized that low wall-shear stresses trigger plaque formation, there is a limited comprehension of the internal vortical structures that impact these stresses and how they differ between a healthy and a disease-prone, high-risk patient cohort. Our objective is to determine which driving factors, such as anatomical features (artery geometry) and mass-flow split, govern vortex behavior. Physiological pulsatile flow computational fluid dynamics simulations were performed on a “healthy” and a “disease-prone” carotid artery bifurcation model. Geometry and flow effects are investigated separately by simulating a third hybrid model having a healthy geometry with outlet boundary conditions imposing disease-prone flow conditions. This “unhealthy $\mathrm{\Delta }\mathrm{P}$” model recreated disease-prone mass-flow split and internal carotid artery sinus axial pressure gradient conditions in a healthy carotid artery bifurcation geometry. The results of our study revealed that the main vortex's time of formation is primarily dictated by carotid artery bifurcation geometry, whereas its lifespan is determined by the flow conditions. The main vortex's spatial expansion, as well as its circulation decay rate, are dictated by the geometry, not the flow conditions. We conclude that a high internal carotid artery mass flow rate and a higher favorable pressure gradient maximum magnitude occurring near peak systole are strong indicators of a high predisposition towards atherogenesis.