Simulating blood flow and oxygen transport in stenosed large arteries

Altered flow and mass transfer patterns are thought to play an important role in the early onset of atherosclerosis. A disturbed wall shear distribution and the prevalence of hypoxic (low oxygen tension) are specifically believed to be atherogenic factors, which can function as a positive feedback on the development of atherosclerosis. In this work, blood flow and oxygen mass transport have been modelled in stenosed arteries and numerically evaluated, to better understand the atherogenic processes that contribute to this development. Three stenosed geometries have been considered: one with light (31% asymmetric area reduction) stenosis and two with moderate stenosis (56% area reductions, one of which asymmetric, another axisymmetric). Two different rheological models have been created for blood. In the first, blood is assumed to be Newtonian; in the latter, the Carreau-Yasuda model is considered to account for the shear thinning effect of blood and to reproduce a more physiologically accurate rheological model, after which the two models have been compared. The simulations mimicked the flow conditions in large arteries, with Re = 300 and using the velocity profile of the internal carotid artery for transient simulation runs. Results show that wall shear stress (WSS) and Sherwood profiles are highly dependent on stenosis geometry, although certain characteristics are found for all stenoses. First, a region of increased wall shear stress can be found proximal to the stenosis throat, usually followed by a low shear region distal to the stenosis throat. Wall shear stress magnitudes can reach 10 to 20 times the Poiseuille value depending on the geometry and the length of the stenosis. Second, the Sherwood profile in stenosed arteries follow the same characteristics, although asymmetric stenoses can lead to more complex patterns at both the diseased and healthy wall of a stenosed artery. One particular asymmetric stenosis geometry caused significant hypoxic regions just distal and distolateral to the stenosis throat, with Sherwood numbers as low as Sh = 1.37. This might indicate that oxygen transport to the wall is fluid phase-limited in these aforementioned regions. The lowered oxygen transport through the artery wall can lead to a change in wall permeability which has been linked to an early onset of atherosclerosis.