An Uncoupled Multi-Scale CFD Approach to Cell Motion in the Human Left Coronary Artery: Relation to Plaque Progression

The near wall motion and residence time of cells that participate in atherosclerosis is an important factor in the development and progression of atherosclerotic lesions. Attachment of leukocytes and monocytes depends upon a complex biological milieu, including expression of adhesion molecules and receptors at cell surfaces, but biomechanical forces also come into play in the local microenvironment. Cell attachment to the endothelium begins with rolling at the surface and can consummate in firm adhesion. These phenomena are influenced by flow-induced forces and moments acting on the cell in proximity to the endothelium. The initial rolling condition and capture process are related to the local shear flow, and there have been extensive investigations — both theoretical and experimental — of these phenomena for various cell types [1–3]. In most studies, steady flow and analytical methods based on Stokes equations were widely used, since the Reynolds numbers are extremely low. In our study, we focus on relating simulated cell motion to conditions in the region of an atherosclerotic plaque in an effort to assist in the interpretation of concurrent investigations of plaque development and progression in human coronary arteries. Thus, our studies are not designed to address fundamental questions of the biology of cell attachment but rather are aimed at elucidation of clinical observations. An inherent challenge is the fact that the length scales of interest vary from sub-micron to millimeters, a range ∼ 10⁴–10⁵ that presents a significant computational task if tackled directly. Hence, various schemes have been employed to address this multi-scale computational problem. Our approach here is intended to decouple the macro (∼ sub-mm) and micro (∼ sub-μm) flows in an effort to achieve computational simplicity, yet preserve accuracy, and thus to concentrate on relevance to flow in the human coronary arteries.