published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Hemodynamic factors play a role in atherogenesis and the localization of atherosclerotic plaques. The human aorta and coronary arteries are susceptible to arterial disease, and there have been many studies of flows in models of these vessels. However, previous work has been limited in that investigations have not modeled both the geometry and flow conditions in specific individuals. The first aim of the research was to develop a methodology that combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) to simulate the blood flow patterns found in the human aorta. The methodology included MR image processing, 3D model reconstruction and flow simulation using in vivo velocity boundary conditions obtained from phase contrast (PC)-MRI scanning. The CFD simulations successfully reproduce the unusual right-hand helical flow pattern that has been reported in the ascending aorta, giving confidence in the accuracy of the methodology. The second aim was to investigate the causes of the right-hand helical flow. It was found that the correct flow dynamics could only be produced by including the specific aortic motion caused by the beating heart; and it is concluded that this is a significant factor in producing the observed in vivo helical flow patterns. The entrance flows of coronary arteries are expected to be affected by flow in the aortic root, and the third aim was to explore these effects using models that include aorta and coronary arteries. The simulation results demonstrate that a pair of axial vortexes with different rotating directions exists in the entrance segments of the right and left coronary arteries during systole and early diastole, producing asymmetrical wall shear stress (WSS) distributions. The last aim of the research was to examine possible relationships between WSS distributions induced by the entry flow patterns and the frequency distributions of atherosclerosis in the proximal segments of coronary arteries reported in the clinical literature. A close correspondence between low WSS and higher frequency of plaque occurrence was observed. The tools developed in this study provide a promising avenue for future study of cardiovascular disease because of the ability to investigate phenomena in individual human subjects.