According to the World Health Organization (WHO), Cardiovascular Disease (CVD) is the leading cause of death in the world. Biomechanics and fluid dynamics of blood flow play an important role in CVD mediation. Shear stress plays a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur. In this study, a three-dimensional dynamic model of platelet-rich thrombus growth in stenosed vessels using computational fluid dynamics (CFD) methods is introduced. Platelet adhesion, aggregation and activation kinetics are modeled by solving mass transport equations for blood components involved in thrombosis. The model was first verified under three different shear conditions and at two heparin levels. Three-dimensional simulations were then carried out to evaluate the performance of the model for severely damaged (stripped) aortas with mild and severe stenosis degrees. For these cases, linear shear-dependent functions were developed for platelet-surface and platelet-platelet adhesion rates. It was confirmed that the platelet adhesion rate is not only a function of Reynolds number (or wall shear rate) but also the stenosis severity of the vessel. General correlations for adhesion rates of platelets as functions of stenosis and Reynolds number were obtained based on these cases. The model was applied to different experimental systems and shown to agree well with measured platelet deposition. Then, the Arbitrary Lagrangian Eulerian (ALE) formulation was used to model dynamic growth by including geometry change in the simulation procedure. The wall boundaries were discretely moved based on the amount of platelet deposition that occurs on the vessel wall. To emulate the dynamic behavior of platelet adhesion kinetics during thrombus growth, the validated model for platelet adhesion, which calculates platelet-surface adhesion rates as a function of stenosis severity and Reynolds number, was applied to the model. The model successfully predicts the nonlinear growth of thrombi in the stenosed area. These simulations provide a useful guide to understand the effect of growing thrombus on platelet deposition rate, platelet activation kinetics and occurrence of thromboembolism (TE) in highly stenosed arteries. / Ph. D. / Continuous platelet deposition in coronary arteries creates a narrow necking area at some susceptible regions such as bifurcations, stented arteries and ruptured vessel walls. These narrow regions, known as stenoses, are the number one cause of heart attacks. In this work, a predictive model of platelet deposition (i.e. thrombosis) is developed based on previous experimental and clinical data on human blood. Fluid shear stresses play a major role in platelet-substrate interactions and thrombus formation and growth in blood flow, where under both pathological and physiological conditions platelet adhesion and accumulation occur.
In addition to simulating the blood flow patterns in arteries with computational fluid dynamics (CFD), the model is able to reliably predict the amount of platelets deposited in injured areas, the severity of the blockage in the blood flow, and the time for occlusion. The results of our model are much more accurate than previous models and are validated by comparing them to clinical data for thrombus formation in stenosed arteries. Thus, the project contributes towards better diagnosis and treatment of vascular disease with implications on the monitoring and management of cardiovascular diseases and providing useful guidelines to design improved devices such as left ventricular assist devices, mechanical heart valves, stents, etc.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/89325 |
| Date | 06 November 2017 |
| Creators | Hosseinzadegan, Hamid |
| Contributors | Mechanical Engineering, Tafti, Danesh K., Qiao, Rui, Staples, Anne E., Behkam, Bahareh, Chappell, John C., Grant, John Wallace |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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