UBC Theses and Dissertations
Biomechanical modeling and hemorheological assessment of ascending thoracic aortic aneurysm, aortic heart valve, and blood clot Yeh, Han Hung
Cardiovascular diseases account for the most cause of death over the globe annually, summarized by the World Health Organization. An aortic aneurysm is one of the cardiovascular diseases with localized abnormal growth of a blood vessel with the primary risk of aneurysm rupture or aortic dissection. The precise pathological pathway for disease progression in aneurysm formation is not completely understood; however, biomechanically, disrupted blood flow from a diseased heart valve and thrombus formation potential in the dissection could contribute to the increased risk. The current ascending thoracic aortic aneurysm (ATAA) management rely heavily on ATAA diameter and blood pressure rather than biomechanical and hemodynamical parameters including arterial wall deformation or wall shear stress (WSS). Therefore, this thesis firstly evaluated the biomechanical contributions to ATAA progression under the influence of anatomy, hypertension, and hematocrit using fully coupled fluid-structure interaction (FSI) with arterial wall anisotropy to provide additional information in patient evaluations. The investigation was then extended to study the effect of blood rheology on the hemodynamics of a bileaflet mechanical heart valve with particle image velocimetry (PIV) validation. Finally, the rheological experimentations were conducted to analyze the coagulation process and the interactions between heparinized blood and the anticoagulation reversal agents. The ATAA analysis showed significant variations in the maximum WSS despite minimal differences in flow velocity between normotension and hypertension. The three different ATAA models identified different aortic expansions that were not uniform under pulsatile pressure and a geometry depended on elevated wall stress under hypertension. The investigation on the heart valve revealed the hematocrit influenced the shear stress distributions over a cardiac cycle. The structural stresses in the mechanical valve were affected by the shear stress distributions in the blood flow. Parameter dependencies study indicated that the hematocrit is influential when conducting patient-specific modeling of prosthetic heart valves. Finally, the use of small amplitude oscillatory shear (SAOS) rheometry for studying blood coagulation provided a comprehensive assessment with the combination of multiple rheological parameters for untreated and heparin neutralized blood. The coagulation characterization could be used towards the existing FSI models to account for potential blood clot formations in future studies.
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