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Description
The aortic heart valve is a delicate, complex structure that resides between the left ventricle and the aorta, enabling unidirectional flow of blood. Proper function of the valve allows unobstructed flow out of the heart, and prevention of retrograde flow into the heart (regurgitation). Congestive heart failure (CHF) is a term used to describe conditions that impair the heart's ability to provide adequate blood supply to the body. Conditions affecting the left ventricle or the aortic valve may fall into this category. A left ventricular assist device (LVAD) is sometimes prescribed to patients with CHF, to supplement the blood flow that can be provided by the heart. The LVAD is a device that mechanically pumps blood from the left ventricle to the aorta, bypassing the aortic valve. The LVAD decreases left ventricular pressure, which alters the pressure gradient across the aortic valve and causes the valve to remain closed for a longer duration, or possibly for the entire cardiac cycle. As a result, the valve leaflets my fuse to one another, and modified blood flow patterns in the region may cause hemostasis in the aortic root. By analyzing values of published data describing the dimensions of aortic valve parameters, a set of dimensions is established that describes the geometry of a typical adult valve in the closed position. These parameters include valve height, radius, and angles between features. A methodology is defined for creating 3D solid models of the aortic valve, using SolidWorks parametric design software. This methodology is used to create four models of the aortic valve, the first of which is a model comprised entirely of thin surfaces. To create the second model, additional thin surfaces are added to the valve to create aortic sinuses, an important anatomical feature of the aortic root. The third model is comprised of solids, with a solidified valve body and material thickness represented in the leaflet coaptation surfaces. The fourth model is comprised of solids as well, but has a hollow valve body and defined geometry on the proximal leaflet surfaces. Calculations are performed to evaluate the dimensions of various parameters of the valve geometry, using the defining dimensions as independent variables. Both the surface models and the solid models are successfully created, with defining parameters that can be modified based on input dimensions. The calculations are used to define valve geometry that describes two modified versions of the original valve. Additional solid models are created to reflect these modified dimensions. The modified versions have values of leaflet height at the center of the valve that are 30% and 170%, respectively, of the original leaflet height. Having created these three fully defined solid models, a physical prototype of each version is manufactured using fused deposition modeling (FDM) 3D printing technology. The physical prototypes of the original valve and two modified valves are intended for use with laboratory hardware for fluid flow analysis. Such research will provide insight into the value of prosthetic implants used to modify the topography of the aortic valve in LVAD patients, thus affecting blood flow patterns. As well, the 3D solid models and surface models may be used for a variety of computational analyses to predict fluid flow conditions and structural behavior of the valve. The models are also candidates for further geometric modification, by the addition of features to have them represent valves with either structural or acquired deficiencies.
