SCHOOL OF MECHANICAL ENGINEERING SEMINAR Monday, December 3, 2012 at 15:00 Wolfson Building of Mechanical Engineering, Room 206

Ph.D Student of Prof. Moshe Rosenfeld, Prof. Rami Haj-Ali and Prof. Ehud Raanani

School of Mechanical Engineering, Tel-Aviv University

The aortic valve is located between the left ventricle and the aorta, allowing the oxygenated blood to flow into the aorta but preventing its backflow to the ventricle. Two distinctive disorders are related to the aortic valve, aortic stenosis and aortic regurgitation. These disorders can be caused, for example, by congenital diseases and aortic root aneurysm, respectively. The present talk will introduce a new fluid-structure interaction (FSI) model of native aortic valves and its implementation for investigating the tissue mechanics and hemodynamics in different morphologies, pathologies and clinical interventions.

The numerical model includes valve coaptation under physiologically realistic boundary conditions and tissue properties. The FSI simulations are based on fully coupled structural and fluid dynamic solvers that facilitate accurate modeling of the pressure load on both the root and the cusps. The partitioned solver has non-conformal meshes and the flow is modeled employing the Eulerian approach. The cusps' tissues in the structural model have hyperelastic behavior and different layers of elements for the collagen fibers network and the elastin matrix. Tissue behavior of the aortic sinuses is also hyperelastic. The coaptation is modeled with a master-slave contact algorithm. The opening, systole, closing and diastole phases are simulated by imposing physiological blood pressure at the ventricle and aortic boundaries.

This FSI model was employed in several parametric studies of aortic root geometries. The aim of these studies was to optimize the kinematic and mechanical performance of aortic valves post valve-sparing procedure, in which the aneurysmatic root is replaced while retaining the native valve. These parametric studies suggest that decreased aortic annulus diameter increases coaptation and lead to better valve performance. Improving effective height during valve repair or replacement, by either aortic annulus or cusp intervention, could lead to increased diastolic coaptation and better performance, especially for non-prolapsed valve geometries. The best combination of large coaptation, low stress in the tissues during diastole and low flow shear stress during systole were found in cases with identical annulus and sinotubular diameters, and therefore valve-sparing procedures with annuloplasty that prevent annulus expansion are preferable.

The model was also employed to investigate asymmetric bicuspid aortic valve (BAV), which is a congenital cardiac disorder where the valve consists of only two cusps instead of three as in a normal valve. It was found that BAVs have significantly smaller opening areas and larger stress values at both systole and the diastole. The asymmetric geometry caused asymmetric vortices and much larger wall shear stress on the cusps, which could be a potential cause for early valvular calcification in the BAVs.

Fluid-Structure Interaction Model of Native Aortic Valves

Gil Marom