This study presents numerical simulations of a minimally constrained mechanical valve model using a fully coupled fluid-structure interaction method with COMSOL Multiphysics, a finite-element-based software package. The model applies a physiological pulsatile pressure gradient across an aortic valve with an approximately symmetric aortic root. The complex hinge from the exact model is simplified with a pin joint and weak constraints to control the designated valve leaflet positions. The arbitrary Lagrangian-Eulerian method is applied in order to accommodate large mesh displacements due to leaflet motion. Constant material properties are applied to both the fluid and structure with the assumption that the flow is Newtonian and turbulent. The valve leaflet positions and flow patterns are verified against the results from literature. Hemodynamic performance in terms of flow velocity and shear stress is investigated. The maximum von Mises stress for each valve leaflet is calculated. Moreover, a simulation on a defective mechanical valve is conducted and hemodynamic and structural analyses are performed. It is found that vortices were generated with higher blood velocity passing through the unconstrained leaflet, which may lead to diagnostic confusion.

Cardiovascular disease has historically been the leading cause of death in the US [1], and accounts for approximately one third of all deaths worldwide [2]. Coronary artery disease in particular accounts for over fifty percent of these deaths and in 2004 was the single largest killer, affecting approximately 15 million people every year [1]. Coronary stenting was approved in 1994 by the FDA, and has become one of the leading treatments for the disease. However, problems persist in both bare metal and drug-eluting stents (DESs) with restenosis and thrombosis. It is well accepted that disruptions in arterial wall shear stress (WSS), especially low WSS, are linked to alterations in the endothelial cell layer and ultimately disease [3], although the exact mechanisms are still uncertain. Additionally, studies have shown that stent design is closely linked to clinical outcomes [4].

Cardiovascular disease has historically been the leading cause of death in the US [1], and coronary artery disease in particular accounts for over fifty percent of these deaths [1]. Since their approval in 1994, coronary stents have become one of the leading treatments for this disease. However, problems persist in both bare metal and drug-eluting stents (DESs) with long-term restenosis and thrombosis. It is well accepted that disruptions in arterial wall shear stress (WSS), especially low WSS, are linked to alterations in the endothelial cell layer, atherosclerosis, and thrombogenesis [2], although the exact mechanisms are still uncertain, and studies have shown that stent design is closely linked to clinical outcomes [3].

In this paper, performance of aortic heart valve prosthesis in different geometries of the aortic root is investigated experimentally. The objective of this investigation is to establish a set of parameters, which are associated with abnormal flow patterns due to the flow through a prosthetic heart valve implanted to the patients that had certain types of valve diseases prior to the valve replacement. Specific valve diseases, classified into two clinical categories, were correlated with the corresponding changes of aortic root geometry. These categories correspond to aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. Experiments were performed at test conditions corresponding to 70 beats/min, 5.5 L/min target cardiac output and a mean aortic pressure of 100 mmHg. By varying the aortic root geometry, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.

Qualitative and quantitative flow visualization study was conducted for the case of a biomimetic pulsatile flow through an artificial heart valve placed into an asymmetric model of an aortic root with sinuses of Valsalva. A prototype trileaflet valve was tested alongside with a tilted disk valve and a bileaflet valve. The study was conducted in test conditions corresponding to 70 beats/min, 5.5 l/min target cardiac output and a mean aortic pressure of 100 mmHg. Flow visualization data obtained using digital particle image velocimetry (PIV) was phase-averaged in order to provide accurate, time-resolved patterns of flow velocity and viscous shear stress values. In the case of the tri-leaflet valve, during systole, a stable jet emanates from the valve, with vortical structures forming on the sides of the jet. These vortical structures entrain the surrounding fluid into the jet, which leads to development of a shear flow instability downstream of the valve. For all considered valve types, a recirculating flow was observed in the sinus area during both the systole and the diastole. No indication of a stagnating flow region was observed, as the fluid was completely washed out from the aortic sinus within each cardiac cycle.