Optimizing of the design of a prosthetic heart valve with three leaves

MARIO ROBERTO ROSENBERGER; AMERIO, O. N.; SCHVEZOV, C. E.

Argentina. http://www.fac.org.ar/ccvc

Congreso; IV Congreso Virtual de Cardiologia,; 2005

Federación Argentina de Cardiologia

The interest in developing a prosthetic heart tri-laeflet valve is based on the durability of mechanical prosthesis; the good hemodynamic performance of bio-prosthesis due to the central flow, its perfect closure, the negligible thrombogenic index, and the negligible perception of its presence by the user. Objectives Develop a mathematical model of a fourth generation prosthetic heart valve or tri-leaflet valve. Obtain an optimal design through numerical modeling using computational fluid dynamics. Modeling procedure Two mathematical models based in 3-D computational fluid dynamics were developed; one of a tri-leaflet valve and another of a typical flat bi-leaflet valve with a maximum aperture of 85º. In both cases the models were axis-symmetric following the real physical symmetry. This assumption permitted to take into account in the model, only a sixth and a fourth of the cylindrical section for the tri- and bi-leaflet valves respectively. In such way the number of elements and calculation efforts were significantly reduced. The blood was assumed to be a Newtonian fluid and incompressible, isothermal and in a steady state of flow. For solving the reduced Navier-Stokes equations a finite element method was used and the domain was discretized using isoparametric hexahedric elements. Figure 1.a shows a schematic array of the tri-leaflet valve model and figure 1.c indicates the sixth-part of the valve, which was actually modeled. In the figure it is observed that the valve was located in a cylindrical tube with rigid walls. This configuration permitted to analyze the flow in any perpendicular section before and after the blood passes the valve [1, 2]. The blood as a fluid was characterized employing the typical Reynolds number (Re), which was calculated as it is shown in Table I. The physical parameters used to simulate the blood flow were the viscosity, density, flow rate which were assigned to have the following values 0.004 Pa.s, 1.050g/cm3 and 5,000 cm3/min respectively, these values are the average flow for an adult under normal conditions. The internal diameter of the tube was 27 mm [3, 4]. For these values the corresponding Re has a value of 1031. In order to analyze the valve behavior, the models were run for Re in the range of 100 to 2000. The discretization of the model domain was done using Gambit 1.2(R). The finite element models were developed using Fidap 8.5(R). The model results were mathematically validated comparing the results obtained with the present model for the bi-leaflet valve and those reported in the literature for the same valve. [1, 2] Results The results show two very different flow patterns between the bi- and tri-leaflet valves. Both flows can be observed in figures 3 and 4 for the bi- and tri-leaflet valves respectively. The opening for the bi-leaflet valve is 85º and for the tri-leaflet valve is 65º. In both cases the flow patterns correspond to cross sections at 2 mm from the valve plates. In both cases the Re number is 1000. The main characteristic of each flow are as follows. In the case of the bi-leaflet valve the flow occurs mainly through two parallel and lateral channels (79.3%) with a narrow central section responsible of 20.7% of the flow. The flow has a perfect two-folds symmetry, as expected. In the case of the tri-leaflet valve shown in figure 4 it is observed that the flow occurs through three symmetric areas near the valve periphery which are located between each leaflet and the valve ring. The central flow has a three-fold symmetry and occupies a wide area of the valve. In addition, it is...