Análise numérica fluido-estrutural do fenômeno de flutter em próteses de válvulas cardíacas biológicas

Abstract

The low lifetime of biological prosthetic valves, comprising 10-15 years, is closely related to the occurrence of oscillations of the valve cusps due to interaction with blood flow, a phenomenon known as flutter. Furthermore, studies indicate that the parameters of leaflet oscillations are related to the geometry of heart valve prostheses. In this scenario, the objective of the present work is to perform a numerical fluid-structural study to evaluate the behavior of the flutter phenomenon of the leaflets of biological aortic valve prostheses. For this purpose, the biological prosthesis geometry, based on a geometric model available in the literature, and a fluid computational domain composed of an inlet region, outlet region and the sinuses of Valsalva were developed. The cusps thickness and the protrusion height of the valves were changed to analyze the influence of the geometric parameters of the valves on the vibrational parameters of the flutter. As boundary condition, a parabolic velocity profile was applied at the inlet, outflow at the outlet and fixed support on the sides of the leaflets. The valve cusps were considered to have linear elastic and isotropic behavior, while the blood was modeled as a Newtonian fluid. Turbulence was modeled according to the k – ω SST model. The simulations were performed using the commercial software Ansys 2023 R1. The numerical results indicated that, due to the occurrence of leaflet oscillations, both fluid dynamic quantities, such as pressure, velocity and turbulence intensity, as well as solid domain quantities, such as stress and strain, presented an irregular and oscillatory behavior. Furthermore, the radial displacements of the leaflets were asynchronous, and the phase difference between the leaflets increased with the increase in the thickness of these bodies. The blood flow at valves downstream was also impacted by the vibrational movement of the leaflets, having a wave-like behavior and with peaks of velocities and turbulence intensities coinciding with the moments of the troughs of the leaflet movement. Finally, the frequencies ranged from 28.3 Hz to 36.7 Hz, while the amplitudes ranged from 5.34 mm to 6.53 mm, where the valve with the lowest protrusion height did not develop flutter throughout the period that the valve is open.