CFD Simulation of a Novel Bileaflet Mechanical Heart Valve Prosthesis - An Estimation of the Venturi Passage Formed by the Leaflets

Abstract

The aim of this study was to validate the flow characteristics of the novel Helmholtz-Institute Aachen Bileaflet (HIA-BL) heart valve prosthesis. The curved leaflets of the HIA-BL valve form a Venturi passage between the leaflets at peak systole. By narrowing the cross section the flow accelerates and the static pressure at the central passage decreases according to the Venturi effect. The low-pressure zone between the leaflets is expected to stabilize the leaflets in fully open position at peak systole. To investigate the Venturi passage, the flow fields of two valve geometries were investigated by CFD (Computational Fluid Dynamics): one geometry exhibits curved leaflets resulting in a Venturi passage; the other geometry features straight leaflets. The flow profiles, pressure distribution and resulting torque of both passages were compared and investigated. Although flow profiles downstream of both valves were similar, the flow passages between the leaflets were different for the investigated leaflet geometries. The straight leaflet passage showed a large boundary layer separation zone near the leaflets and the lowest pressure at the leading edge of the leaflet. The Venturi passage showed a reduction of the boundary layer separation zones and the lowest pressure between the leaflets could be found in the narrowest flow cross section of the Venturi passage. Additionally, the resulting torque showed that the Venturi passage produced an opening momentum. The results demonstrate that the Venturi passage stabilizes the leaflets in open position at peak systole.

Direct numerical simulation of the pulsatile flow through an aortic bileaflet mechanical heart valve

“…In other studies, only part of the cycle is considered (Myers & Porter 2003) and the numerical simulation imposes symmetries (Cheng, Lai & Chandran 2004) so as to decrease the computational cost. In addition, in the majority of the literature, turbulence models are used to avoid the explicit simulation of the smallest scales (Grigioni et al 2005;Yokoyama et al 2006;Alemu & Bluestein 2007, among many others); this substantially reduces the nodes of the mesh and allows for larger integration time steps, but at the expense of the information on the turbulence fine scales whose accurate description is mandatory for the comprehension of the clinical phenomena mentioned above. Recently, Borazjani et al (2007) and Borazjani, Ge & Sotiropulos (2008) considered the full three-dimensional flow dynamics in an axisymmetric aortic root, including fluid-structure interactions.…”

Numerical simulation of the dynamics of a bileaflet prosthetic heart valve using a fluid–structure interaction approach

“…In this research framework, Grigioni et al (2005a) performed a numerical simulation on a model of mechanical valve placed in a physiological aortic root shaped model, furnishing indications about the role of Valsava sinus on the fluid dynamic downstream of the valve at mid systole. Yokoyama et al (2006) demonstrated that curved leaflet configuration generates a Venturi effect that is able to reduce the boundary layer separation zones and stabilize the leaflets' position. Ge et al (2003) provided an insight into the complex hemodynamics of a bileaflet MHV at the maximum Reynolds number, putting in evidence that high grid densities are mandatory, in order to fully characterize local aspects of the flow field downstream of the prosthetic valve.…”

MRI: a tool for measuring turbulent intensities in flow systems

“…This region is distinct as far as 2 diameters from the valve but shows a much smaller fluid speed than the principal flow. Some fluid speeds were zero velocities and some were of negative values as seen in figure [5]. The negative velocities oppose the flow direction, some of which appeared upstream of the valve.…”

“…At the opened leaflet, the fluid jet carries turbulent velocity fluctuations further downstream than in configuration I. The region of lower counter flow velocities which is in-between the high turbulent diffusivities that resulted from jet velocities is bounded by regions of high shear [5]. This recirculation phenomenon has been known to have a physiological impact.…”

“…The first prosthetic heart valve implant of this valve was preformed in 1960, and ever since, attention has been drawn to the study of flow dynamics past such valves and to the investigation of related physiological complications. Among the methods used to study are pulse Doppler ultrasound, laser Doppler anemometry, hot wire-film anemometry, and numerical methods such as computational fluid dynamics [CFD] [3,5]. Recently, particle image velocimetry (PIV) [6] and particle tracking velocimetry [7] were used in in vitro studies of flow dynamics downstream of prosthetic valves.…”