Flow structure in healthy and pathological left ventricles with natural and prosthetic mitral valves

Abstract

In this paper, the structure and the dynamics of the flow in the left heart ventricle are studied for different pumping efficiencies and mitral valve types (natural, biological and mechanical prosthetic). The problem is investigated by direct numerical simulation of the Navier-Stokes equations, two-way coupled with a structural solver for the ventricle and mitral valve dynamics. The whole solver is preliminarily validated by comparisons with ad hoc experiments. It is found that the system works in a highly synergistic way and the left ventricular flow is heavily affected by the specific type of mitral valve, with effects that are more pronounced for ventricles with reduced pumping efficiency. When the ventricle ejection fraction (ratio of the ejected fluid volume to maximum ventricle volume over the cycle) is within the physiological range (50 %-70 %), regardless of the mitral valve geometry, the mitral jet sweeps the inner ventricle surface up to the apex, thus preventing undesired flow stagnation. In contrast, for pathological ejection fractions ( 40 %), the flow disturbances introduced by the bileaflet mechanical valve reduce the penetration capability of the mitral jet and weaken the recirculation in the ventricular apex. Although in clinical practice the fatality rates in the five-year follow-ups for mechanical and biological mitral valve replacements are essentially the same, a breakdown of the deaths shows that the causes are very different for the two classes of prostheses and the present findings are consistent with the clinical data. This might have important clinical implications for the choice of prosthetic device in patients needing mitral valve replacement.

A consistent approach for fluid‐structure‐contact interaction based on a porous flow model for rough surface contact

“…Condition (26) guarantees that there is always a positive gap or no gap between potentially contacting bodies. Additionally, (27) restricts the minimal stress by compression transferred directly between the solid bodies to the surrounding fluid normal traction.…”

“…Therefore, fluid equations, such as the Navier-Stokes equations, are considered spatially resolved without including information concerning the fluid domain or boundary/ interface conditions beforehand and are coupled to the structural deformation. Details on such methods can be found, eg, in other works, [13][14][15] and in related works [16][17][18][19][20][21][22][23][24][25][26] which include attempts to treat contact of submersed bodies. However, none of these methods are able to meet the challenges concerning contact mentioned above with respect to physical modeling and practicability of the numerical approach.…”

A numerical study of hemodynamic effects on the bileaflet mechanical heart valve

“…During severely pathological states of the valves, such as aortal stenosis or mitral regurgitation, their replacement with artificial implants may be unavoidable. With the current trend of population aging, it is estimated that the current number of 280 000 heart valve transplantations per year will triple over the next 30-year period [1]. It can also be assumed that the requirements for the lifetime span of the artificial valves will further increase.…”

“…The cardiac cycle represents a vastly complex process in terms of both experimental measurement and CFD modeling. A pulsatile flow changes from laminar to turbulent state, although a fully turbulent whirl cascade cannot be developed in such a short time [1]. Rotation of the valve leaflets and the movement of the surrounding domain responds to blood flow, muscle contractions and wall elasticity.…”

“…As the comparatively realistic CFD modeling requires quite complex numerical model as well as extensive computational resources, the introduction of some model simplifications is generally desired. Specifying the leaflet movement in order to simplify the interaction model between the fluid and solid phases was found inappropriate due to the formation of additional vortex structures [1,9]. Despite the distinctly lower computational costs, the two-dimensional solution must be used with consideration that some vortex structures can not develop due to a symmetry condition [10,11].…”