Fluid/structure interaction for the flow in the left heart ventricle coupled with natural and prosthetic mitral valves


Monday, 10 April, 2017 - 15:00

Speaker: Valentina Meschini, GSSI-Gran Sasso Science Instutute

Room: A-133, SISSA Campus, Via Bonomea 265, Trieste

Abstract: The human heart is made of two separate volumetric pumps, the right and the left, the latter being the strongest since it feeds the systemic circulation that brings oxygenated blood to the whole body. Accordingly, the left part has to withstand the largest pressure differences that are in the range 1.6-2.1 x 10^4 Pa (120-160 mmHg). As a consequence, the aortic and mitral valves, that ensure the correct flow direction and prevent blood regurgitation from the aorta to the ventricle and from the ventricle to the atrium, respectively, are the most subjected to damage and impairing. Although several surgical procedures are available to repair and remodel the natural valves, in some cases their replacement is unavoidable and chosing the optimal prosthesis is crucial. Worldwide 280000 valve replacements are performed each year and this number is constantly increasing with a projection of about 800000 by 2050 owing to the increasing age of the population and a growing percentage of it accessing advanced medical care. Aortic and mitral valve replacement are almost equally distributed. However, while the former has already been the topic of extensive medical and scientific research, the latter has been less explored and its post-operative effects on the left ventricle dynamics still need to be analysed in details. In this paper the structure and 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, with fluid/structure interaction for the ventricle and mitral valve dynamics. The solver is preliminarily validated by comparisons with ad hoc experiments and then used for production runs. It is found that the left ventricular flow is heavily affected by the specific type of the mitral valve and the effects are more pronounced for ventricles with reduced pumping efficiency. More in details, when the ejection fraction of the ventricle (ratio of the ejected fluid volume and maximum ventricle volume over the cycle) is within the physiological range (EF = 50-70%), regardless of the mitral valve geometry, the mitral jet sweeps the inner ventricle surface up to the apex thus preventing the undesired flow stagnation. In contrast, for pathological ejection fractions (40%) the flow disturbances introduced by the prosthetic devices reduce the penetration capability of the mitral jet and weaken the recirculation in the ventricular apex. This is especially true for the bileaflet mechanical valve, whose disturbances on the mitral flow are the strongest and a region of stagnant fluid is produced. These findings have important clinical implications on the choice of the prosthetic devices in patients that need mitral valve replacement.