A BIOMIMETIC APPROACH FOR THE RESTORATION OF THE PHYSIOLOGICAL LEFT VENTRICULAR VORTEX FORMATION

Abstract

In a human heart, a large asymmetric clockwise vortex in the left ventricle smoothly redirect incoming blood from the mitral annulus to the aorta with minimal energy loss during ventricular diastole. However, implantation of artificial valves at the mitral position results in the loss of this physiological vortical formation, leading to an overall unstable flow in the left ventricle. This study seeks to: (I) Investigate the possibility of restoring the physiological left ventricular vortex formation by applying biomimicry to a tissue valve design, (II) design and develop a biomimetic mechanical mitral valve with improved hemodynamic performance, (III) investigate the effect of the anterior leaflet on vortex formation, (IV) investigate the effects of orifice geometry and position on left ventricular vortex formation and turbulence intensity.

Two-dimensional particle Image Velocimetry technique was employed to capture the left ventricular downstream flow field of a novel tissue bioprosthesis installed within a mock left heart circulatory loop that mimicked the physiological environment in the left ventricle. The results were then compared to that of the well-established St. Jude Epic valve which functioned as a control in the study. Although both valves were found to have similar Reynolds shear stress and Turbulent Kinetic Energy levels, the novel D-shape valve was found to have lower turbulence intensity and greater mean kinetic energy conservation.

In addition, a bi-leaflet mechanical heart valve design (Bio-MHV) that mimics the geometry of a human mitral valve was also designed and fabricated, with the aim of reducing turbulence levels in the left ventricle by replicating physiological flow patterns. An in vitro three-dimensional particle velocimetry imaging experiment was carried out to compare the hemodynamic performance of the Bio-MHV with that of the clinically established ATS valve. The Bio-MHV was found to replicate physiological left ventricular flow patterns and produced relatively lower turbulence levels.

Furthermore, in vitro experiments involving 2D3C particle image velocimetry was subsequently done on a newly designed mechanical valve consisting solely of a curved anterior leaflet and the results compared against that of the well-established Hancock II tissue bio-prosthesis, with the latter functioning as a control. The findings obtained suggest that hemodynamic performance can be improved by solely mimicking the geometric feature of the anterior leaflet in a mechanical valve design, potentially resulting in lower thrombosis.

Finally, the effect of orifice geometry and its position with respect to the posterior wall of the ventricle on vortical formation and turbulence intensity in the left ventricle, by utilizing four separate orifice configurations within an in vitro left heart simulator. Stereo particle image velocimetry experiments were then carried out to characterize the downstream flow field of each configuration. The findings obtained demonstrate that the generation of the physiological left ventricular vortical flow was not solely dependent upon the orifice shape but rather the subsequent jet-wall interaction of which the distance of the orifice geometric center from the left ventricular posterior wall plays a significant role. In conclusion, the findings of this dissertation can be the foundation upon which future biomimetic mitral valve designs are derived.