Role of vortices in cavitation formation in the flow across a mechanical heart valve.

Background And Aim Of The Study: Cavitation occurs during mechanical heart valve closure when the local pressure drops below vapor pressure. The formation of stable gas bubbles may result in gaseous emboli, and secondarily cause transient ischemic attacks or strokes. It is noted that instantaneous valve closure, occluder rebound and high-speed leakage flow generate vortices that promote low-pressure regions in favor of stable bubble formation; however, to date no studies have been conducted for the quantitative measurement and analysis of these vortices.

Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.

Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood.

Squeeze flow measurements in mechanical heart valves.

High-speed squeeze flow during mechanical valve closure is often thought to cause cavitation, either between the leaflet tip and flat contact area in the valve housing, seating lip, or strut flat seat stop, depending on design. These sites have been difficult to measure within the housing, limiting earlier research to study of squeeze flow outside the housing or with computational fluid dynamics. We directly measured squeeze flow velocity with laser Doppler velocimetry at its site of occurrence within the St.

Shear stress investigation across mechanical heart valve.

The particle image velocimetry technique was used to study the shear field across a transparent mechanical heart valve model in one cardiac cycle. Shear stress was continuously increased until peak systole and high turbulent stress was observed at the orifice of the central channel and also around the occluder trailing tips. The peak Reynolds shear stress was up to 500 N/m at peak systole, which was higher than the normal threshold for hemolysis.

The effect of tip angle on cavitation potential during closure of a bileaflet prosthesis model.

Background And Aim Of The Study: Mechanical heart valve (MHV) cavitation has been widely investigated by negative pressure transient (NPT) measurements. Whilst NPT is believed to be the cause of cavitation as the valve occluder approaches its fully closed position, some valves are also more prone to cavitation initiation. The study aim was to determine the effect of tip angle on the occluder trailing edge for the MHV closure flow field and cavitation potential.

Particle image velocimetry study of pulsatile flow in bi-leaflet mechanical heart valves with image compensation method.

Particle Image Velocimetry (PIV) is an important technique in studying blood flow in heart valves. Previous PIV studies of flow around prosthetic heart valves had different research concentrations, and thus never provided the physical flow field pictures in a complete heart cycle, which compromised their pertinence for a better understanding of the valvular mechanism. In this study, a digital PIV (DPIV) investigation was carried out with improved accuracy, to analyse the pulsatile flow field around the bi-leaflet mechanical heart valve (MHV) in a complete heart cycle.

Leukocyte-endothelium interaction: measurement by laser tweezers force spectroscopy.

Leukocyte adhesion to vascular endothelium is an initial step of many inflammatory diseases. Although the atomic force microscopy (AFM) measurements of leukocyte-endothelial interaction have been recently introduced. with cell adhesion force unbinding curves (CAFUC).

An experimental study of steady flow patterns of a new trileaflet mechanical aortic valve.

Hemodynamic research shows that thrombosis formation is closely tied to flow field turbulent stress. Design limitations cause flow separation at leaflet edges and the annular valve base, vortex mixing downstream, and high turbulent shear stress. The trileaflet design opens like a physiologic valve with central flow.

Computational hemodynamics of an implanted coronary stent based on three-dimensional cine angiography reconstruction.

Coronary stents are supportive wire meshes that keep narrow coronary arteries patent, reducing the risk of restenosis. Despite the common use of coronary stents, approximately 20-35% of them fail due to restenosis. Flow phenomena adjacent to the stent may contribute to restenosis.

On the closing sounds of a mechanical heart valve.

In the 1994 Replacement Heart Valve Guidance of the U.S. Food and Drug Administration (FDA), in-vitro testing is required to evaluate the potential for cavitation damage of a mechanical heart valve (MHV).

Statistical correlation between transient pressure drop and cavitation at closure of a mechanical heart valve.

Cavitation on a mechanical heart valve (MHV) is attributable to transient regional pressure drop at the instant of valve closure. As a cavitation bubble collapses, it emits shock waves, which have the characteristics of high frequency oscillations (HFO) on a pressure time trace. The potential for such HFO bursts to cause material damage on an MHV can be measured by the cavitation impulse I, which is defined as the area under the trace of the HFO bursts.

Statistical characteristics of mechanical heart valve cavitation in accelerated testing.

Background And Aim Of The Study: Cavitation damage has been observed on mechanical heart valves (MHVs) undergoing accelerated testing. Cavitation itself can be modeled as a stochastic process, as it varies from beat to beat of the testing machine. This in-vitro study was undertaken to investigate the statistical characteristics of MHV cavitation.

The closing behavior of mechanical aortic heart valve prostheses.

Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates regurgitation and water hammer effects that may form cavitations, damage blood cells, and cause thromboembolism. This study analyzes closing mechanisms of monoleaflet (Medtronic Hall 27), bileaflet (Carbo-Medics 27; St.

Numerical simulation of opening process in a bileaflet mechanical heart valve under pulsatile flow condition.

Background And Aim Of The Study: Most previous computational fluid dynamics (CFD) studies of blood flow in mechanical heart valves (MHVs) have not efficiently addressed the important features of moving leaflet and blood-leaflet interaction. Herein, computationally efficient approaches were developed to study these features and to obtain better insight into the pulsatile flow field in bileaflet MHVs.

Methods: A simple and effective method to track the moving boundary was proposed, and an efficient method for calculating the blood-leaflet interaction applied.

Bubble observation and transient pressure signals in mechanical heart valve cavitation study.

Background And Aims Of The Study: Cavitation in the mechanical heart valve (MHV) was first detected in Edwards-Duromedics (ED) clinical explants. Early studies indicated that the pitted surface of the valve leaflet was due to cavitation phenomena occurring during valve closing. Cavitation is seen as the transient appearance of bubbles on the MHV surface on valve closure.

Dynamic impact stress analysis of a bileaflet mechanical heart valve.

Background And Aims Of The Study: Mechanical heart valves (MHV) are widely used to replace dysfunctional and failed heart valves. The bileaflet MHV is very popular due to its superior hemodynamics. At present, bileaflet MHVs account for about two-thirds of the prosthetic heart valve market.

Bioprosthetic heart valve leaflet deformation monitored by double-pulse stereo photogrammetry.

A double-pulse stereo photogrammetry technique has been developed for the dynamic assessment of the leaflet deformation of bioprosthetic heart valves under simulated physiological conditions. By using a specially designed triggering technique, which takes the advantage of the field transfer mechanisms of the charge coupled device camera, two consecutive images separated by a time interval as short as 5 ms were captured. This made it possible to investigate the realistic leaflet deformation during the valve opening and closing processes which typically last 25-45 ms.