scholarly journals Two-Dimensional FSI Simulation of Closing Dynamics of a Tilting Disk Mechanical Heart Valve

2010 ◽  
Vol 4 (1) ◽  
Author(s):  
V. Govindarajan ◽  
H. S. Udaykumar ◽  
L. H. Herbertson ◽  
S. Deutsch ◽  
K. B. Manning ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Interaction Analysis ◽  
Mechanical Heart Valve ◽  
Shear Stresses ◽  
Particle Dynamic ◽  
Valve Closure ◽  
Two Dimensional ◽  
Disk Valve ◽  
Bileaflet Mechanical Valve ◽  
Valve Housing

The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bileaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and valve housing results in relatively high platelet activation levels, whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disk valve with that of a bileaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disk valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime, and the flow through the gap width is marked by the development of a shear layer, which separates from the leaflet downstream of the valve. Zones of recirculation are observed in the gap between the leaflet edge and valve housing on the major orifice region of the tilting disk valve and are seen to be migrating toward the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed, which sheds in the direction of fluid motion, as observed in experiments using PIV measurements. The activation parameter computed for the tilting disk valve at the time of closure was found to be 2.7 times greater than that of the bileaflet mechanical valve and was found to be in the vicinity of the minor orifice region, mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase.

scholarly journals Two-Dimensional Simulation of Flow and Platelet Dynamics in the Hinge Region of a Mechanical Heart Valve

2008 ◽  
Vol 131 (3) ◽  
Author(s):  
V. Govindarajan ◽  
H. S. Udaykumar ◽  
K. B. Chandran
Keyword(s):  
Complex Geometry ◽  
Interaction Analysis ◽  
Thrombus Formation ◽  
Fluid Dynamic ◽  
Mechanical Heart Valve ◽  
Hinge Region ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Bileaflet Mechanical Valve ◽  
Bileaflet Valve

The hinge region of a mechanical bileaflet valve is implicated in blood damage and initiation of thrombus formation. Detailed fluid dynamic analysis in the complex geometry of the hinge region during the closing phase of the bileaflet valve is the focus of this study to understand the effect of fluid-induced stresses on the activation of platelets. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a two-dimensional geometry of the hinge region of a bileaflet mechanical valve. Use of local mesh refinement algorithm provides mesh adaptation based on the gradients of flow in the constricted geometry of the hinge. Leaflet motion is specified from the fluid-structure interaction analysis of the leaflet dynamics during the closing phase from a previous study, which focused on the fluid mechanics at the gap between the leaflet edges and the valve housing. A Lagrangian particle tracking method is used to model and track the platelets and to compute the magnitude of the shear stress on the platelets as they pass through the hinge region. Results show that there is a boundary layer separation in the gaps between the leaflet ear and the constricted hinge geometry. Separated shear layers roll up into vortical structures that lead to high residence times combined with exposure to high-shear stresses for particles in the hinge region. Particles are preferentially entrained into this recirculation zone, presenting the possibility of platelet activation, aggregation, and initiation of thrombi.

Two-Dimensional Simulation of Platelet Activation in the Hinge Region of a Mechanical Heart Valve

2007 ◽  
Author(s):  
V. Govindarajan ◽  
H. S. Udaykumar ◽  
K. B. Chandran
Keyword(s):  
Platelet Activation ◽  
Complex Geometry ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Mechanical Valve ◽  
Hinge Region ◽  
Valve Closure ◽  
Flow Through ◽  
Valve Housing ◽  
Squeezed Flow

The proper functioning of the leaflets of a bi-leaflet mechanical valve requires the use of the hinge mechanism which lets the leaflets pivot to the valve housing and lets it rotate at a specified angle. It has been pointed that the hinge design directly affects the durability of the valve [1]. In Bi-leaflet valves the thrombus formation is mostly observed in the hinge region and also on the valve housing [2]. This may be due to the complex geometry presented by the hinge region, which makes the flow complex making the hinge region a potential site for thrombus formation and accumulation which could pose a threat to the efficient functioning of the valve itself. It was hypothesized that the flow fields with in the hinge region played a major role in thrombus accumulation in the Medtronic parallel valve [3]. Studies have demonstrated that fluid dynamics in the vicinity of valve leaflet and housing at the instant of valve closure may lead to large negative pressure transients across the leaflets [4]. These large pressure gradients present for a small duration of time induces very high velocity squeezed flow through the clearance region between the valve housing and the leaflet tip and through the gaps in the hinge region which has been provided for rotation of the leaflet and washout. The wall shear stress in these regions can be relatively high during the closure phase resulting in platelet activation. This study will focus on the flow through the hinge region and its effect on the platelet activation during the valve closure under Mitral conditions which is the harshest environment for a valve.

Two-Dimensional Dynamic Simulation of Platelet Activation During Mechanical Heart Valve Closure

2006 ◽  
Vol 34 (10) ◽  
pp. 1519-1534 ◽  
Author(s):  
S. Krishnan ◽  
H. S. Udaykumar ◽  
J. S. Marshall ◽  
K. B. Chandran
Keyword(s):  
Dynamic Simulation ◽  
Heart Valve ◽  
Platelet Activation ◽  
Mechanical Heart Valve ◽  
Valve Closure ◽  
Two Dimensional

scholarly journals The Effect of Turbulence Modelling on the Assessment of Platelet Activation

2020 ◽  
Author(s):  
Silvia Bozzi ◽  
Davide Dominissini ◽  
Alberto Redaelli ◽  
Giuseppe Passoni
Keyword(s):  
Fluid Dynamics ◽  
Mathematical Models ◽  
Platelet Activation ◽  
Mechanical Heart Valve ◽  
Turbulence Modelling ◽  
Shear Stresses ◽  
Large Variability ◽  
Frequency Distributions ◽  
Lagrangian Variables ◽  
Turbulence Closures

Abstract Pathological platelet activation induced by abnormal shear stresses is regarded as a main clinical complication in recipients of cardiovascular biomedical implantable devices and prostheses. In order to improve their performance computational fluid dynamics (CFD) has been used to evaluate flow fields and related shear stresses. More recently CFD models have been equipped with mathematical models that describe the relation between fluid dynamics variables, and in particular shear stresses, and the platelet activation state (PAS). These mathematical models typically use a Lagrangian approach to extract the shear stresses along possible platelet trajectories. However, in the case of turbulent flow, the choice of the proper turbulence closure model is still debated for both concerning its effect on Lagrangian statistics and shear stress calculation. In our study five numerical simulations of the flow through a mechanical heart valve were performed and then compared in terms of Eulerian and Lagrangian quantities: a direct numerical simulation (DNS), a large eddy simulation (LES), two Reynolds-averaged Navier-Stokes (RANS) simulations (SST k-ω and RSM) and a “Laminar” (no turbulence modelling on a Taylor microscale-based grid) simulation. Results exhibit a large variability in the PAS assessment depending on the turbulence model adopted. “Laminar” and RSM estimates of platelet activation are about 60% below DNS, while LES is 16% less. Surprisingly, PAS estimated from the SST k-ω velocity field is only 8% less than from DNS data. This appears more artificial than physical as can be inferred after comparing frequency distributions of PAS and of the different Lagrangian variables of the mechano-biological model of platelet activation. Our study indicates that turbulence closures can lead to a severe underestimation of platelet activation and suggests that turbulence should be fully resolved by DNS when assessing blood damage in blood contacting devices.

Reduction of Flow-Induced Blood Damage in Bileaflet Mechanical Heart Valves Through Passive Flow Control

2008 ◽  
Author(s):  
David W. Murphy ◽  
Lakshmi P. Dasi ◽  
Ari Glezer ◽  
Ajit P. Yoganathan
Keyword(s):  
Shear Stress ◽  
Platelet Activation ◽  
Heart Valves ◽  
Vortex Generators ◽  
Mechanical Heart Valves ◽  
Shear Stresses ◽  
Valve Closure ◽  
Passive Flow Control ◽  
Blood Damage ◽  
Passive Flow

Bileaflet mechanical heart valves (BMHVs), though a life-saving device in treating heart valve disease, are often associated with several complications including a high risk of hemolysis, platelet activation, and thromboembolism. To address this risk, patients must undergo prophylactic anticoagulation therapy. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation [1–3]. Reducing the shear stresses experienced by the blood flowing through the b-datum gap during valve closure may therefore reduce the prevalence of valve-related blood damage. Such shear stress reduction could be achieved by passive flow control, in particular vortex generators, incorporated onto the BMHV leaflet surface. Vortex generators have been used to control shear flows in various aerodynamic applications, and it is thus thought that their application to mechanical heart valve leaflet surfaces may reduce shear stresses by creating streamwise vortices that will serve to dissipate the regurgitant jet originating from the b-datum gap at the time of valve closure.

Fluid Mechanical Analysis at Closure of the On-X Mechanical Heart Valve

2007 ◽  
Author(s):  
Christopher M. Haggerty ◽  
Luke H. Herbertson ◽  
Steven Deutsch ◽  
Keefe B. Manning
Keyword(s):  
Heart Valve ◽  
Mechanical Heart Valve ◽  
Three Dimensional ◽  
Mechanical Analysis ◽  
Shear Stresses ◽  
Single Shot ◽  
Complex Flow ◽  
Mitral Position ◽  
Valve Housing ◽  
The Impact

Three-dimensional laser Doppler velocimetry (LDV) was used to characterize the flow created by the On-X bileaflet mechanical heart valve (MHV) manufactured by Medical Carbon Research Institute (MCRI), Inc. (Austin, TX). The valve was mounted into a pneumatically driven single-shot chamber in the mitral position such that only the closure dynamics were simulated. Measurements taken 2 mm proximal to the valve housing showed a peak velocity of 1.8 m/s and maximum Reynolds Shear Stresses (RSS) of 17,500 dynes/cm2, which were found along the centerline of the valve in the hinge region 2 ms after valve closure. The large velocity and RSS gradients denote the presence of complex flow structures. These results provide an initial basis for understanding the impact of valve geometry on hemolysis and thrombosis associated with the On-X MHV.

Numerical study of electric field effects on the deformation of two-dimensional liquid drops in simple shear flow at arbitrary Reynolds number

2009 ◽  
Vol 626 ◽  
pp. 367-393 ◽  
Author(s):  
STEFAN MÄHLMANN ◽  
DEMETRIOS T. PAPAGEORGIOU
Keyword(s):  
Steady State ◽  
Shear Flow ◽  
Electric Field ◽  
Electric Fields ◽  
Simple Shear ◽  
Simple Shear Flow ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Liquid Drops

The effect of an electric field on a periodic array of two-dimensional liquid drops suspended in simple shear flow is studied numerically. The shear is produced by moving the parallel walls of the channel containing the fluids at equal speeds but in opposite directions and an electric field is generated by imposing a constant voltage difference across the channel walls. The level set method is adapted to electrohydrodynamics problems that include a background flow in order to compute the effects of permittivity and conductivity differences between the two phases on the dynamics and drop configurations. The electric field introduces additional interfacial stresses at the drop interface and we perform extensive computations to assess the combined effects of electric fields, surface tension and inertia. Our computations for perfect dielectric systems indicate that the electric field increases the drop deformation to generate elongated drops at steady state, and at the same time alters the drop orientation by increasing alignment with the vertical, which is the direction of the underlying electric field. These phenomena are observed for a range of values of Reynolds and capillary numbers. Computations using the leaky dielectric model also indicate that for certain combinations of electric properties the drop can undergo enhanced alignment with the vertical or the horizontal, as compared to perfect dielectric systems. For cases of enhanced elongation and alignment with the vertical, the flow positions the droplets closer to the channel walls where they cause larger wall shear stresses. We also establish that a sufficiently strong electric field can be used to destabilize the flow in the sense that steady-state droplets that can exist in its absence for a set of physical parameters, become increasingly and indefinitely elongated until additional mechanisms can lead to rupture. It is suggested that electric fields can be used to enhance such phenomena.

Multiscale Modeling of Flow Induced Thrombogenicity Using Dissipative Particle Dynamics and Molecular Dynamics

2013 ◽  
Author(s):  
Danny Bluestein ◽  
João S. Soares ◽  
Peng Zhang ◽  
Chao Gao ◽  
Seetha Pothapragada ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Blood Flow ◽  
Red Blood Cells ◽  
Platelet Activation ◽  
Blood Cells ◽  
Dissipative Particle Dynamics ◽  
Particle Dynamics ◽  
Coagulation Cascade ◽  
Shear Stresses ◽  
Activated Platelets

The coagulation cascade of blood may be initiated by flow induced platelet activation, which prompts clot formation in prosthetic cardiovascular devices and arterial disease processes. While platelet activation may be induced by biochemical agonists, shear stresses arising from pathological flow patterns enhance the propensity of platelets to activate and initiate the intrinsic pathway of coagulation, leading to thrombosis. Upon activation platelets undergo complex biochemical and morphological changes: organelles are centralized, membrane glycoproteins undergo conformational changes, and adhesive pseudopods are extended. Activated platelets polymerize fibrinogen into a fibrin network that enmeshes red blood cells. Activated platelets also cross-talk and aggregate to form thrombi. Current numerical simulations to model this complex process mostly treat blood as a continuum and solve the Navier-Stokes equations governing blood flow, coupled with diffusion-convection-reaction equations. It requires various complex constitutive relations or simplifying assumptions, and is limited to μm level scales. However, molecular mechanisms governing platelet shape change upon activation and their effect on rheological properties can be in the nm level scales. To address this challenge, a multiscale approach which departs from continuum approaches, may offer an effective means to bridge the gap between macroscopic flow and cellular scales. Molecular dynamics (MD) and dissipative particle dynamics (DPD) methods have been employed in recent years to simulate complex processes at the molecular scales, and various viscous fluids at low-to-high Reynolds numbers at mesoscopic scales. Such particle methods possess important properties at the mesoscopic scale: complex fluids with heterogeneous particles can be modeled, allowing the simulation of processes which are otherwise very difficult to solve by continuum approaches. It is becoming a powerful tool for simulating complex blood flow, red blood cells interactions, and platelet-mediated thrombosis involving platelet activation, aggregation, and adhesion.

scholarly journals Effects of Bileaflet Mechanical Mitral Valve Rotational Orientation on Left Ventricular Flow Conditions

2015 ◽  
Vol 9 (1) ◽  
pp. 62-68 ◽  
Author(s):  
John C Westerdale ◽  
Ronald Adrian ◽  
Kyle Squires ◽  
Hari Chaliki ◽  
Marek Belohlavek
Keyword(s):  
Velocity Field ◽  
Measurement Techniques ◽  
Angular Position ◽  
Mechanical Heart Valve ◽  
Mechanical Valve ◽  
Left Ventricular ◽  
Shear Stresses ◽  
Elastic Model ◽  
Intraventricular Flow ◽  
Particle Imaging

We studied left ventricular flow patterns for a range of rotational orientations of a bileaflet mechanical heart valve (MHV) implanted in the mitral position of an elastic model of a beating left ventricle (LV). The valve was rotated through 3 angular positions (0, 45, and 90 degrees) about the LV long axis. Ultrasound scans of the elastic LV were obtained in four apical 2-dimensional (2D) imaging projections, each with 45 degrees of separation. Particle imaging velocimetry was performed during the diastolic period to quantify the in-plane velocity field obtained by computer tracking of diluted microbubbles in the acquired ultrasound projections. The resulting velocity field, vorticity, and shear stresses were statistically significantly altered by angular positioning of the mechanical valve, although the results did not show any specific trend with the valve angular position and were highly dependent on the orientation of the imaging plane with respect to the valve. We conclude that bileaflet MHV orientation influences hemodynamics of LV filling. However, determination of ‘optimal’ valve orientation cannot be made without measurement techniques that account for the highly 3-dimensional (3D) intraventricular flow.

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