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.

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.

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.

Computational hemodynamic investigation of a new bileaflet mechanical heart valve

SIMULATION ◽  
2019 ◽  
Vol 96 (5) ◽  
pp. 459-469
Author(s):  
Belkhiri Khellaf ◽  
Boumeddane Boussad
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Stokes Equations ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Blood Damage ◽  
Flow Through

In this paper, we perform a numerical analysis for simulating steady, two-dimensional, laminar blood flow through our proposed design, known as the Butterfly mechanical heart valve, where the leaflets are fully opened. Blood has been assumed to be Newtonian and non-Newtonian fluid using the Casson model for shear-thinning behavior. A non-uniform Cartesian grid generation technique is presented to generate a two-dimensional grid for the irregular geometry of the Butterfly valve. The governing Navier–Stokes equations of flow, written in a stream function–vorticity formulation, are solved by the finite difference method with hybrid differencing of the convective terms. The computed results show that the blood’s non-Newtonian nature significantly affects the flow field with the existence of recirculation and consequently stagnation causing thrombus formation, as well as an increase of the shear stress along the wall, which contributes to hemolytic blood damage. The results demonstrate that the model is capable of predicting the hemodynamic features most interesting to physiologists. It can be used to assess thromboembolic problems occurring with heart valves and in the design of cardiac prostheses.

Comparison of DSMC and CFD Models of Heat Transfer in a Rarefied Two-Dimensional Geometry

2018 ◽  
Author(s):  
Dilesh Maharjan ◽  
Mustafa Hadj-Nacer ◽  
Miles Greiner ◽  
Stefan K. Stefanov
Keyword(s):  
Heat Transfer ◽  
Rarefied Gas ◽  
Complex Geometry ◽  
Direct Simulation Monte Carlo ◽  
Accurate Method ◽  
Vacuum Drying ◽  
Helium Pressure ◽  
Two Dimensional ◽  
Dsmc Method ◽  
Cfd Simulations

During vacuum drying of used nuclear fuel (UNF) canisters, helium pressure is reduced to as low as 67 Pa to promote evaporation and removal of remaining water after draining process. At such low pressure, and considering the dimensions of the system, helium is mildly rarefied, which induces a thermal-resistance temperature-jump at gas–solid interfaces that contributes to the increase of cladding temperature. It is important to maintain the temperature of the cladding below roughly 400 °C to avoid radial hydride formation, which may cause cladding embrittlement during transportation and long-term storage. Direct Simulation Monte Carlo (DSMC) method is an accurate method to predict heat transfer and temperature under rarefied condition. However, it is not convenient for complex geometry like a UNF canister. Computational Fluid Dynamics (CFD) simulations are more convenient to apply but their accuracy for rarefied condition are not well established. This work seeks to validate the use of CFD simulations to model heat transfer through rarefied gas in simple two-dimensional geometry by comparing the results to the more accurate DSMC method. The geometry consists of a circular fuel rod centered inside a square cross-section enclosure filled with rarefied helium. The validated CFD model will be used later to accurately estimate the temperature of an UNF canister subjected to vacuum drying condition.

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.

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.

Design Optimization of a Mechanical Heart Valve for Reducing Valve Thrombogenicity: A Case Study With ATS Valve

2010 ◽  
Author(s):  
Gaurav Girdhar ◽  
Yared Alemu ◽  
Michalis Xenos ◽  
Jawaad Sheriff ◽  
Jolyon Jesty ◽  
...  
Keyword(s):  
Heart Valves ◽  
Thrombus Formation ◽  
Anticoagulation Therapy ◽  
Mechanical Heart Valve ◽  
Ventricular Assist Devices ◽  
Circulatory Support ◽  
Ventricular Assist ◽  
Mechanical Circulatory Support Devices ◽  
Artificial Hearts

Flow past mechanical heart valves (MHV) in mechanical circulatory support devices including total artificial hearts and ventricular assist devices, is primarily implicated in thromboembolism due to non-physiological flow conditions where the elevated stresses and exposure times are sufficiently high to cause platelet activation and thrombus formation. Mitigation of this risk requires lifelong anticoagulation therapy and less thrombogenic MHV designs should therefore be developed by device manufacturers [1].

Argatroban and bivalirudin compared to unfractionated heparin in preventing thrombus formation on mechanical heart valves

2009 ◽  
Vol 101 (06) ◽  
pp. 1163-1169 ◽  
Author(s):  
Torsten Linde ◽  
Thomas Michel ◽  
Kathrin Hamilton ◽  
Ulrich Steinseifer ◽  
Ivar Friedrich ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Unfractionated Heparin ◽  
Continuous Infusion ◽  
Valve Replacement ◽  
Heart Valves ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Mechanical Heart Valves ◽  
Valve Prostheses

SummaryPrevention of valve thrombosis in patients after prosthetic mechanical heart valve replacement and heparin-induced thrombocytopenia (HIT) is still an open issue. The aim of the present in-vitro study was to investigate the efficacy of argatroban and bivalirudin in comparison to unfractionated heparin (UFH) in preventing thrombus formation on mechanical heart valves. Blood (230 ml) from healthy young male volunteers was anticoagulated either by UFH, argatroban bolus, argatroban bolus plus continuous infusion, bivalirudin bolus, or bivalirudin bolus plus continuous infusion. Valve prostheses were placed in a newly developed in-vitro thrombosis tester and exposed to the anticoagulated blood samples. To quantify the thrombi, electron microscopy was performed, and each valve was weighed before and after the experiment. Mean thrombus weight in group 1 (UFH) was 117 + 93 mg, in group 2 (argatroban bolus) 722 + 428 mg, in group 3 (bivalirudin bolus) 758 + 323 mg, in group 4 (argatroban bolus plus continuous infusion) 162 + 98 mg, and in group 5 (bivalirudin bolus plus continuous infusion) 166 + 141 mg (p-value <0.001). Electron microscopy showed increased rates of thrombus formation in groups 2 and 3. Argatroban and bivalirudin were as effective as UFH in preventing thrombus formation on valve prostheses in our in-vitro investigation when they were administered continuously. We hypothesise that continuous infusion of argatroban or bivalirudin are optimal treatment options for patients with HIT after mechanical heart valve replacement for adapting oral to parenteral anticoagulation or vice versa.

scholarly journals Effect of the Alterations in Contractility and Morphology Produced by Atrial Fibrillation on the Thrombosis Potential of the Left Atrial Appendage

2021 ◽  
Vol 9 ◽  
Author(s):  
Danila Vella ◽  
Alessandra Monteleone ◽  
Giulio Musotto ◽  
Giorgia Maria Bosi ◽  
Gaetano Burriesci
Keyword(s):  
Atrial Fibrillation ◽  
Left Atrium ◽  
Left Atrial ◽  
Left Atrial Appendage ◽  
Thrombus Formation ◽  
Fluid Dynamic ◽  
Atrial Appendage ◽  
Primary Role ◽  
Shear Strain Rate ◽  
Increased Risk

Atrial fibrillation (AF) is a common arrhythmia mainly affecting the elderly population, which can lead to serious complications such as stroke, ischaemic attack and vascular dementia. These problems are caused by thrombi which mostly originate in the left atrial appendage (LAA), a small muscular sac protruding from left atrium. The abnormal heart rhythm associated with AF results in alterations in the heart muscle contractions and in some reshaping of the cardiac chambers. This study aims to verify if and how these physiological changes can establish hemodynamic conditions in the LAA promoting thrombus formation, by means of computational fluid dynamic (CFD) analyses. In particular, sinus and fibrillation contractility was replicated by applying wall velocity/motion to models based on healthy and dilated idealized shapes of the left atrium with a common LAA morphology. The models were analyzed and compared in terms of shear strain rate (SSR) and vorticity, which are hemodynamic parameters directly associated with thrombogenicity. The study clearly indicates that the alterations in contractility and morphology associated with AF pathologies play a primary role in establishing hemodynamic conditions which promote higher incidence of ischaemic events, consistently with the clinical evidence. In particular, in the analyzed models, the impairment in contractility determined a decrease in SSR of about 50%, whilst the chamber pathological dilatation contributed to a 30% reduction, indicating increased risk of clot formation. The equivalent rigid wall model was characterized by SSR values about one order of magnitude smaller than in the contractile models, and substantially different vortical behavior, suggesting that analyses based on rigid chambers, although common in the literature, are inadequate to provide realistic results on the LAA hemodynamics.

scholarly journals Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2204 ◽  
Author(s):  
Hosseiny ◽  
Smith
Keyword(s):  
Urban Areas ◽  
Water Surface ◽  
Integrated Model ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Morphological Alterations ◽  
Digital Elevation ◽  
Starting Point ◽  
Spatio Temporal ◽  
Elevation Model

Predicting morphological alterations in backwater zones has substantial merit as it potentially influences the life of millions of people by the change in flood dynamics and land topography. While there is no two-dimensional river model available for predicting morphological alterations in backwater zones, there is an absolute need for such models. This study presents an integrated iterative two-dimensional fluvial morphological model to quantify spatio-temporal fluvial morphological alterations in normal flow to backwater conditions. The integrated model works through the following steps iteratively to derive geomorphic change: (1) iRIC model is used to generate a 2D normal water surface; (2) a 1D water surface is developed for the backwater; (3) the normal and backwater surfaces are integrated; (4) an analytical 2D model is established to estimate shear stresses and morphological alterations in the normal, transitional, and backwater zones. The integrated model generates a new digital elevation model based on the estimated erosion and deposition. The resultant topography then serves as the starting point for the next iteration of flow, ultimately modeling geomorphic changes through time. This model was tested on Darby Creek in Metro-Philadelphia, one of the most flood-prone urban areas in the US and the largest freshwater marsh in Pennsylvania.

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