scholarly journals Effect of Hinge Gap Width of a St. Jude Medical Bileaflet Mechanical Heart Valve on Blood Damage Potential—An In Vitro Micro Particle Image Velocimetry Study

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Brian H. Jun ◽  
Neelakantan Saikrishnan ◽  
Sivakkumar Arjunon ◽  
B. Min Yun ◽  
Ajit P. Yoganathan
Keyword(s):  
Shear Stress ◽  
Mechanical Heart Valve ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Damage Potential ◽  
Jude Medical ◽  
Blood Damage ◽  
Micro Particle Image Velocimetry ◽  
Flow Stasis ◽  
Gap Width

The hinge regions of the bileaflet mechanical heart valve (BMHV) can cause blood element damage due to nonphysiological shear stress levels and regions of flow stasis. Recently, a micro particle image velocimetry (μPIV) system was developed to study whole flow fields within BMHV hinge regions with enhanced spatial resolution under steady leakage flow conditions. However, global velocity maps under pulsatile conditions are still necessary to fully understand the blood damage potential of these valves. The current study hypothesized that the hinge gap width will affect flow fields in the hinge region. Accordingly, the blood damage potential of three St. Jude Medical (SJM) BMHVs with different hinge gap widths was investigated under pulsatile flow conditions, using a μPIV system. The results demonstrated that the hinge gap width had a significant influence during the leakage flow phase in terms of washout and shear stress characteristics. During the leakage flow, the largest hinge gap generated the highest Reynolds shear stress (RSS) magnitudes (∼1000 N/m2) among the three valves at the ventricular side of the hinge. At this location, all three valves indicated viscous shear stresses (VSS) greater than 30 N/m2. The smallest hinge gap exhibited the lowest level of shear stress values, but had the poorest washout flow characteristics among the three valves, demonstrating propensity for flow stasis and associated activated platelet accumulation potential. The results from this study indicate that the hinge is a critical component of the BMHV design, which needs to be optimized to find the appropriate balance between reduction in fluid shear stresses and enhanced washout during leakage flow, to ensure minimal thrombotic complications.

scholarly journals Blood Damage Through a Bileaflet Mechanical Heart Valve: A Quantitative Computational Study Using a Multiscale Suspension Flow Solver

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
B. Min Yun ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Numerical Method ◽  
Heart Valves ◽  
Computational Study ◽  
Mechanical Heart Valve ◽  
Complex Flow ◽  
Damage Potential ◽  
Spatiotemporal Resolution ◽  
Jude Medical ◽  
Blood Damage ◽  
Flow Through

Bileaflet mechanical heart valves (BMHVs) are among the most popular prostheses to replace defective native valves. However, complex flow phenomena caused by the prosthesis are thought to induce serious thromboembolic complications. This study aims at employing a novel multiscale numerical method that models realistic sized suspended platelets for assessing blood damage potential in flow through BMHVs. A previously validated lattice-Boltzmann method (LBM) is used to simulate pulsatile flow through a 23 mm St. Jude Medical (SJM) Regent™ valve in the aortic position at very high spatiotemporal resolution with the presence of thousands of suspended platelets. Platelet damage is modeled for both the systolic and diastolic phases of the cardiac cycle. No platelets exceed activation thresholds for any of the simulations. Platelet damage is determined to be particularly high for suspended elements trapped in recirculation zones, which suggests a shift of focus in blood damage studies away from instantaneous flow fields and toward high flow mixing regions. In the diastolic phase, leakage flow through the b-datum gap is shown to cause highest damage to platelets. This multiscale numerical method may be used as a generic solver for evaluating blood damage in other cardiovascular flows and devices.

Eulerian-Eulerian Multiphase Modeling of Blood Cells Segregation in Flow Through Microtubes

2017 ◽  
Author(s):  
Yertay Mendygarin ◽  
Luis R. Rojas-Solórzano ◽  
Nurassyl Kussaiyn ◽  
Rakhim Supiyev ◽  
Mansur Zhussupbekov
Keyword(s):  
Shear Stress ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Heart Diseases ◽  
Accurate Determination ◽  
Shear Stresses ◽  
High Shear ◽  
Blood Damage ◽  
Solid Phases

Cardiovascular Diseases, the common name for various Heart Diseases, are responsible for nearly 17.3 million deaths annually and remain the leading global cause of death in the world. It is estimated that this number will grow to more than 23.6 million by 2030, with almost 80% of all cases taking place in low and middle income countries. Surgical treatment of these diseases involves the use of blood-wetted devices, whose relatively recent development has given rise to numerous possibilities for design improvements. However, blood can be damaged when flowing through these devices due to the lack of biocompatibility of surrounding walls, thermal and osmotic effects and most prominently, due to the excessive exposure of blood cells to shear stress for prolonged periods of time. This extended exposure may lead to a rupture of membrane of red blood cells, resulting in a release of hemoglobin into the blood plasma, in a process called hemolysis. Moreover, exposure of platelets to high shear stresses can increase the likelihood of thrombosis. Therefore, regions of high shear stress and residence time of blood cells must be considered thoroughly during the design of blood-contacting devices. Though laboratory tests are vital for design improvements, in-vitro experiments have proven to be costly, time-intensive and ethically controversial. On the other hand, simulating blood behavior using Computational Fluid Dynamics (CFD) is considered to be an inexpensive and promising tool to help predicting blood damage in complex flows. Nevertheless, current state-of-the-art CFD models of blood flow to predict hemolysis are still far from being fully reliable and accurate for design purposes. Previous work have demonstrated that prediction of hemolysis can be dramatically improved when using a multiphase (i.e., phases are plasma, red blood cells and platelets) model of the blood instead of assuming the blood as a homogeneous mixture. Nonetheless, the accurate determination of how the cells segregate becomes the critical issue in reaching a truthful prediction of blood damage. Therefore, the attempt of this study is to develop and validate a numerical model based on Granular Kinetic Theory (GKT) for solid phases (i.e., cells treated as particles) that provides an improved prediction of blood cells segregation within the flow in a microtube. Simulations were based on finite volume method using Eulerian-Eulerian modeling for treatment of three-phase (liquid-red blood cells and platelets) flow including the GKT to deal with viscous properties of the solid phases. GKT proved to be a good model to predict particle concentration and pressure drop by taking into account the contribution of collisional, kinetic and frictional effects in the stress tensor of the segregated solid phases. Preliminary results show that the improved segregated model leads to a better prediction of spatial distribution of blood cells. Simulations were performed using ANSYS FLUENT platform.

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

2019 ◽  
Vol 42 (12) ◽  
pp. 735-747 ◽  
Author(s):  
Benjamin Torner ◽  
Lucas Konnigk ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Equivalent Stress ◽  
Volumetric Analysis ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Ventricular Assist ◽  
Damage Prediction ◽  
Blood Damage ◽  
Damage Models ◽  
Order Of Magnitude

The blood damage prediction in rotary blood pumps is an important procedure to evaluate the hemocompatibility of such systems. Blood damage is caused by shear stresses to the blood cells and their exposure times. The total impact of an equivalent shear stress can only be taken into account when turbulent stresses are included in the blood damage prediction. The aim of this article was to analyze the influence of the turbulent stresses on the damage prediction in a rotary blood pump’s flow. Therefore, the flow in a research blood pump was computed using large eddy simulations. A highly turbulence-resolving setup was used in order to directly resolve most of the computed stresses. The simulations were performed at the design point and an operation point with lower flow rate. Blood damage was predicted using three damage models (volumetric analysis of exceeded stress thresholds, hemolysis transport equation, and hemolysis approximation via volume integral) and two shear stress definitions (with and without turbulent stresses). For both simulations, turbulent stresses are the dominant stresses away from the walls. Here, they act in a range between 9 and 50 Pa. Nonetheless, the mean stresses in the proximity of the walls reach levels, which are one order of magnitude higher. Due to this, the turbulent stresses have a small impact on the results of the hemolysis prediction. Yet, turbulent stresses should be included in the damage prediction, since they belong to the total equivalent stress definition and could impact the damage on proteins or platelets.

Grid-Induced Numerical Errors for Shear Stresses and Essential Flow Variables in a Ventricular Assist Device: Crucial for Blood Damage Prediction?

2018 ◽  
Vol 3 (4) ◽  
Author(s):  
Lucas Konnigk ◽  
Benjamin Torner ◽  
Sebastian Hallier ◽  
Matthias Witte ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Prediction Models ◽  
Stokes Equations ◽  
Grid Size ◽  
Blood Pump ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Damage Prediction ◽  
Blood Damage ◽  
Stress Calculation

Adverse events due to flow-induced blood damage remain a serious problem for blood pumps as cardiac support systems. The numerical prediction of blood damage via computational fluid dynamics (CFD) is a helpful tool for the design and optimization of reliable pumps. Blood damage prediction models primarily are based on the acting shear stresses, which are calculated by solving the Navier–Stokes equations on computational grids. The purpose of this paper is to analyze the influence of the spatial discretization and the associated discretization error on the shear stress calculation in a blood pump in comparison to other important flow quantities like the pressure head of the pump. Therefore, CFD analysis using seven unsteady Reynolds-averaged Navier–Stokes (URANS) simulations was performed. Two simple stress calculation indicators were applied to estimate the influence of the discretization on the results using an approach to calculate numerical uncertainties, which indicates discretization errors. For the finest grid with 19 × 106 elements, numerical uncertainties up to 20% for shear stresses were determined, while the pressure heads show smaller uncertainties with a maximum of 4.8%. No grid-independent solution for velocity gradient-dependent variables could be obtained on a grid size that is comparable to mesh sizes in state-of-the-art blood pump studies. It can be concluded that the grid size has a major influence on the shear stress calculation, and therefore, the potential blood damage prediction, and that the quantification of this error should always be taken into account.

scholarly journals A Quantitative Comparison of Mechanical Blood Damage Parameters in Rotary Ventricular Assist Devices: Shear Stress, Exposure Time and Hemolysis Index

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Katharine H. Fraser ◽  
Tao Zhang ◽  
M. Ertan Taskin ◽  
Bartley P. Griffith ◽  
Zhongjun J. Wu
Keyword(s):  
Shear Stress ◽  
Platelet Activation ◽  
Exposure Time ◽  
Ventricular Assist Devices ◽  
Shear Stresses ◽  
Residence Times ◽  
Stress Exposure ◽  
Ventricular Assist ◽  
Assist Devices ◽  
Blood Damage

Ventricular assist devices (VADs) have already helped many patients with heart failure but have the potential to assist more patients if current problems with blood damage (hemolysis, platelet activation, thrombosis and emboli, and destruction of the von Willebrand factor (vWf)) can be eliminated. A step towards this goal is better understanding of the relationships between shear stress, exposure time, and blood damage and, from there, the development of numerical models for the different types of blood damage to enable the design of improved VADs. In this study, computational fluid dynamics (CFD) was used to calculate the hemodynamics in three clinical VADs and two investigational VADs and the shear stress, residence time, and hemolysis were investigated. A new scalar transport model for hemolysis was developed. The results were compared with in vitro measurements of the pressure head in each VAD and the hemolysis index in two VADs. A comparative analysis of the blood damage related fluid dynamic parameters and hemolysis index was performed among the VADs. Compared to the centrifugal VADs, the axial VADs had: higher mean scalar shear stress (sss); a wider range of sss, with larger maxima and larger percentage volumes at both low and high sss; and longer residence times at very high sss. The hemolysis predictions were in agreement with the experiments and showed that the axial VADs had a higher hemolysis index. The increased hemolysis in axial VADs compared to centrifugal VADs is a direct result of their higher shear stresses and longer residence times. Since platelet activation and destruction of the vWf also require high shear stresses, the flow conditions inside axial VADs are likely to result in more of these types of blood damage compared with centrifugal VADs.

Mesh Sensitivity Analysis for Quantitative Shear Stress Assessment in Blood Pumps Using Computational Fluid Dynamics

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Sascha Gross-Hardt ◽  
Fiete Boehning ◽  
Ulrich Steinseifer ◽  
Thomas Schmitz-Rode ◽  
Tim A. S. Kaufmann
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Transport Model ◽  
Leading Edge ◽  
Characteristic Number ◽  
Tip Clearance ◽  
Shear Stresses ◽  
Centrifugal Blood Pump ◽  
Blood Damage

The reduction of excessive, nonphysiologic shear stresses leading to blood trauma can be the key to overcome many of the associated complications in blood recirculating devices. In that regard, computational fluid dynamics (CFD) are gaining in importance for the hydraulic and hemocompatibility assessment. Still, direct hemolysis assessments with CFD remain inaccurate and limited to qualitative comparisons rather than quantitative predictions. An underestimated quantity for improved blood damage prediction accuracy is the influence of near-wall mesh resolution on shear stress quantification in regions of complex flows. This study investigated the necessary mesh refinement to quantify shear stress for two selected, meshing sensitive hotspots within a rotary centrifugal blood pump (the blade leading edge and tip clearance gap). The shear stress in these regions is elevated due to presence of stagnation points and the flow around a sharp edge. The nondimensional mesh characteristic number y+, which is known in the context of turbulence modeling, underestimated the maximum wall shear stress by 60% on average with the recommended value of 1, but was found to be exact below 0.1. To evaluate the meshing related error on the numerical hemolysis prediction, three-dimensional simulations of a generic centrifugal pump were performed with mesh sizes from 3 × 106 to 30 × 106 elements. The respective hemolysis was calculated using an Eulerian scalar transport model. Mesh insensitivity was found below a maximum y+ of 0.2 necessitating 18 × 106 mesh elements. A meshing related error of up to 25% was found for the coarser meshes. Further investigations need to address: (1) the transferability to other geometries and (2) potential adaptions on blood damage estimation models to allow better quantitative predictions.

scholarly journals A Computational Study of a Passive Flow Device in a Mechanical Heart Valve for the Anatomic Aorta and the Axisymmetric Aorta

CFD letters ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 69-79
Author(s):  
Nursyaira Mohd Salleh ◽  
Mohamad Shukri Zakaria ◽  
Mohd Juzaila Abd Latif ◽  
Adi Azriff Basri
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Heart Valve ◽  
Heart Valves ◽  
Computational Study ◽  
Mechanical Heart Valve ◽  
Vortex Generator ◽  
Leading Edge ◽  
Jude Medical ◽  
Wall Shear

Artificial heart valves for replacing diseased indigenous heart valves were widely used. The treatment of certain types of heart disease requires mechanical valves to be implanted operatively. Healthy cardiac valves are essential to proper cardiac function. The current study presents an investigation of the pulsatile blood flow through a bileaflet mechanical heart valve (BMHV) with a vortex generator (VG) in fully open position. A St. Jude Medical Regent valve with a diameter of 23 mm was used to mount triangular VGs as a means of improving pressure gradients and reducing turbulence. The anatomic aorta and axisymmetric aorta was computed by large eddy simulation (LES) approached. The implications for both models with VGs were observed in terms of velocity magnitude, vortices and wall shear stress. The results suggested that the anatomic aorta is prone to develop more blood clotting at the leading edge of the leaflets with 2.03 m/s. Furthermore, the anatomic aorta produces higher wall shear stress with 69Pa, which possibly contributes to a high risk of thrombosis.

Blood Damage Quantification in Cardiovascular Flows Through Medical Devices Using a Novel Suspension Flow Method

2013 ◽  
Author(s):  
B. Min Yun ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Mechanical Heart Valve ◽  
Alternative Methods ◽  
Suspension Flow ◽  
Spatiotemporal Resolution ◽  
Flow Solver ◽  
Jude Medical ◽  
Blood Damage ◽  
Bileaflet Mechanical Heart Valve ◽  
Damage Quantification ◽  
Baseline Case

A numerical suspension flow solver is presented that can accurately quantify blood damage in cardiovascular flows. This method is capable of high spatiotemporal resolution simulations with optimal parallel computing. In addition, the method models realistic platelets for more accurate damage quantification compared to alternative methods. The numerical tool is tested on a baseline case of a St. Jude Medical bileaflet mechanical heart valve, and blood damage results are analyzed in both Lagrangian and Eulerian viewpoints.

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.

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