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

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.

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

Journal of Verification Validation and Uncertainty Quantification ◽

10.1115/1.4042989 ◽

2018 ◽

Vol 3 (4) ◽

Cited By ~ 1

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.

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

Journal of Biomechanical Engineering ◽

10.1115/1.4007092 ◽

2012 ◽

Vol 134 (8) ◽

Cited By ~ 141

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.

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A study on damage to mechanical seat cushion made from different materials of extension frame

International Journal of Engineering & Technology ◽

10.14419/ijet.v7i2.33.14176 ◽

2018 ◽

Vol 7 (3.3) ◽

pp. 315

Author(s):

Jae Won Kim ◽

Jae Ung Cho ◽

Chan Ki Cho ◽

Jin Oh Kim

Keyword(s):

Shear Stress ◽

Statistical Analysis ◽

Material Property ◽

Equivalent Stress ◽

Damage Prediction ◽

Seat Cushion ◽

Seat Cushions

Background/Objectives: : Automotive seat is a very important component to prevent accidents by reducing passenger’s tiredness, thus, this study worked on analyzing damage with different materials of extension frames of mechanical seat cushions.Methods/Statistical analysis: In this study, we performed an experiment on cushion extension frames by splitting it into two parts. We studied about the damage prediction of slave body for each material property of ABS, PP, PLA, and PA6.6. For analyzing the condition, we assigned the side part of the master body for fixed support, and we progressed on analysis by applying with 690N on the entire part of the slave body.Findings: This research worked on the study of damage to different materials of extension frames of seat cushions. After confirming the stress equivalence of the entire model for each material, PP showed the highest equivalent stress of 180.88MPa, and ABS showed the lowest equivalent stress of 151.73MPa. Overall, we could see that in the order of ABS, PA6.6, PLA, PP have a higher tendency to be broken. In addition, when confirming equivalent stress of master body depending on materials of slave body, PA6.6 showed the highest equivalent stress of 166.3MPa, and ABS showed the lowest equivalent stress of 124.06MPa. Overall, we could see that in the order of ABS, PP, PLA and PP6.6 have a higher tendency to be broken. In comparing shear stress on the gear part, which has the highest tendency to be broken in among the entire model, depending on the material of the slave body, PLA showed the greatest shear stress of 88.945MPa, and ABS showed the lowest shear stress of 69.766MPa.Improvements/Applications: This study worked for the improvements and applications of cushion extension frames as the securement of material by investigating these factors.

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Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions

Journal of Fluids Engineering ◽

10.1115/1.1521957 ◽

2003 ◽

Vol 125 (1) ◽

pp. 28-37 ◽

Cited By ~ 28

Author(s):

Ralph J. Volino ◽

Michael P. Schultz ◽

Christopher M. Pratt

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Streamwise Velocity ◽

Turbulent Shear ◽

Conditional Sampling ◽

Freestream Turbulence ◽

Mean Velocity ◽

Transitional Boundary Layer ◽

Turbulent Shear Stress ◽

Order Of Magnitude

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.

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

Volume 3: Biomedical and Biotechnology Engineering ◽

10.1115/imece2017-70850 ◽

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.

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Numerical Model to Predict Hemolysis and Transport in a Membrane-Based Microfluidic Device

10.1101/2020.06.15.152686 ◽

2020 ◽

Author(s):

Matthew D Poskus ◽

Thomas R Gaborski ◽

Steven W Day

Keyword(s):

Patient Outcomes ◽

Shear Stresses ◽

Device Performance ◽

Flow Rates ◽

Blood Damage ◽

Damage Models ◽

Conventional Hemodialysis ◽

Prototype Design ◽

Improve Patient

AbstractMicrofluidic devices may overcome the limitations of conventional hemodialysis and oxygenation technology to improve patient outcomes. Namely, the small form of this technology and parallel development of highly permeable membranes may facilitate the development of portable, low-volume, and efficient alternatives to conventional membrane-based equipment. However, the characteristically small dimensions of these devices may also inhibit transport and may also induce flow-mediated nonphysiologic shear stresses that may damage red blood cells (RBCs). In vitro testing is commonly used to quantify these phenomenon, but is costly and only characterizes bulk device performance. Here we developed a computational model that predicts the blood damage and solute transport for an abitrary microfluidic geometry. We challenged the predictiveness of the model with three geometric variants of a prototype design and validated hemolysis predictions with in vitro blood damge of prototype devices in a recirculating loop. We found that six of the nine tested damage models statistically agree with the experimental data for at least one geometric variant. Additionally, we found that one geometrical variant, the herringbone design, improved toxin (urea) transport to the dialysate by 38% in silico at the expense of a 50% increase in hemolysis. Our work demonstrates that computational modeling may supplement in vitro testing of prototype microdialyzer/micro-oxygenators to expedite the design optimization of these devices. Furthermore, the low device-induced blood damage measured in our study at physiologically relevant flow rates is promising for the future development of microfluidic dialyzers and oxygenators.

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Two-Component Laser Velocimeter Measurements Downstream of Heart Valve Prostheses in Pulsatile Flow

Journal of Biomechanical Engineering ◽

10.1115/1.3138581 ◽

1986 ◽

Vol 108 (1) ◽

pp. 59-64 ◽

Cited By ~ 23

Author(s):

W. G. Tiederman ◽

M. J. Steinle ◽

W. M. Phillips

Keyword(s):

Shear Stress ◽

Pulsatile Flow ◽

Turbulent Shear ◽

Prosthetic Heart Valves ◽

Shear Stresses ◽

Axial Distance ◽

Prosthetic Valves ◽

Disk Valve ◽

Two Component ◽

Stress Levels

Elevated turbulent shear stresses resulting from disturbed blood flow through prosthetic heart valves can cause damage to red blood cells and platelets. The purpose of this study was to measure the turbulent shear stresses occurring downstream of aortic prosthetic valves during in-vitro pulsatile flow. By matching the indices of refraction of the blood analog fluid and model aorta, correlated, simultaneous two-component laser velocimeter measurements of the axial and radial velocity components were made immediately downstream of two aortic prosthetic valves. Velocity data were ensemble averaged over 200 or more cycles for a 15-ms window opened at peak systolic flow. The systolic duration for cardiac flows of 8.4 L/min was 200 ms. Ensemble-averaged total shear stress levels of 2820 dynes/cm2 and 2070 dynes/cm2 were found downstream of a trileaflet valve and a tilting disk valve, respectively. These shear stress levels decreased with axial distance downstream much faster for the tilting disk valve than for the trileaflet valve.

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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

Journal of Biomechanical Engineering ◽

10.1115/1.4027935 ◽

2014 ◽

Vol 136 (9) ◽

Cited By ~ 12

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.

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Non-physiological shear stress-induced blood damage in ventricular assist device

Medicine in Novel Technology and Devices ◽

10.1016/j.medntd.2019.100024 ◽

2019 ◽

Vol 3 ◽

pp. 100024 ◽

Cited By ~ 2

Author(s):

Zengsheng Chen ◽

Anqiang Sun ◽

Hongyu Wang ◽

Yubo Fan ◽

Xiaoyan Deng

Keyword(s):

Shear Stress ◽

Ventricular Assist Device ◽

Assist Device ◽

Ventricular Assist ◽

Blood Damage

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Do megafloods reset mountain valleys?

10.5194/egusphere-egu21-14033 ◽

2021 ◽

Author(s):

Susannah Morey ◽

Katharine Huntington ◽

David Montgomery ◽

Michael Turzewski ◽

Mahathi Mangipudi

Keyword(s):

Shear Stress ◽

Shear Stresses ◽

The Tibetan Plateau ◽

Stream Power ◽

Fractured Bedrock ◽

Fine Grained ◽

Mountain Valley ◽

Order Of Magnitude ◽

High Flood ◽

Peak Flood

Quaternary megafloods (106 m3/s) sourced from valley blocking glaciers on the Tibetan Plateau have long been implicated in the evolution of Yarlung-Tsangpo Gorge on the Yarlung-Siang River. However, past estimates of megaflood erosion in this region have relied on back of the envelope estimates of peak discharge and shear stress. This makes it difficult to fully understand how megafloods shape the landscape. Here, we use 2D numerical simulations of megaflood hydraulics over 3D topography to examine the legacy of these massive floods on this confined, sinuous mountain river. First, to assess erosional potential in the Gorge, we calculate flood power and compare it to measurements of annual stream power. We find that the simulated megaflood produces peak flood power up to three orders of magnitude higher than the stream power of the annual river. Compared to stream power, flood power in the Gorge is disproportionately higher than it is downstream of the Gorge. Additionally, in the Gorge, a larger proportion of the inundated valley experiences high flood power and shear stress for long periods of time (5-10 hrs) compared to the valley downstream of the Gorge. These results support previous hypotheses that megafloods can erode more material (both alluvium and bedrock) than the annual monsoon&#8212;potentially enough to &#8220;reset&#8221; the mountain valley by removing most of the sediment and fractured bedrock in the system. However, we hypothesize that this erosional effect is felt primarily in the Gorge region. In contrast to the erosive power in the Gorge, there is an order of magnitude decrease in average peak flood power downstream of the Gorge. We hypothesize that megafloods are predominantly depositional in this downstream domain. Here, we observe few locations that experience sustained (>5 hrs) high (>10 kPa) shear stress and those locations are often isolated and vary through time. At locations that do experience these higher shear stresses, megafloods could move and deposit large (>3 m) boulders, which subsequent annual flows or smaller historical outburst floods would be incapable of moving. These large boulders could then armor the bed and prevent erosion, which could have lasting consequences for the modern river. Most of the shear stress and flood power of the simulated megaflood outside of the modern channel boundaries are much lower, capable of moving gravel to sand sized sediment at most. This is particularly true where we observe significant amounts (>10 km) of megaflood backflow up tributaries. Instead of resetting the system, we predict our megaflood will overwhelm this downstream flood domain with the deposition of coarse- and fine-grained sediment. For the Yarlung-Siang River to incise into the bedrock in a post-megaflood landscape, it must first make its way through these megaflood deposits. Together, our results suggest that the legacy of a megaflood in the region is both erosional and depositional. We predict wide-spread megaflood erosion in the Gorge, potentially enough to reset the system, but would expect exceptional deposition downstream of it, possibly enough to overwhelm this downstream domain.

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