NUMERICAL SIMULATION OF THE EFFECT OF VENOUS NEEDLE'S FLOW RATE AND ANGLE ON FLOW PARAMETERS OF A HEMODIALYSIS GRAFT

2015 ◽  
Vol 27 (05) ◽  
pp. 1550048
Author(s):  
N. Meghdadi ◽  
H. Niroomand-Oscuii
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Rate ◽  
Intimal Hyperplasia ◽  
Venous Access ◽  
Venous Anastomosis ◽  
Flow Rates ◽  
Graft Stenosis ◽  
Wall Shear ◽  
Hemodialysis Graft

Arterio-Venous grafts, which are used for hemodialysis, frequently develop intimal hyperplasia in venous anastomosis which ultimately leads to graft failure. It is observed in different studies that the wall shear stress can be correlated to intimal hyperplasia development. Although high Arterio-Venous access blood flow has been implicated in the pathogenesis of graft stenosis, the role of needle's angle and flow rate during the hemodialysis procedure are relatively unexplored. Since the flow field in the region of the venous needle may be a source of damage, in the current study, a numerical investigation of the effect of venous needle's angle and flow rate on hemodynamic parameters of the flow inside a hemodialysis graft has been carried out. Five cases of different needle angles and flow rates with graft flow rate of 500 ml/min have been investigated. Results indicate that in lower angle and lower flow rates the risk of damage is less because of lower wall shear stress and more uniform shear stress distribution on graft wall.

Effect of arteriovenous graft flow rate on vascular access hemodynamics in a novel modular anastomotic valve device

2018 ◽  
Vol 19 (5) ◽  
pp. 446-454 ◽  
Author(s):  
Andrew McNally ◽  
A George Akingba ◽  
Philippe Sucosky
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Rate ◽  
Vascular Access ◽  
Arteriovenous Graft ◽  
Oscillatory Shear Index ◽  
Flow Rates ◽  
Graft Flow ◽  
Relative Residence Time ◽  
Wall Shear

Purpose: Perturbed vascular access hemodynamics is considered a potential driver of intimal hyperplasia, the leading cause of vascular access failure. To improve vascular access patency, a modular anastomotic valve device has been designed to normalize venous flow between hemodialysis periods while providing normal vascular access during hemodialysis. The objective of this study was to quantify the effects of arteriovenous graft flow rate on modular anastomotic valve device vascular access hemodynamics under realistic hemodialysis conditions. Methods: Modular anastomotic valve device inlet and outlet flow conditions and velocity profiles were measured by ultrasound Doppler in a vascular access flow loop replicating arteriovenous graft flow rates of 800, 1000, and 1500 mL/min. Fluid–structure interaction simulations were performed to identify low wall shear stress regions on the vein wall and to characterize them in terms of temporal shear magnitude, oscillatory shear index, and relative residence time. The model was validated with respect to the Doppler measurements. Results: The low wall shear stress region generated downstream of the anastomosis under low and moderate arteriovenous graft flow rates was eliminated under the highest arteriovenous graft flow rate. Increase in arteriovenous graft flow rate from 800 to 1500 mL/min resulted in a substantial increase in wall shear stress magnitude (27-fold increase in temporal shear magnitude), the elimination of wall shear stress bidirectionality (0.20-point reduction in oscillatory shear index), and a reduction in flow stagnation (98% decrease in relative residence time). While the results suggest the ability of high arteriovenous graft flow rates to protect the venous wall from intimal hyperplasia–prone hemodynamics, they indicate their adverse impact on the degree of venous hemodynamic abnormality.

scholarly journals Hemodynamic Analysis on the Anastomosis Angle in Arteriovenous Graft Using Multiphase Blood Model

2021 ◽  
Vol 11 (17) ◽  
pp. 8160
Author(s):  
Ji Tae Kim ◽  
Hyangkyoung Kim ◽  
Hong Sun Ryou
Keyword(s):  
Computed Tomography ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Arteriovenous Graft ◽  
Venous Anastomosis ◽  
Vein Wall ◽  
High Wall Shear Stress ◽  
Anastomosis Site ◽  
Wall Shear ◽  
Tomography Data

Numerical analysis was performed for the effect of the venous anastomosis angle in a forearm arteriovenous graft for hemodialysis using a multiphase blood model. The geometry of the blood vessel was generated based on the patient-computed tomography data. The anastomosis angles were set at 15°, 30°, and 45°. The hematocrit was set at 34%, 45%, and 58%. The larger anastomosis angle, high wall shear stress area >11 Pa, increases to the side of the vein wall away from the anastomosis site. Further, the relatively low wall shear stress area, <3 Pa, occurs near the anastomosis site in larger anastomosis angles. Therefore, the effect of high wall shear stress has advantages in the vicinity of the anastomosis, as the anastomosis angle is larger, but disadvantages as the distance from the anastomosis increases. Moreover, patients with low hematocrit are advantageous for WSS area.

Quantifying Turbulent Wall Shear Stress in an Arteriovenous Graft Using Large Eddy Simulation

2012 ◽  
Author(s):  
L. D. Browne ◽  
P. Griffin ◽  
M. T. Walsh
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Secondary Patency ◽  
Arteriovenous Graft ◽  
Venous Anastomosis ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Shear ◽  
Turbulent Wall

Hemodialysis patients require a vascular access capable of accommodating the high blood flow rates required for effective dialysis treatment. The arteriovenous graft is one such access. However, this access type suffers from reduced one year primary & secondary patency rates of 59–90% and 50–82% respectively [1]. The main contributor to the failure of this access is stenosis via the development of intimal hyperplasia (IH) that predominately occurs at the venous anastomosis. It is hypothesized that the resulting transitional to turbulent flow regime within the venous anastomosis contributes to the development of IH. The aim of this study is to investigate the influence of this transitional to turbulent behavior on wall shear stress within the venous anastomosis via the use of large eddy simulation.

scholarly journals Induction of aneurysmogenic high positive wall shear stress gradient by wide angle at cerebral bifurcations, independent of flow rate

2019 ◽  
Vol 131 (2) ◽  
pp. 442-452 ◽  
Author(s):  
Alexandra Lauric ◽  
James E. Hippelheuser ◽  
Adel M. Malek
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Rate ◽  
Stress Gradient ◽  
Dependent Manner ◽  
Parent Vessel ◽  
Spatial Gradients ◽  
Bifurcation Angle ◽  
Wall Shear ◽  
Dynamics Simulations

OBJECTIVEEndothelium adapts to wall shear stress (WSS) and is functionally sensitive to positive (aneurysmogenic) and negative (protective) spatial WSS gradients (WSSG) in regions of accelerating and decelerating flow, respectively. Positive WSSG causes endothelial migration, apoptosis, and aneurysmal extracellular remodeling. Given the association of wide branching angles with aneurysm presence, the authors evaluated the effect of bifurcation geometry on local apical hemodynamics.METHODSComputational fluid dynamics simulations were performed on parametric bifurcation models with increasing angles having: 1) symmetrical geometry (bifurcation angle 60°–180°), 2) asymmetrical geometry (daughter angles 30°/60° and 30°/90°), and 3) curved parent vessel (bifurcation angles 60°–120°), all at baseline and double flow rate. Time-dependent and time-averaged apical WSS and WSSG were analyzed. Results were validated on patient-derived models.RESULTSNarrow symmetrical bifurcations are characterized by protective negative apical WSSG, with a switch to aneurysmogenic WSSG occurring at angles ≥ 85°. Asymmetrical bifurcations develop positive WSSG on the more obtuse daughter branch. A curved parent vessel leads to positive apical WSSG on the side corresponding to the outer curve. All simulations revealed wider apical area coverage by higher WSS and positive WSSG magnitudes, with increased bifurcation angle and higher flow rate. Flow rate did not affect the angle threshold of 85°, past which positive WSSG occurs. In curved models, high flow displaced the impingement area away from the apex, in a dynamic fashion and in an angle-dependent manner.CONCLUSIONSApical shear forces and spatial gradients are highly dependent on bifurcation and inflow vessel geometry. The development of aneurysmogenic positive WSSG as a function of angular geometry provides a mechanotransductive link for the association of wide bifurcations and aneurysm development. These results suggest therapeutic strategies aimed at altering underlying unfavorable geometry and deciphering the molecular endothelial response to shear gradients in a bid to disrupt the associated aneurysmal degeneration.

The Effect of Wall Distensibility on Flow in a Two-Dimensional End-to-Side Anastomosis

1994 ◽  
Vol 116 (3) ◽  
pp. 294-301 ◽  
Author(s):  
D. A. Steinman ◽  
C. Ross Ethier
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Intimal Hyperplasia ◽  
Bypass Graft ◽  
Numerical Approach ◽  
Flow Patterns ◽  
Temporal Variations ◽  
Model Studies ◽  
Wall Shear ◽  
Wall Distensibility

The development of intimal hyperplasia at the distal anastomosis is the major cause of long-term bypass graft failure. To evaluate the suspected role of hemodynamic factors in the pathogenesis of distal intimal hyperplasia, an understanding of anastomotic flow patterns is essential. Due to the complexity of arterial flow, model studies typically make simplifying assumptions, such as treating the artery and graft walls as rigid. In the present study this restriction is relaxed to consider the effects of vessel wall distensibility on anastomotic flow patterns. Flow was simulated in an idealized 2-D distensible end-to-side anastomosis model, using parameters appropriate for the distal circulation and assuming a purely elastic artery wall. A novel numerical approach was developed in which the wall velocities are solved simultaneously with the fluid and pressure fields, while the wall displacements are treated via an iterative update. Both the rigid and distensible cases indicated the presence of elevated temporal variations and low average magnitudes of wall shear stress at sites known to be susceptible to the development of intimal hyperplasia. At these same sites, large spatial gradients of wall shear stress were also noted. Comparison between distensible-walled and corresponding rigid-walled simulations showed moderate changes in wall shear stress at isolated locations, primarily the bed, toe and heel. For example, in the case of a distensible geometry and a physiologic pressure waveform, the heel experienced a 38 percent increase in cycle-averaged shear stress, with a corresponding 15 percent reduction in shear stress variability, both relative to the corresponding values in the rigid-walled case. However, other than at these isolated locations, only minor changes in overall wall shear stress patterns were observed. While the physiological implications of such changes in wall shear stress are not known, it is suspected that the effects of wall distensibility are less pronounced than those brought about by changes in arterial geometry and flow conditions.

Wall Shear Stress in Development Process of Aneurysm Around Anterior Communicating Artery

2004 ◽  
Author(s):  
Kenichi Umezawa ◽  
Akihiro Torisu ◽  
Susumu Kudo ◽  
Ryuhei Yamaguchi
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Steady Flow ◽  
Flow Rate ◽  
Development Process ◽  
Anterior Cerebral Artery ◽  
High Flow ◽  
Anterior Communicating Artery ◽  
Wall Shear ◽  
Small Aneurysm

In the present paper, the distribution of the wall shear stress around the apex of the anterior communicating artery (ACoA) in the development process of aneurysm has been studied in laminar steady flow. The anterior communicating artery composing the circle of Willis is one of the predilection sites where the cerebral aneurysm occurs frequently. Once the small aneurysm initiates around the apex in one anterior cerebral artery (ACA) with high flow rate, the distribution of the wall shear stress abruptly changes around the initial aneurysm. With the development of the aneurysm, the wall shear stress distinctly changes along the concaved surface of the aneurysm. The distribution of the wall shear stress in the development process of the aneurysm is physiologically discussed from the viewpoint of hemodynamics.

Effects of stenoses on non-Newtonian flow of blood in blood vessels

2015 ◽  
Vol 08 (01) ◽  
pp. 1550010 ◽  
Author(s):  
Om Prakash ◽  
O. D. Makinde ◽  
S. P. Singh ◽  
Nidhi Jain ◽  
Devendra Kumar
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Blood Vessels ◽  
Flow Rate ◽  
Homogeneous Fluid ◽  
Human Artery ◽  
Bingham Plastic ◽  
Uniform Cross Section ◽  
Flow Through ◽  
Wall Shear

In this paper, a mathematical model for steady blood flow through blood vessels with uniform cross-section in stenoses arteries has been proposed. Blood is assumed to be non-Newtonian, incompressible and homogeneous fluid. Blood in human artery is represented as Bingham plastic fluid. Expressions for flow rate, wall shear stress, and resistance to flow against stenoses size have been obtained. Obtained results indicate that stenoses size decreases the flow rate and increases the wall shear stress as well as resistance to flow.

NUMERICAL SIMULATION OF THE EFFECT OF VENOUS NEEDLE'S FLOW ON FLOW PARAMETERS OF HEMODIALYSIS GRAFT AND ITS HEMODYNAMIC CONSEQUENCES

2014 ◽  
Vol 26 (05) ◽  
pp. 1450057
Author(s):  
H. Niroomand-Oscuii ◽  
N. Meghdadi
Keyword(s):  
Shear Stress ◽  
Graft Failure ◽  
Cell Alignment ◽  
Venous Anastomosis ◽  
Graft Stenosis ◽  
Graft Flow ◽  
Inlet Conditions ◽  
The Individual ◽  
Stage Renal Disease ◽  
Hemodialysis Graft

Arterio-Venous (AV) grafts which are used for hemodialysis, frequently develop intimal hyperplasia (IH) in venous anastomosis and ultimately leads to graft failure which is the major cause of morbidity and mortality in patients with the end stage renal disease (ESRD). Although the high AV access blood flow has been implicated in the pathogenesis of graft stenosis, the potential role of needle turbulence during hemodialysis is relatively unexplored. In the current study, a numerical survey is carried out to investigate the effect of venous needle's flow on hemodynamic parameters of the flow inside a hemodialysis graft. Two cases include the individual graft flow and the graft flow combined with a needle flow which both of them are evaluated and their results are compared to the cell morphology are represented in this research. Blood is considered as an incompressible Newtonian fluid with density of 1050 [Kg/(m3)] and dynamic viscosity of 0.0035 [Pa.s] and the graft was considered as a rigid vessel due to its low compliance. Flow rates were considered 500 and 100 [mL/min] as inlet conditions of the graft and the needle, respectively. Results show that the presence of the needle's flow causes to increase the amount of shear stress and nonuniformity of the shear stress distribution on the graft wall, where the cell alignment is lost in the presence of needle flow. These findings suggest the presence of potential relationship between venous needle flow during hemodialysis and endothelial dysfunction which may lead to vascular injury and graft failure.

scholarly journals Analysis of Flow Characteristics of the Blood Flowing through an Inclined Tapered Porous Artery with Mild Stenosis under the Influence of an Inclined Magnetic Field

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Neetu Srivastava
Keyword(s):  
Magnetic Field ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Volumetric Flow Rate ◽  
Mhd Equations ◽  
Inclined Magnetic Field ◽  
Wall Shear

Analytical investigation of MHD blood flow in a porous inclined stenotic artery under the influence of the inclined magnetic field has been done. Blood is considered as an electrically conducting Newtonian fluid. The physics of the problem is described by the usual MHD equations along with appropriate boundary conditions. The flow governing equations are finally transformed to nonhomogeneous second-order ordinary differential equations. This model is consistent with the principles of magnetohydrodynamics. Analytical expressions for the velocity profile, volumetric flow rate, wall shear stress, and pressure gradient have been derived. Blood flow characteristics are computed for a specific set of values of the different parameters involved in the model analysis and are presented graphically. Some of the obtained results show that the flow patterns in converging region (ξ<0), diverging region (ξ>0), and nontapered region (ξ=0) are effectively influenced by the presence of magnetic field and change in inclination of artery as well as magnetic field. There is also a significant effect of permeability on the wall shear stress as well as volumetric flow rate.

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