Pressure Induced Strain at Femoral Artery Bypass Graft Junctions

2007 ◽  
Author(s):  
Triona Campbell ◽  
Reena Cole ◽  
Michael O’Donnell
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Arterial Disease ◽  
Shear Stresses ◽  
Artery Bypass Graft ◽  
Short Period ◽  
Wall Shear ◽  
Hydrodynamic Stresses

Femoral or femoropopliteal artery bypass graft junctions have a predilection for failure due to restenosis. It has been clinically proven that vascular reconstructions tend to restenose within a short period of time [1]. Extensive studies have cited wall shear stresses as being primarily responsible and definite correlations between hydrodynamic stresses in the arterial wall and arterial disease have been shown [2,3]. However intensive investigations into wall shear stresses have lead to conflicting arguments on the proliferation and propagation of stenoses. It was concluded by Freidman [4] that the intima at sites exposed to relatively high or unidirectional shears thickened initially, but as time progressed the greatest thicknesses were ultimately achieved at sites exposed to lower or more oscillatory shear environments. A contradicting view was expressed by Nazemi [5] that low wall shear stress contributed to the onset of atherosclerotic plaque formation, whilst high wall shear stress encouraging plaque growth. A number of studies have however established a statistically significant correlation between pressure and intimal hyperplasia and concluded that blood pressure and not blood flow is the primary factor responsible for the localization of atherosclerosis [6–8].

Preliminary Near Wall Hemodynamic Evaluation of a Coronary Artery Bypass Graft Model With a Flow Streamlining Implant

2002 ◽  
Author(s):  
Pedro D. Pedroso ◽  
Andreas S. Anayiotos ◽  
Brad L. Hershey ◽  
Evangelos Eleftheriou ◽  
William L. Holman
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Wall Shear Stress ◽  
Coronary Artery Bypass Graft ◽  
Coronary Artery Bypass ◽  
Saphenous Vein ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Artery Bypass Graft ◽  
Wall Shear

Coronary artery disease (CAD) is the leading cause of death in the world today. According to the American Heart Association 529,659 people in 1999 died as a result of CAD [1]. Starting in the 1960’s, surgeons have used Coronary Artery Bypass Graft (CABG) techniques in order to reestablish blood flow to the heart. Today, the procedure remains the same, using autologous grafts, such as the mammary artery and the saphenous vein. An unresolved problem, is that a significant number of CABGs reocclude months to years postoperatively. In the case of Saphenous Vein Grafts (SVGs) typically 50% of these bypasses are totally occluded months to years after the procedure, the remaining half being more than 50% occluded [2]. The re-occlusion of CABGs is due to a process labeled intimal hyperplasia (IH). Investigators have shown that IH, believed by some to be a remodeling process, occurs at branch sites, regions of curvature, and anastomotic junctions [3,4]. At these sites there are low residence times, slow secondary structures, disturbed flow, and areas of recirculation, therefore the onset of IH is believed to be hemodynamically linked. Most recently, floor IH has been attributed to four variables: time averaged wall shear stress (WSS), oscillating shear index (OSI), spatial wall shear stress gradients (WSSG), and temporal WSSG [5]. Adverse values of these parameters, in the case of SVGs, are believed to be caused by impedance mismatch at the anastomosis site. Over time this characteristic causes a bulge at the sinus. Such a morphology additionally contributes to disturbed flows which tend to propagate down the CABG and are believed to play a major role in the development of IH and the eventual failure of the graft.

Characterizing Flow in the Vertebro-Basilar System Using MR in Conjunction With Subject-Specific Computational Models

2010 ◽  
Author(s):  
Amanda K. Wake ◽  
John C. Gore ◽  
J. Christopher Gatenby
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vascular Graft ◽  
Graft Failure ◽  
Computational Models ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Arterial Graft ◽  
Vessel Patency ◽  
Wall Shear

Coronary artery bypass graft failure is often a consequence of intimal hyperplasia (IH), which correlates with hemodynamic factors (e.g., wall shear stress); this relationship has been used to evaluate arterial graft design [e.g., 1–4]. The vertebro-basilar system is a native arterial merge (i.e., two arteries, the vertebrals, converge into a single artery, the basilar artery); thus, characterizing the flow field of this system in healthy subjects could be useful for early detection of anomalies (e.g., aneurysms) or for vascular graft design improvements to ensure graft/vessel patency. This study uses high field MR and phase contrast MR (PCMR) to investigate the hemodynamics of the vertebro-basilar system in a healthy, adult subject for predicting pathophysiologically-relevant flow patterns (e.g., low wall shear stress) that are related to IH and subsequent graft failure.

A Computational Technique for Robust Optimization of Cardiovascular Bypass Graft Surgeries

2010 ◽  
Author(s):  
Sethuraman Sankaran ◽  
Alison L. Marsden
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Operative Mortality ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Computational Technique ◽  
First Year ◽  
Synthetic Material ◽  
Plaque Deposition ◽  
Wall Shear

Bypass graft (BG) surgeries involve surgical construction of a graft over a blocked blood vessel. The graft can either be native tissue of the patient or a synthetic material. Some commonly performed BG surgeries include aorto-bifemoral, femoro-popliteal, femoro-tibial, and coronary artery bypass (CABG). The operative mortality rate for CABG is around 3%. Around 15 to 30% of bypass grafts occlude within the first year of surgery, increasing to over 50% after 10 years. Graft incompatibility, and hemodynamic factors such as blood recirculation, low wall shear stress, and abnormal wall shear stress gradients play an important role in the onset and development of intimal thickening and plaque deposition (atherogenesis).

scholarly journals Impact of Competitive Flow on Hemodynamics in Coronary Surgery: Numerical Study of ITA-LAD Model

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Jinli Ding ◽  
Youjun Liu ◽  
Feng Wang ◽  
Fan Bai
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Wall Shear Stress ◽  
Numerical Study ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Coronary Bypass ◽  
Coronary Artery Bypass Grafts ◽  
Wall Shear ◽  
The Impact

Competitive flow from native coronary artery is considered as a major factor in the failure of the coronary artery bypass grafts. However, the physiological effects are not very clear. The aim is to research the impact of competitive flow caused by different left anterior descending (LAD) artery stenosis degrees on hemodynamics in internal thoracic artery (ITA) bypass graft. An idealized ITA-LAD model was built in CAD tools. The degree of the competitive flow was divided into five classes according to different LAD stenosis degrees: higher (no stenosis), secondary (30% stenosis), reduced (50% stenosis), lower (75% stenosis) and no competitive flow (fully stenosis). Finite volume method was employed for the numerical simulation. The flow velocity distributions, wall shear stress and oscillatory shear index were analyzed. Results showed that higher competitive flow in the bypass graft would produce unbeneficial wall shear stress distribution associating with endothelial dysfunction and subsequent graft failure. The coronary bypass graft surgery was preferred to be carried out when the LAD stenosis was higher than 75%.

Preston-Static Tubes for the Measurement of Wall Shear Stress

1994 ◽  
Vol 116 (3) ◽  
pp. 645-649 ◽  
Author(s):  
Josef Daniel Ackerman ◽  
Louis Wong ◽  
C. Ross Ethier ◽  
D. Grant Allen ◽  
Jan K. Spelt
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Convenient Method ◽  
Pipe Flow ◽  
Total Pressure ◽  
Static Pressure ◽  
Shear Stresses ◽  
Streamline Curvature ◽  
Syringe Needle ◽  
Wall Shear

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Requirements for Mesh Resolution in 3D Computational Hemodynamics

2000 ◽  
Vol 123 (2) ◽  
pp. 134-144 ◽  
Author(s):  
Sujata Prakash ◽  
C. Ross Ethier
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Velocity Fields ◽  
Shear Stresses ◽  
Large Artery ◽  
Mesh Independence ◽  
Wall Shear

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features. Here we examine, for a single arterial geometry, how velocity and wall shear stress patterns depend on mesh characteristics. A well-validated Navier-Stokes solver was used to simulate flow in an anatomically realistic human right coronary artery (RCA) using unstructured high-order tetrahedral finite element meshes. Velocities, wall shear stresses (WSS), and wall shear stress gradients were computed on a conventional “high-resolution” mesh series (60,000 to 160,000 velocity nodes) generated with a commercial meshing package. Similar calculations were then performed in a series of meshes generated through an adaptive mesh refinement (AMR) methodology. Mesh-independent velocity fields were not very difficult to obtain for both the conventional and adaptive mesh series. However, wall shear stress fields, and, in particular, wall shear stress gradient fields, were much more difficult to accurately resolve. The conventional (nonadaptive) mesh series did not show a consistent trend towards mesh-independence of WSS results. For the adaptive series, it required approximately 190,000 velocity nodes to reach an r.m.s. error in normalized WSS of less than 10 percent. Achieving mesh-independence in computed WSS fields requires a surprisingly large number of nodes, and is best approached through a systematic solution-adaptive mesh refinement technique. Calculations of WSS, and particularly WSS gradients, show appreciable errors even on meshes that appear to produce mesh-independent velocity fields.

scholarly journals Assessing Bioinspired Topographies for their Antifouling Potential Control Using Computational Fluid Dynamics (CFD)

2018 ◽  
Vol 152 ◽  
pp. 02004 ◽  
Author(s):  
Jacky Ling ◽  
Felicia Wong Yen Myan
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Extended Period ◽  
Slip Boundary Condition ◽  
Shear Stresses ◽  
Cfd Simulations ◽  
Potential Control ◽  
Slip Boundary ◽  
Computational Fluid Dynamics Cfd ◽  
Wall Shear

Biofouling is the accumulation of unwanted material on surfaces submerged or semi submerged over an extended period. This study investigates the antifouling performance of a new bioinspired topography design. A shark riblets inspired topography was designed with Solidworks and CFD simulations were antifouling performance. The study focuses on the fluid flow velocity, the wall shear stress and the appearance of vortices are to be noted to determine the possible locations biofouling would most probably occur. The inlet mass flow rate is 0.01 kgs-1 and a no-slip boundary condition was applied to the walls of the fluid domain. Simulations indicate that Velocity around the topography averaged at 7.213 x 10-3 ms-1. However, vortices were observed between the gaps. High wall shear stress is observed at the peak of each topography. In contrast, wall shear stress is significantly low at the bed of the topography. This suggests the potential location for the accumulation of biofouling. Results show that bioinspired antifouling topography can be improved by reducing the frequency of gaps between features. Linear surfaces on the topography should also be minimized. This increases the avenues of flow for the fluid, thus potentially increasing shear stresses with surrounding fluid leading to better antifouling performance.

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.

scholarly journals Numerical Simulation of Dispersed Particle-Blood Flow in the Stenosed Coronary Arteries

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Mongkol Kaewbumrung ◽  
Somsak Orankitjaroen ◽  
Pichit Boonkrong ◽  
Buraskorn Nuntadilok ◽  
Benchawan Wiwatanapataphee
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Shear Stress ◽  
Coronary Artery ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Stokes Equations ◽  
Spherical Shape ◽  
Shear Stresses ◽  
Wall Shear

A mathematical model of dispersed bioparticle-blood flow through the stenosed coronary artery under the pulsatile boundary conditions is proposed. Blood is assumed to be an incompressible non-Newtonian fluid and its flow is considered as turbulence described by the Reynolds-averaged Navier-Stokes equations. Bioparticles are assumed to be spherical shape with the same density as blood, and their translation and rotational motions are governed by Newtonian equations. Impact of particle movement on the blood velocity, the pressure distribution, and the wall shear stress distribution in three different severity degrees of stenosis including 25%, 50%, and 75% are investigated through the numerical simulation using ANSYS 18.2. Increasing degree of stenosis severity results in higher values of the pressure drop and wall shear stresses. The higher level of bioparticle motion directly varies with the pressure drop and wall shear stress. The area of coronary artery with higher density of bioparticles also presents the higher wall shear stress.

Stress Distributions Along the Inner Wall of the Femoropopliteal Bypass Graft Anastomoses

2004 ◽  
Author(s):  
Triona Campbell ◽  
Reena Cole ◽  
Mark Davies ◽  
Michael O’Donnell
Keyword(s):  
Significant Role ◽  
Atherosclerotic Plaque ◽  
Numerical Models ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Shear Stresses ◽  
Stress Distributions ◽  
Femoropopliteal Bypass ◽  
Artery Bypass Graft ◽  
Femoropopliteal Artery

The distal junction of a femoral or femoropopliteal artery bypass graft has a predilection for failure due to restenosis. However neither the initiation nor proliferation process of atherosclerotic plaque is completely understood. Presently it is hypothesized that the process of atherosclerosis initiates as a result of damage or ‘insult’ to the endothelium. The cause of this initial damage is unknown, although it is widely believed that wall shear stresses are a contributing factor. The primary cause of plaque proliferation has not yet been identified, however it is our belief that intramural pressure plays a significant role. In this study numerical models of the proximal and distal junctions were used to determine both the location and magnitude of the stresses caused by intramural pressure. The simulated artery bypass graft was examined under both static and dynamic conditions.

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