On the Calculation of Fluid Shear Stresses at the Wall of Dilated Large Arteries: Part II—Application to 3D Computational Models

2000 ◽  
Author(s):  
Ender A. Finol ◽  
Cristina H. Amon
Keyword(s):  
Blood Flow ◽  
Stress Tensor ◽  
Computational Models ◽  
Numerical Study ◽  
Aortic Aneurysms ◽  
Shear Stresses ◽  
Numerical Predictions ◽  
Aneurysm Wall ◽  
Pulsatile Flows ◽  
Wall Shear

Abstract Experimental and numerical investigations of pulsatile flows in artery models have been numerous during the last two decades. For 3D artery models, numerical predictions of wall shear stresses can be rather difficult to make due to the six independent stress tensor components that may be evaluated at any particular time during the blood flow pulse. The only 3D numerical study of blood flow in Abdominal Aortic Aneurysms (AAAs) known to the authors is that of Taylor and Yamaguchi (1994), in which iso-shear stress contours are reported for an asymmetric aneurysm model. However, the projection of these stresses at the aneurysm wall is not reported. This paper presents an extension of the plane stress formulation outlined in Part I, combined with a transformation of the stress tensor, as an alternative procedure for the calculation of wall shear stresses in 3D dilated artery models, with application to asymmetric aneurysms.

Numerical study of hemodynamics after stent implantation during the cardiac cycle

2021 ◽  
Vol 15 (2) ◽  
pp. 8016-8028
Author(s):  
Abdelhakem Belaghit ◽  
B. Aour ◽  
M. Larabi ◽  
A. A. Tadjeddine ◽  
S. Mebarki
Keyword(s):  
Blood Flow ◽  
Stent Implantation ◽  
Cardiac Cycle ◽  
Numerical Study ◽  
Shear Stresses ◽  
Flow Profile ◽  
Hemodynamic State ◽  
Dynamics Simulations ◽  
Medical Planning

The descending aortic aneurysm is one of the most catastrophic cardiovascular emergencies resulting in high mortality worldwide. Clinical observations have pointed out that stent implantation in the sick aorta should probably allow stabilization of the hemodynamic state of the patient's aorta. To better understand the hemodynamic impact of a stent-treated aneurysm, numerical simulations are used to evaluate hemodynamic parameters. These latter including flow profile, velocity distribution, aortic wall pressure and shear stress, which are difficult to measure in vivo. It should be noted that the numerical modeling assists in medical planning by providing patterns of blood circulation, in particular, the distribution of pressures and shear stresses in the wall. In this context, the pulsatile blood flow in the aneurysmal aorta with stent is studied by CFD (Computational Fluid Dynamics) simulations. Realistic boundary conditions time dependent are prescribed at the level of the different arteries of the complete aorta models. The hemodynamic profile of the aneurysmal aorta with stent was analyzed by contour planes of velocity vectors, pressures and shear stresses at different times during the cardiac cycle. The obtained results made it possible to show the effect of the stent on the improvement of the blood flow by solving the problems of hemodynamic disturbances in the aorta.  The methodology used in this work has revealed detailed and necessary information for the cases studied and shows the interest of the numerical tool for diagnosis and surgery.

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.

Numerical Study on the Pulsatile Flow Characteristics of Proximal Anastomotic Models

2005 ◽  
Vol 219 (5) ◽  
pp. 361-379 ◽  
Author(s):  
L P Chua ◽  
J-M Zhang ◽  
S C M Yu ◽  
D N Ghista ◽  
Y S Tan
Keyword(s):  
Flow Separation ◽  
Patency Rate ◽  
Numerical Study ◽  
Flow Characteristics ◽  
High Time ◽  
Shear Stresses ◽  
Proximal Anastomosis ◽  
Haemodynamic Parameters ◽  
Simulation Results ◽  
Wall Shear

Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45° forward facing, 45° backward facing, and 90° anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45° forward facing to 45° backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45° backward facing and 90° grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results obtained were consistent with those of experimental measurements. Based on the validated simulation results, the 45° backward-facing graft was found to have the lowest variation range of time-averaged WSS and the lowest segmental average of WSSG among the three models investigated. The 45° backward-facing graft is thus recommended for the bypass operation with expected higher patency rate.

Computational Modeling of Shear-Based Hemolysis Caused by Renal Obstruction

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Polina A. Segalova ◽  
K. T. Venkateswara Rao ◽  
Christopher K. Zarins ◽  
Charles A. Taylor
Keyword(s):  
Blood Flow ◽  
Boundary Conditions ◽  
Renal Artery ◽  
Aortic Aneurysms ◽  
Cfd Modeling ◽  
Patient Specific ◽  
Shear Stresses ◽  
Baseline Model ◽  
Implantable Medical Devices ◽  
Renal Obstruction

As endovascular treatment of abdominal aortic aneurysms (AAAs) gains popularity, it is becoming possible to treat certain challenging aneurysmal anatomies with endografts relying on suprarenal fixation. In such anatomies, the bare struts of the device may be placed across the renal artery ostia, causing partial obstruction to renal artery blood flow. Computational fluid dynamics (CFD) was used to simulate blood flow from the aorta to the renal arteries, utilizing patient-specific boundary conditions, in three patient models and calculate the degree of shear-based blood damage (hemolysis). We used contrast-enhanced computed tomography angiography (CTA) data from three AAA patients who were treated with a novel endograft to build patient-specific models. For each of the three patients, we constructed a baseline model and endoframe model. The baseline model was a direct representation of the patient’s 30-day post-operative CTA data. This model was then altered to create the endoframe model, which included a ring of metallic struts across the renal artery ostia. CFD was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, shear stresses, and the normalized index of hemolysis (NIH) were quantified for all patients. The overall differences between the baseline and endoframe models for all three patients were minimal, as measured though pressure, volumetric flow, velocity, and shear stress. The average NIH across the three baseline and endoframe models was 0.002 and 0.004, respectively. Results of CFD modeling show that the overall disturbance to flow caused by the presence of the endoframe struts is minimal. The magnitude of the NIH in all models was well below the accepted design and safety threshold for implantable medical devices that interact with blood flow.

scholarly journals The effect to flow rate characteristic on biodegradation of bone scaffold

2017 ◽  
Vol 13 (4-2) ◽  
pp. 546-552 ◽  
Author(s):  
Hasan Basri ◽  
Jimmy Deswidawansyah Nasution ◽  
Ardiyansyah Syahrom ◽  
Mohd Ayub Sulong ◽  
Amir Putra Md. Saad ◽  
...  
Keyword(s):  
Shear Stress ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Computational Models ◽  
Shear Stresses ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Pressure Drops ◽  
Bone Scaffolds ◽  
Wall Shear

This paper proposes an improved modeling approach for bone scaffolds biodegradation. In this study, the numerical analysis procedure and computer-based simulation were performed for the bone scaffolds with varying porosities in determining the wall shear stresses and the permeabilities along with their influences on the scaffolds biodegradation process while the bio-fluids flow through within followed with the change in the flow rates. Based on the experimental study by immersion testing from 0 to 72 hours of the time period, the specimens with different morphologies of the commercial bone scaffolds were collected into three groups samples of 30%, 41%, and 55% porosities. As the representative of the cancellous bone morphology, the morphological degradation was observed by using 3-D CAD scaffold models based on microcomputed tomography images. By applying the boundary conditions to the computational fluid dynamics (CFD) and the fluid-structure interaction (FSI) models, the wall shear stresses within the scaffolds due to fluid flow rates variation had been simulated and determined before and after degradation. The increase of fluid flow rates tends to raise the pressure drop for scaffold models with porosities lower than 50% before degradation. As the porosities increases, the pressure drop decreases with an increase in permeability within the scaffold. The flow rates have significant effects on scaffolds with higher pressure drops by introducing the wall shear stresses with the highest values and lower permeability. These findings indicate the importance of using accurate computational models to estimate shear stress and determine experimental conditions in perfusion bioreactors for tissue engineering more accurate results will be achieved to indicate the natural distributions of fluid flow velocity, wall shear stress, and pressure.

Blood Flow Manipulation in the Aorta With Coarctation and Arch Narrowing for Pediatric Subjects

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Yuxi Jia ◽  
Kumaradevan Punithakumar ◽  
Michelle Noga ◽  
Arman Hemmati
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Arch ◽  
Flow Direction ◽  
Upper Body ◽  
Patient Specific ◽  
Shear Stresses ◽  
Wall Shear

Abstract The characteristics of blood flow in an abnormal pediatric aorta with an aortic coarctation and aortic arch narrowing are examined using direct numerical simulations and patient-specific boundary conditions. The blood flow simulations of a normal pediatric aorta are used for comparison to identify unique flow features resulting from the aorta geometrical anomalies. Despite flow similarities compared to the flow in normal aortic arch, the flow velocity decreases with an increase in pressure, wall shear stress, and vorticity around both anomalies. The presence of wall shear stresses in the trailing indentation region and aorta coarctation opposing the primary flow direction suggests that there exist recirculation zones in the aorta. The discrepancy in relative flowrates through the top and bottom of the aorta outlets, and the pressure drop across the coarctation, implies a high blood pressure in the upper body and a low blood pressure in the lower body. We propose using flow manipulators prior to the aortic arch and coarctation to lower the wall shear stress, while making the recirculation regions both smaller and weaker. The flow manipulators form a guide to divert and correct blood flow in critical regions of the aorta with anomalies.

Reduced Effect of Aspirin on Thrombus Formation at High Shear and Disturbed Laminar Blood Flow

1996 ◽  
Vol 75 (05) ◽  
pp. 827-832 ◽  
Author(s):  
R Marius Barstad ◽  
Una Ørvim ◽  
Maria J A.G Hamers ◽  
Geir E Tjønnfjord ◽  
Frank R Brosstad ◽  
...  
Keyword(s):  
Blood Flow ◽  
Thrombus Formation ◽  
Secondary Prophylaxis ◽  
Significant Inhibition ◽  
Von Willebrand Disease ◽  
Shear Stresses ◽  
High Shear ◽  
Cross Sectional ◽  
Wall Shear ◽  
Von Willebrand

SummaryAspirin is the most commonly used antithrombotic drug in primary and secondary prophylaxis against cardio- and cerebrovascular disease. In previous studies from our laboratory it was demonstrated that the effect of aspirin on collagen-induced thrombus formation in a parallelplate perfusion device with laminar blood flow is shear rate dependent. Although aspirin did not affect collagen-induced thrombus formation at 650 s-1 (medium sized arteries), a significant inhibition of thrombus formation by approximately 38% at 2,600 s-1 (moderately stenoses in medium sized arteries) was observed. At present we have extended these studies to thrombus formation at the apex of eccentric stenoses in a parallel-plate perfusion chamber device. The stenoses reduced the cross-sectional area of the blood flow channel of the perfusion chambers by 60 or 80%, introducing disturbed laminar flow and apex wall shear rates of 2,600 and 10,500 s-1, respectively. The corresponding wall shear stresses were 80 and 315 dynes/cm2, respectively.Aspirin reduced the platelet thrombus volume at the 60% stenosis by 45% (p <0.03), and the fibrin deposition by 70% (p <0.004). However, none of these parameters were affected by aspirin at the 80% stenosis. These observations may at least partly explain why aspirin has a limited clinical effect in preventing arterial thrombus formation in atherosclerotic vessels at high shear and disturbed blood flow. In contrast, thrombus formation in blood from one patient with Glanzmann’s thrombasthenia and two patients with von Willebrand disease subtype 2M was almost abolished at this blood flow condition. Thus, blocking the function of either von Willebrand factor or glycoprotein IIb/IIIa may represent better antithrombotic approaches for such critical events than blocking the prostaglandin metabolism by aspirin. The lack of effect of aspirin on thrombus formation at the 80% stenosis may reflect shear-induced platelet activation at the stenosis inlet region, since shear-induced platelet aggregation in rotational viscometers is not affected by aspirin at shear stresses exceeding 100 dynes/cm2.

In-vivo blood flow parameters can predict at-risk aortic aneurysms and dissection: a comprehensive biomechanics model

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
M Salmasi ◽  
O.A Jarral ◽  
S Pirola ◽  
S Sasidharan ◽  
J Pepper ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Risk Prediction ◽  
Aortic Wall ◽  
Tissue Mechanics ◽  
Aortic Aneurysms ◽  
Funding Source ◽  
Wall Shear

Abstract Background Abnormal blood flow patterns can alter the material properties of the thoracic aorta via altered vascular biology and tissue biomechanics. In-vivo haemodynamic assessment of the aorta is yet to penetrate clinical practice due to our limited understanding of its effect on aortic wall properties. The decision for surgical treatment is based on size thresholds, limited to a single measurement of aortic diameter from routine imaging, although many aortic dissections (40–60%) occur below these size thresholds. This multi-centre study aims to assess the clinical utility of biomechanics principles in thoracic aortic aneurysm (TAA) risk rupture prediction using a substantial sample size. Methods Fifty-five patients undergoing surgery for root or ascending TAA were recruited from five cardiac centres. Bicuspid aortic valves and connective tissue disease were excluded from this study.Haemodynamic assessment Pre-operative 4-dimensional flow magnetic resonance imaging (4D-MRI) were conducted. Direct 4D-flow analysis and computational fluid dynamics (CFD) were performed creating detailed wall shear stress (WSS) maps across the whole aneurysms. Aortic wall assessment The aneurysmal aortic sample was obtained from surgery and subjected to region specific uniaxial failure tests in the circumferential and longitudinal directions, as well as delamination testing within the aortic media. Whole aneurysm histological characterisation was also conducted using computational pathology techniques. Blood flow, tissue mechanics and microstructural properties were used to develop a risk prediction model with assessment of elastin, collagen and smooth muscle cell composition, as well as failure strain assessment and dissection energy function. Results Outcomes of mechanical properties were: Young's Elastic Modulus as a measure of aortic stiffness (0.85 MPa ±0.69), as well as maximal tensile strength (0.49 MPa ± 0.36), which demonstrated reduced aortic wall strength in the outer curvature. This correlated with increased wall shear stress (WSS) (up to 10 Pa) and flow velocity (up to 43 l/min). Regions of abnormal flow and tissue mechanics correlated significantly with degraded medial microstructure (elastin abundance: 34 vs 66%; collagen abundance 26 vs 57%, p&lt;0.05). Conclusions CFD modelling has the potential to provide a risk prediction of acute events in TAA beyond the current size classification, as validated by altered aortic tissue properties. Future longitudinal studies are warranted to validate this methods in moderately enlarging thoracic aortas. Flow, mechanical, histology properties Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): NIHR Imperial College BRC

Effects of blood flow characteristics on rupture of cerebral aneurysm: Computational study

2021 ◽  
pp. 2150143
Author(s):  
Xiao-Yong Shen ◽  
M. Barzegar Gerdroodbary ◽  
Amin Poozesh ◽  
Amir Musa Abazari ◽  
S. Misagh Imani
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
High Risk ◽  
Wall Shear Stress ◽  
Flow Pattern ◽  
Cerebral Aneurysm ◽  
Computational Study ◽  
Fluid Dynamic ◽  
Aneurysm Wall ◽  
Wall Shear

In recent decades, cardiovascular disease and stroke are recognized as the most important reason for the high death rate. Irregular bloodstream and the circulatory system are the main reason for this issue. In this paper, Computational Fluid dynamic method is employed to study the impacts of the flow pattern inside the cerebral aneurysm for detection of the hemorrhage of the aneurysm. To achieve a reliable outcome, blood flow is considered as a non-Newtonian fluid with a power-law model. In this study, the influence of the blood viscosity and velocity on the pressure distribution and average wall shear stress (AWSS) are comprehensively studied. Moreover, the flow pattern inside the aneurysm is investigated to obtain the high-risk regions for the rupture of the aneurysm. Our results indicate that the wall shear stress (WSS) increases with increasing blood flow velocity. Furthermore, the risk of aneurysm rupture is considerably increased when the AWSS increases more than 0.6. Indeed, the blood flow with high viscosity expands the high-risk region on the wall of the aneurysm. Blood flow indicates that the angle of the incoming bloodstream is substantially effective in the high-risk region on the aneurysm wall. The augmentation of the blood velocity and vortices considerably increases the risk of hemorrhage of the aneurysm.

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