Characterization and estimation of turbulence-related wall shear stress in patient-specific pulsatile blood flow

2019 ◽  
Vol 85 ◽  
pp. 108-117 ◽  
Author(s):  
Magnus Andersson ◽  
Tino Ebbers ◽  
Matts Karlsson
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Patient Specific ◽  
Pulsatile Blood Flow ◽  
Wall Shear

Computational Fluid Dynamics of a Vascular Access Case for Hemodialysis

2000 ◽  
Vol 123 (3) ◽  
pp. 284-292 ◽  
Author(s):  
Bogdan Ene-Iordache ◽  
Lidia Mosconi ◽  
Giuseppe Remuzzi ◽  
Andrea Remuzzi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Radial Artery ◽  
Stress Gradient ◽  
Vascular Lesions ◽  
Patient Specific ◽  
Wall Shear

Vascular accesses (VA) for hemodialysis are usually created by native arteriovenous fistulas (AVF) or synthetic grafts. Maintaining patency of VA continues to be a major problem for patients with end-stage renal disease, since in these vessels thrombosis and intimal hyperplasia often occur. These lesions are frequently associated with disturbed flow that develops near bifurcations or sharp curvatures. We explored the possibility of investigating blood flow dynamics in a patient-specific model of end-to-end native AVF using computational fluid dynamics (CFD). Using digital subtraction angiographies of an AVF, we generated a three-dimensional meshwork for numerical analysis of blood flow. As input condition, a time-dependent blood waveform in the radial artery was derived from centerline velocity obtained during echo-color-Doppler ultrasound examination. The finite element solution was calculated using a fluid-dynamic software package. In the straight, afferent side of the radial artery wall shear stress ranged between 20 and 36 dynes/cm2, while on the inner surface of the bending zone it increased up to 350 dynes/cm2. On the venous side, proximal to the anastomosis, wall shear stress was oscillating between negative and positive values (from −12 dynes/cm2 to 112 dynes/cm2), while distal from the anastomosis, the wall shear stress returned within the physiologic range, ranging from 8 to 22 dynes/cm2. Areas of the vessel wall with very high shear stress gradient were identified on the bending zone of the radial artery and on the venous side, after the arteriovenous shunt. Secondary blood flows were also observed in these regions. CFD gave a detailed description of blood flow field and showed that this approach can be used for patient-specific analysis of blood vessels, to understand better the role of local hemodynamic conditions in the development of vascular lesions.

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.

The Effect of Asymmetry in Abdominal Aortic Aneurysms Under Physiologically Realistic Pulsatile Flow Conditions

2003 ◽  
Vol 125 (2) ◽  
pp. 207-217 ◽  
Author(s):  
E. A. Finol ◽  
K. Keyhani ◽  
C. H. Amon
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pulsatile Flow ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Aortic Aneurysms ◽  
Pulsatile Blood Flow ◽  
Abdominal Aortic ◽  
Wall Shear

In the abdominal segment of the human aorta under a patient’s average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50⩽Rem⩽300, corresponding to a range of peak Reynolds numbers 262.5⩽Repeak⩽1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.

ESTIMATION OF WALL SHEAR STRESS OF COMPLIANT THORACIC AORTA WITH ANEURYSM

2020 ◽  
Vol 20 (03) ◽  
pp. 2050013
Author(s):  
AHMED BAKHIT ALANAZI ◽  
MOHAMED YACIN SIKKANDAR ◽  
MOHAMED IBRAHIM WALY
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Pattern ◽  
Thoracic Aorta ◽  
Mass Flow ◽  
Tangential Force ◽  
Patient Specific ◽  
Hemodynamic Pattern ◽  
Wall Shear

In this paper, a numerical estimation of wall shear stress (WSS) in a compliant Thoracic Aorta (TA) with aneurysm is modeled and the hemodynamic pattern is studied using Computational Fluid Dynamics (CFD). Thoracic Aortic Aneurysm (TAA) is an excessively localized enlargement of TA caused by weakness in the arterial wall and it can rupture the inner wall intima and continue on to the outer wall adventitia. WSS is a tangential force exerted by blood flow on the vessel wall, and its estimation is clinically very important because any change in WSS is considered as a vital cue in the onset of aneurysm. In this work, a three-dimensional (3D) model of a TAA reconstructed from computed tomography (CT) images comprising of 600 slices with 1-mm resolution from neck to hip is considered and patient-specific simulations have been carried out in compliant TA under rest and exercise conditions. The findings show that the change in wall geometry was marginal due to variation in pressure forces inside and is not the primary source for expansion of an aneurysm. It was inferred that expansion was rather due to thinning of the wall, owing to damage caused to the inner lining of the tissues, at regions of high WSS. It was found that the geometry extraction is important as any change in length causes a corresponding variation in mass flow through it. Although mass conservation is maintained irrespective of the length, it does affect the rate of flow due to shifting in the pressure boundary conditions with the length as it varies the pressure inside the system. Modeling of the geometry is very important as the change in mass flow will affect the outlet velocity and strength of vortices. Surprisingly, the split-up of flow is consistent but the geometric change in the model has no effect on WSS values and flow pattern. The results of this study provide important information such as blood flow pattern and pressure drops in the compliant TA on WSS estimations with TAA diseases.

scholarly journals Asymmetric distribution of pathogenic low wall shear stress of the bilateral subclavian arteries: two case reports

2021 ◽  
Vol 49 (9) ◽  
pp. 030006052110425
Author(s):  
Huai Wu Yuan ◽  
Jin Xun Yao ◽  
Si Yu Huang ◽  
Min Yong Cui ◽  
Ren Jie Ji ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Patient Specific ◽  
Asymmetric Distribution ◽  
Flow Volume ◽  
Risk Area ◽  
Blood Flow Volume ◽  
Wall Shear ◽  
The Right

The effects of increasing blood flow on the pathogenic wall shear stress (pWSS) of subclavian arteries (SAs) are currently unclear. Patient-specific models of the SA were constructed based on computed tomographic images from two patients. Using the Ansys Fluent 19.0 transient laminar flow solver, the finite volume method was chosen to solve the Navier–Stokes equation governing fluid behavior. The time-averaged wall shear stress, ratio of risk area, cumulative ratio of risk area ([Formula: see text]), ratio of risk time, and ratio contour of risk time were calculated to describe the temporal and spatial distributions of pWSS. Virtually all pWSS occurred during the diastolic phase. The [Formula: see text]was 2.3 and 1.29 times higher on the left than on the right in Patients 1 (P1) and 2 (P2), respectively. Increasing the blood flow volume of the left SA by 20%, 40%, and 60% led to a 9.27%, 15.10%, and 20.99% decrease in[Formula: see text] for P1 and a 5.74%, 11.55%, and 17.14% decrease in [Formula: see text] for P2, respectively, compared with baseline values. In conclusion, the left SA showed greater diastolic pWSS than the right SA, and increasing the blood flow volume reduced the pWSS in the left SA.

scholarly journals Influence of the femoral artery-graft junction patient-specific geometry on blood flow structure and wall shear stress

2021 ◽  
Vol 2103 (1) ◽  
pp. 012209
Author(s):  
Y F Ivanova ◽  
L G Tikhomolova ◽  
A D Yukhnev ◽  
E M Smirnov ◽  
R V Kalmikova ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Femoral Artery ◽  
Numerical Study ◽  
Common Femoral Artery ◽  
Patient Specific ◽  
Geometrical Parameters ◽  
Artery Graft ◽  
Wall Shear

Abstract The paper presents a comparative numerical study of pulsatory blood flow in five patient-specific models of femoral-popliteal artery anastomosis. Three-dimensional geometric models of a proximal junction of the common femoral artery/graft were constructed on the bases of CT angiography. The influence of junction geometry on the blood flow and wall shear stress is analyzed. The ratio of the measured CFA and graft diameters and the junction angle are considered as the major geometrical parameters. Numerically calculated velocity fields are analyzed, and stagnant zones in the anastomoses flow are identified. Time-averaged distributions of wall shear stress and oscillatory shear index obtained for five patient-specific model are compared.

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