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.

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.

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 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.

Influence of Hemodialysis Catheter Insertion on Hemodynamics in the Central Veins

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Min-Hyuk Park ◽  
Yue Qiu ◽  
Haoyao Cao ◽  
Ding Yuan ◽  
Da Li ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Thrombus Formation ◽  
Patient Specific ◽  
Flow Disturbance ◽  
Computed Tomography Images ◽  
Relative Residence Time ◽  
Wall Shear ◽  
The Impact

Abstract Central venous catheter (CVC) related thrombosis is a major cause of CVC dysfunction in patients under hemodialysis. The aim of our study was to investigate the impact of CVC insertion on hemodynamics in the central veins and to examine the changes in hemodynamic environments that may be related to thrombus formation due to the implantation of CVC. Patient-specific models of the central veins with and without CVC were reconstructed based on computed tomography images. Flow patterns in the veins were numerically simulated to obtain hemodynamic parameters such as time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), relative residence time (RRT), and normalized transverse wall shear stress (transWSS) under pulsatile flow. The non-Newtonian effects of blood flow were also analyzed using the Casson model. The insertion of CVC caused significant changes in the hemodynamic environment in the central veins. A greater disturbance and increase of velocity were observed in the central veins after the insertion of CVC. As a result, TAWSS and transWSS were markedly increased, but most parts of OSI and RRT decreased. Newtonian assumption of blood flow would overestimate the increase in TAWSS after CVC insertion. High wall shear stress (WSS) and flow disturbance, especially the multidirectionality of the flow, induced by the CVC may be a key factor in initiating thrombosis after CVC insertion. Accordingly, approaches to decrease the flow disturbance during CVC insertion may help restrain the occurrence of thrombosis. More case studies with pre-operative and postoperative modeling and clinical follow-up need to be performed to verify these findings. Non-Newtonian blood flow assumption is recommended in computational fluid dynamics (CFD) simulations of veins with CVCs.

scholarly journals Characterizations and Correlations of Wall Shear Stress in Aneurysmal Flow

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Amirhossein Arzani ◽  
Shawn C. Shadden
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Patient Specific ◽  
Spatial Gradient ◽  
Abdominal Aortic ◽  
Wall Shear ◽  
Highly Correlated ◽  
Definition Of ◽  
Traditional Approaches

Wall shear stress (WSS) is one of the most studied hemodynamic parameters, used in correlating blood flow to various diseases. The pulsatile nature of blood flow, along with the complex geometries of diseased arteries, produces complicated temporal and spatial WSS patterns. Moreover, WSS is a vector, which further complicates its quantification and interpretation. The goal of this study is to investigate WSS magnitude, angle, and vector changes in space and time in complex blood flow. Abdominal aortic aneurysm (AAA) was chosen as a setting to explore WSS quantification. Patient-specific computational fluid dynamics (CFD) simulations were performed in six AAAs. New WSS parameters are introduced, and the pointwise correlation among these, and more traditional WSS parameters, was explored. WSS magnitude had positive correlation with spatial/temporal gradients of WSS magnitude. This motivated the definition of relative WSS gradients. WSS vectorial gradients were highly correlated with magnitude gradients. A mix WSS spatial gradient and a mix WSS temporal gradient are proposed to equally account for variations in the WSS angle and magnitude in single measures. The important role that WSS plays in regulating near wall transport, and the high correlation among some of the WSS parameters motivates further attention in revisiting the traditional approaches used in WSS characterizations.

scholarly journals The Effect of Beta-Blockers on Hemodynamic Parameters in Patient-Specific Blood Flow Simulations of Type-B Aortic Dissection: An Virtual Study

2021 ◽  
Author(s):  
Mohammad Amin Abazari ◽  
Deniz Rafieianzab ◽  
M. Soltani ◽  
Mona Alimohammadi
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Dissection ◽  
Antihypertensive Drugs ◽  
Patient Specific ◽  
Hemodynamic Parameters ◽  
Type B ◽  
Type B Aortic Dissection ◽  
Wall Shear

Abstract Type-B aortic dissection (AD) is one of the greatest complex and fatal conditions with co-occurring disorders, challenging to treat. The initial treatment for patients presenting with AD is medical intervention to stabilize the condition. In the present study, a patient-specific geometry of type-B AD is generated from computed tomography images, and a three-element Windkessel lumped parameter model is implemented at the outlets to realistic boundary conditions. According to the physiological response of the antihypertensive drugs in the reduction of aortic blood flow and heart rate, three case studies with different heart rates have been created. Hemodynamic distributions including wall shear stress indicators, velocity and pressure are investigated and compared in each model. Results show that there is a considerable reduction in pressure furthermore, time-averaged wall shear stress (TAWSS) values decreased by 25% and 30%, respectively. Main goal is to critically analysis the use of biomechanical and computational simulation tools to measure hemodynamic parameters in the absence and presence of antihypertensive drugs. It would be of significant use to clinicians to improve diagnostic and treatment planning.

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