An Effect of Aspect Ratio and Roughness on the Wall Shear Stress of Open Channel

A parabolic numerical analysis procedure has been used to predict the flow in a straight, radial rotating channel of rectangular cross-section, chosen as a simple model of an impeller passage. A two equation turbulence model was employed, with alternative modifications, to include the influence of Coriolis force on turbulent kinetic energy. Alternative Coriolis force terms were evaluated by comparisons in a high-aspect-ratio duct with measured velocity, wall shear stress and turbulent viscosity. Secondary velocity predictions were checked with data from a low-aspect-ratio duct where the Coriolis modification of turbulence was found less influential than the secondary flow in the modification of side wall shear stress.

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CFD Study of the Relationship Between Wall Shear Stress and Aspect Ratio in Elastase Induced Rabbit Aneurysm Models

ASME 2008 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2008-193139 ◽

2008 ◽

Cited By ~ 1

Author(s):

Zijing Zeng ◽

Hasballah Zakaria ◽

Ramanathan Kadirvel ◽

Yong-Hong Ding ◽

Debra A. Lewis ◽

...

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Maximum Diameter ◽

Altered Expression ◽

Aneurysm Neck ◽

Aspect Ratios ◽

Risk Of Rupture ◽

Wall Shear

Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. In-vitro studies have demonstrated a correlation between the magnitude and distribution of wall shear stress (WSS) and biological response of both endothelial cells and smooth muscle cells [1–3]. In elastase induced saccular aneurysms, low WSS (below 0.5 Pa) was found to have a correlation with altered expression of biological markers [4]. Localized regions of rapid aneurysm growth in-vivo have been shown to be associated with regions where WSS is below a critical value of 0.1 Pa [5]. Further, aspect ratio (AR), the ratio of the maximum diameter of the aneurysm to the width of the aneurysm neck, has been correlated with elevated risk of rupture [6]. The purpose of the current study is to explore the possibility of creating elastase induced aneurysms in rabbits with a range of aspect ratios (ratio of aneurysm height/neck) and evaluate the existence of a correlation between aspect ratio and WSS distribution. Aneurysms with ARs from 0.98 to 2.8 were created at the origin of the right common carotid artery (n = 30). Qualitative differences in WSS distribution were found in the high AR aneurysms (HARA) (AR>1.6) and low AR aneurysms (LARA) (AR<1.6) [7].

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STUDY ON THE RELATIONSHIP BETWEEN WALL SHEAR STRESS AND ASPECT RATIO OF CEREBRAL ANEURYSMS WITH DIFFERENT PRESSURE DIFFERENCES USING CFD SIMULATIONS

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519418500550 ◽

2018 ◽

Vol 18 (05) ◽

pp. 1850055

Author(s):

ALFREDO ARANDA ◽

ALVARO VALENCIA

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Cfd Simulations ◽

Unruptured Aneurysms ◽

Ruptured Aneurysms ◽

Sphericity Index ◽

Wall Shear ◽

The Relationship

CFD simulations were performed for 60 human cerebral aneurysms (30 previously ruptured and 30 previously unruptured) to study the behavior of the time-averaged wall shear stress (TAWSS) with respect to the aspect ratio (AR), implementing a set of low, normal, and high-pressure differences between the inlet and the outlets of each artery. It is well known that there exists a direct relationship between TAWSS and the rupture. In this investigation, we presented an important result because the condition of the pressure among the branches and the AR may be measured in any patient, then a slope may be associated, and finally a TAWSS may be estimated. We found that when the pressure difference increased, the absolute slopes between TAWSS and AR increased as well. Also, the magnitude of the slope in the previously unruptured aneurysms was 4.7 times the slope in the previously ruptured aneurysms. On the other hand, TAWSS was higher in the previously unruptured aneurysm than previously ruptured aneurysms due to the unruptured aneurysms that have a smaller surface area. Furthermore, we analyzed the relationship between TAWSS and other geometric parameters of the aneurysm, such as bottleneck and non-sphericity index; however, no correlation was found for either cases.

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Impact of bifurcation angle and inflow coefficient on the rupture risk of bifurcation type basilar artery tip aneurysms

Journal of Neurosurgery ◽

10.3171/2016.10.jns161695 ◽

2018 ◽

Vol 128 (3) ◽

pp. 723-730 ◽

Cited By ~ 10

Author(s):

Sherif Rashad ◽

Shin-ichiro Sugiyama ◽

Kuniyasu Niizuma ◽

Kenichi Sato ◽

Hidenori Endo ◽

...

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Univariate Analysis ◽

Aneurysm Rupture ◽

Parent Artery ◽

Maximum Height ◽

Rupture Risk ◽

Bifurcation Angle ◽

Wall Shear

OBJECTIVERisk factors for aneurysm rupture have been extensively studied, with several factors showing significant correlations with rupture status. Several studies have shown that aneurysm shape and hemodynamics change after rupture. In the present study the authors investigated a static factor, the bifurcation angle, which does not change after rupture, to understand its effect on aneurysm rupture risk and hemodynamics.METHODSA hospital database was retrospectively reviewed to identify patients with cerebral aneurysms treated surgically or endovascularly in the period between 2008 and 2015. After acquiring 3D rotational angiographic data, 3D stereolithography models were created and computational fluid dynamic analysis was performed using commercially available software. Patient data (age and sex), morphometric factors (aneurysm volume and maximum height, aspect ratio, bifurcation angle, bottleneck ratio, and neck/parent artery ratio), and hemodynamic factors (inflow coefficient and wall shear stress) were statistically compared between ruptured and unruptured groups.RESULTSSeventy-one basilar tip aneurysms were included in this study, 22 ruptured and 49 unruptured. Univariate analysis showed aspect ratio, bifurcation angle, bottleneck ratio, and inflow coefficient were significantly correlated with a ruptured status. Logistic regression analysis showed that aspect ratio and bifurcation angle were significant predictors of a ruptured status. Bifurcation angle was inversely correlated with inflow coefficient (p < 0.0005), which in turn correlated directly with mean (p = 0.028) and maximum (p = 0.014) wall shear stress (WSS) using Pearson's correlation coefficient, whereas aspect ratio was inversely correlated with mean (0.012) and minimum (p = 0.018) WSS.CONCLUSIONSBifurcation angle and aspect ratio are independent predictors for aneurysm rupture. Bifurcation angle, which does not change after rupture, is correlated with hemodynamic factors including inflow coefficient and WSS, as well as rupture status. Aneurysms with the hands-up bifurcation configuration are more prone to rupture than aneurysms with other bifurcation configurations.

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Effects of Low and High Aneurysmal Wall Shear Stress on Endothelial Cell Behavior: Differences and Similarities

Frontiers in Physiology ◽

10.3389/fphys.2021.727338 ◽

2021 ◽

Vol 12 ◽

Author(s):

Sandrine Morel ◽

Sabine Schilling ◽

Mannekomba R. Diagbouga ◽

Matteo Delucchi ◽

Marie-Luce Bochaton-Piallat ◽

...

Keyword(s):

Gene Expression ◽

Extracellular Matrix ◽

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Extracellular Matrix Proteins ◽

Matrix Proteins ◽

Cytoplasmic Actin ◽

Wall Shear ◽

Protein Classes

Background: Intracranial aneurysms (IAs) result from abnormal enlargement of the arterial lumen. IAs are mostly quiescent and asymptomatic, but their rupture leads to severe brain damage or death. As the evolution of IAs is hard to predict and intricates medical decision, it is essential to improve our understanding of their pathophysiology. Wall shear stress (WSS) is proposed to influence IA growth and rupture. In this study, we investigated the effects of low and supra-high aneurysmal WSS on endothelial cells (ECs).Methods: Porcine arterial ECs were exposed for 48 h to defined levels of shear stress (2, 30, or 80 dyne/cm2) using an Ibidi flow apparatus. Immunostaining for CD31 or γ-cytoplasmic actin was performed to outline cell borders or to determine cell architecture. Geometry measurements (cell orientation, area, circularity and aspect ratio) were performed on confocal microscopy images. mRNA was extracted for RNAseq analysis.Results: ECs exposed to low or supra-high aneurysmal WSS were more circular and had a lower aspect ratio than cells exposed to physiological flow. Furthermore, they lost the alignment in the direction of flow observed under physiological conditions. The effects of low WSS on differential gene expression were stronger than those of supra-high WSS. Gene set enrichment analysis highlighted that extracellular matrix proteins, cytoskeletal proteins and more particularly the actin protein family were among the protein classes the most affected by shear stress. Interestingly, most genes showed an opposite regulation under both types of aneurysmal WSS. Immunostainings for γ-cytoplasmic actin suggested a different organization of this cytoskeletal protein between ECs exposed to physiological and both types of aneurysmal WSS.Conclusion: Under both aneurysmal low and supra-high WSS the typical arterial EC morphology molds to a more spherical shape. Whereas low WSS down-regulates the expression of cytoskeletal-related proteins and up-regulates extracellular matrix proteins, supra-high WSS induces opposite changes in gene expression of these protein classes. The differential regulation in EC gene expression observed under various WSS translate into a different organization of the ECs’ architecture. This adaptation of ECs to different aneurysmal WSS conditions may affect vascular remodeling in IAs.

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Analysis of Morphological-Hemodynamic Risk Factors for Aneurysm Rupture Including a Newly Introduced Total Volume Ratio

Journal of Personalized Medicine ◽

10.3390/jpm11080744 ◽

2021 ◽

Vol 11 (8) ◽

pp. 744

Author(s):

Ui Yun Lee ◽

Hyo Sung Kwak

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Volume Ratio ◽

Wall Stress ◽

Aneurysm Rupture ◽

Oscillatory Shear Index ◽

Unstable Flow ◽

Ruptured Aneurysms ◽

Wall Shear

The purpose of this study was to evaluate morphological and hemodynamic factors, including the newly developed total volume ratio (TVR), in evaluating rupture risk of cerebral aneurysms using ≥7 mm sized aneurysms. Twenty-three aneurysms (11 unruptured and 12 ruptured) ≥ 7 mm were analyzed from 3-dimensional rotational cerebral angiography and computational fluid dynamics (CFD). Ten morphological and eleven hemodynamic factors of the aneurysms were qualitatively and quantitatively compared. Correlation analysis between morphological and hemodynamic factors was performed, and the relationship among the hemodynamic factors was analyzed. Morphological factors (ostium diameter, ostium area, aspect ratio, and bottleneck ratio) and hemodynamic factors (TVR, minimal wall shear stress of aneurysms, time-averaged wall shear stress of aneurysms, oscillatory shear index, relative residence time, low wall shear stress area, and ratio of low wall stress area) were statistically different between ruptured and unruptured aneurysms (p < 0.05). By simple regression analysis, the morphological factor aspect ratio and the hemodynamic factor TVR were significantly correlated (r2 = 0.602, p = 0.001). Ruptured aneurysms had complex and unstable flow. In ≥7 mm ruptured aneurysms, high aspect ratio, bottleneck ratio, complex flow, unstable flow, low TVR, wall shear stress at aneurysm, high oscillatory shear index, relative resistance time, low wall shear stress area, and ratio of low wall stress area were significant in determining the risk of aneurysm rupture.

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