Influence of Non-Newtonian Models on Simulation of Aneurysm Hemodynamics

2008 ◽  
Author(s):  
Jenn Rossmann ◽  
Carolyn Fisher
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Wall Shear Stress ◽  
Flow Patterns ◽  
Aneurysm Rupture ◽  
Patient Specific ◽  
Hemodynamic Forces ◽  
Aneurysm Formation ◽  
Geometric Factors ◽  
Aneurysm Development

Aneurysm rupture rates are often associated with factors such as size, location, and patient specific risks such as age and health. However, the actual physiological causes of the pathogenesis, enlargement, and rupture are unclear. Many studies have shown aneurysm formation to be mechanically mediated. Hemodynamic forces such as wall shear stress (WSS), pressure, and flow patterns have been examined as causes for aneurysm development and eventual rupture [1]. Geometric factors such as the aneurysm size, shape, and aspect ratio may also be important in predicting rupture [2,3].

scholarly journals Wall shear stress gradient is independently associated with middle cerebral artery aneurysm development: a case-control CFD patient-specific study based on 77 patients

BMC Neurology ◽  
2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Mikołaj Zimny ◽  
Edyta Kawlewska ◽  
Anna Hebda ◽  
Wojciech Wolański ◽  
Piotr Ładziński ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Middle Cerebral Artery ◽  
Cerebral Artery ◽  
Case Control ◽  
Independent Effect ◽  
Patient Specific ◽  
Aneurysm Formation ◽  
Wall Shear ◽  
Mca Aneurysm

Abstract Background Previously published computational fluid dynamics (CFD) studies regarding intracranial aneurysm (IA) formation present conflicting results. Our study analysed the involvement of the combination of high wall shear stress (WSS) and a positive WSS gradient (WSSG) in IA formation. Methods We designed a case-control study with a selection of 38 patients with an unruptured middle cerebral artery (MCA) aneurysm and 39 non-aneurysmal controls to determine the involvement of WSS, oscillatory shear index (OSI), the WSSG and its absolute value (absWSSG) in aneurysm formation based on patient-specific CFD simulations using velocity profiles obtained from transcranial colour-coded sonography. Results Among the analysed parameters, only the WSSG had significantly higher values compared to the controls (11.05 vs − 14.76 [Pa/mm], P = 0.020). The WSS, absWSSG and OSI values were not significantly different between the analysed groups. Logistic regression analysis identified WSS and WSSG as significant co-predictors for MCA aneurysm formation, but only the WSSG turned out to be a significant independent prognosticator (OR: 1.009; 95% CI: 1.001–1.017; P = 0.025). Significantly more patients (23/38) in the case group had haemodynamic regions of high WSS combined with a positive WSSG near the bifurcation apex, while in the control group, high WSS was usually accompanied by a negative WSSG (14/39). From the analysis of the ROC curve for WSSG, the area under the curve (AUC) was 0.654, with the optimal cut-off value −0.37 Pa/mm. The largest AUC was recognised for combined WSS and WSSG (AUC = 0.671). Our data confirmed that aneurysms tend to form near the bifurcation apices in regions of high WSS values accompanied by positive WSSG. Conclusions The development of IAs is determined by an independent effect of haemodynamic factors. High WSS impacts MCA aneurysm formation, while a positive WSSG mainly promotes this process.

Clinical, morphological, and hemodynamic independent characteristic factors for rupture of posterior communicating artery aneurysms

2015 ◽  
Vol 8 (8) ◽  
pp. 808-812 ◽  
Author(s):  
Ying Zhang ◽  
Linkai Jing ◽  
Jian Liu ◽  
Chuanhui Li ◽  
Jixing Fan ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Univariate Analysis ◽  
Multivariate Logistic Regression Analysis ◽  
Aneurysm Rupture ◽  
Irregular Shape ◽  
Posterior Communicating Artery ◽  
Patient Specific ◽  
Younger Age ◽  
Wall Shear

ObjectiveTo identify clinical, morphological, and hemodynamic independent characteristic factors that discriminate posterior communicating artery (PCoA) aneurysm rupture status.Methods173 patients with single PCoA aneurysms (108 ruptured, 65 unruptured) between January 2012 and June 2014 were retrospectively collected. Patient-specific models based on their three-dimensional digital subtraction angiography images were constructed and analyzed by a computational fluid dynamic method. All variables were analyzed by univariate analysis and multivariate logistic regression analysis.ResultsTwo clinical factors (younger age and atherosclerosis), three morphological factors (higher aspect ratio, bifurcation type, and irregular shape), and six hemodynamic factors (lower mean and minimum wall shear stress, higher oscillatory shear index, a greater portion of area under low wall shear stress, unstable and complex flow pattern) were significantly associated with PCoA aneurysm rupture. Independent factors characterizing the rupture status were identified as age (OR 0.956, p=0.015), irregular shape (OR 6.709, p<0.001), and minimum wall shear stress (OR 0.001, p=0.038).ConclusionsWe combined clinical, morphological, and hemodynamic characteristics analysis and found the three strongest independent factors for PCoA aneurysm rupture were younger age, irregular shape, and low minimum wall shear stress. This may be useful for guiding risk assessments and subsequent treatment decisions for PCoA aneurysms.

scholarly journals Propose a Wall Shear Stress Divergence to Estimate the Risks of Intracranial Aneurysm Rupture

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Y. Zhang ◽  
H. Takao ◽  
Y. Murayama ◽  
Y. Qian
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Intracranial Aneurysm ◽  
Risk Estimation ◽  
Aneurysm Rupture ◽  
Patient Specific ◽  
Luminal Surface ◽  
Risk Of Rupture ◽  
Computational Fluid Dynamics Cfd ◽  
Wall Shear

Although wall shear stress (WSS) has long been considered a critical indicator of intracranial aneurysm rupture, there is still no definite conclusion as to whether a high or a low WSS results in aneurysm rupture. The reason may be that the effect of WSS direction has not been fully considered. The objectives of this study are to investigate the magnitude of WSS (WSS) and its divergence on the aneurysm surface and to test the significance of both in relation to the aneurysm rupture. Patient-specific computational fluid dynamics (CFD) was used to compute WSS and wall shear stress divergence (WSSD) on the aneurysm surface for nineteen patients. Our results revealed that if highWSSis stretching aneurysm luminal surface, and the stretching region is concentrated, the aneurysm is under a high risk of rupture. It seems that, by considering both direction and magnitude of WSS, WSSD may be a better indicator for the risk estimation of aneurysm rupture (154).

scholarly journals Effects of Disturbed Flow on Vascular Endothelium: Pathophysiological Basis and Clinical Perspectives

2011 ◽  
Vol 91 (1) ◽  
pp. 327-387 ◽  
Author(s):  
Jeng-Jiann Chiu ◽  
Shu Chien
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Patterns ◽  
Arterial Tree ◽  
Disturbed Flow ◽  
Hemodynamic Forces ◽  
Venous Diseases ◽  
Wall Shear

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

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

2018 ◽  
Vol 128 (3) ◽  
pp. 723-730 ◽  
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.

Patient-Specific Modelling of Aortic Arch Wall Shear Stress Patterns in Patients With Marfan Syndrome

2009 ◽  
Author(s):  
Bram Trachet ◽  
Daniel Devos ◽  
Julie De Backer ◽  
Anne De Paepe ◽  
Bart L. Loeys ◽  
...  
Keyword(s):  
Shear Stress ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Marfan Syndrome ◽  
Aortic Root ◽  
Arterial System ◽  
Patient Specific ◽  
Physiological Data ◽  
Aneurysm Formation ◽  
Wall Shear

Marfan syndrome (MFS) is a genetic connective tissue disorder with a high prevalence of aortic aneurysm formation (a pathological dilatation of the aorta), typically at the aortic root. The disorder is caused by mutations in the gene encoding fibrillin-1 [1]. Recently, it has been shown in mouse models that selected manifestations of MFS, such as aortic aneurysm formation, can be explained by excessive signaling by the transforming growth factor–beta (TGF-beta) family of cytokines [2]. Although the footprint of the disease is clearly genetic, there is still a role for (computational) biomechanics and hemodynamics to elucidate why aneurysms develop preferentially at the level of the aortic root, since the genetic defect affects the entire (arterial) system. One of the most obvious parameters to study is the arterial wall shear stress (WSS). WSS plays an important role in the regulation of the vascular system and is considered a significant factor in the development and progression of cardiovascular disease in humans. Low and/or oscillating values of WSS have been associated with the formation of atherosclerotic lesions [3] and with the growth of aneurysms [4]. It is, however, hard to show a link between low WSS and aneurysm initiation, since in most cases the geometrical and physiological data are lacking during the first and most important stages of the aneurysm development. Furthermore follow-up studies in human patients are difficult, since aneurysms grow very slowly (only 0.9 mm/year in MFS patients treated with beta-blockers) and it will take several years before significant changes will have taken place. Therefore, in this study, we have computed the aortic flow field and WSS patterns for 5 different MFS patients with ages varying from 14 to 54 years old, in order to get an idea about the effect of age on the development of the disease.

Comparison of Carotid Bifurcation Hemodynamics in Patient-Specific Geometries at Rest and During Exercise

2013 ◽  
Author(s):  
Rodward L. Hewlin ◽  
John P. Kizito
Keyword(s):  
Cardiovascular Disease ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Normal Stress ◽  
Carotid Bifurcation ◽  
Flow Patterns ◽  
Patient Specific ◽  
Local Risk ◽  
Wall Shear ◽  
Hemodynamic Flow

The ultimate goal of the present study is to determine whether investigations of flow patterns (flow reversal and flow branching) and mechanical factors (wall shear stress and normal stress) have a role in local risk factors and if flow modeling can truly rely on surrogate geometric sites (simplified geometries). Cardiovascular disease is considered to be the leading cause of morbidity and mortality across the world and improved methods of disease management are desperately needed. One of the main forms of cardiovascular disease is atherosclerosis. The presence of atherosclerotic plaques has been shown to be closely related to arterial vessel geometry and hemodynamic flow patterns. Computational fluid dynamic simulations were performed on 3 carotid bifurcation arteries to demonstrate that hemodynamic factors are significant determinants for the development of vascular pathology. Relationships between disturbed flow and various geometric factors from rest-state and exercise were examined. Wall shear stress, normal stress, and vorticity were used to verify the role of age, gender, and geometry on hemodynamic flow patterns.

Two Diverse Hemodynamic Forces, a Mechanical Stretch and a High Wall Shear Stress, Determine Intracranial Aneurysm Formation

2019 ◽  
Vol 11 (1) ◽  
pp. 80-92 ◽  
Author(s):  
Hirokazu Koseki ◽  
Haruka Miyata ◽  
Satoshi Shimo ◽  
Nobuhiko Ohno ◽  
Kazuma Mifune ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Intracranial Aneurysm ◽  
Mechanical Stretch ◽  
High Wall Shear Stress ◽  
Hemodynamic Forces ◽  
Aneurysm Formation ◽  
Wall Shear

Y-Stent Coiling of Basilar Bifurcation Aneurysms Induces a Dynamic Angular Vascular Remodeling With Alteration of the Apical Wall Shear Stress Pattern

Neurosurgery ◽  
2012 ◽  
Vol 72 (4) ◽  
pp. 617-629 ◽  
Author(s):  
Bulang Gao ◽  
Merih I. Baharoglu ◽  
Alex D. Cohen ◽  
Adel M. Malek
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Dynamic Analysis ◽  
Computational Fluid Dynamic ◽  
Fluid Dynamic ◽  
Cerebral Arteries ◽  
Patient Specific ◽  
Computational Fluid Dynamic Analysis ◽  
Hemodynamic Forces ◽  
Wall Shear

Abstract BACKGROUND: Although wide-necked basilar bifurcation aneurysms are treated with Y-stent coiling, the effect of this intervention on vessel configuration and hemodynamics is unknown. OBJECTIVE: To investigate the immediate and delayed effects of Y-stenting using self-expanding microstents on basilar bifurcation architecture and hemodynamics. METHODS: Fifteen patients underwent basilar Y-stent coiling and imaging with rotational angiography. Vascular angles were measured between proximal P1 segments of the posterior cerebral arteries (α) and between the basilar artery and each P1 segment (β1,2) in the anteroposterior and γ1,2 sagittal planes. Patient-specific computational fluid dynamic analysis was used to estimate wall shear stress (WSS) changes with treatment. RESULTS: In the anteroposterior plane, Y-stenting significantly decreased angle α and increased β angles immediately after stent coiling (P &lt; .05 and P &lt; .01, respectively) in a continued dynamic remodeling that progressed further in later months; sagittal γ angles also decreased (P &lt; .0001). This novel stent-induced geometric progressive remodeling resulted in effective straightening and narrowing of the basilar bifurcation angle α (150.0 degrees vs 113 degrees, P &lt; .0001) with significant correlation (r = 0.39, P &lt; .05) between pretreatment proximal P1 angles and maximal angular change. Computational fluid dynamic analysis showed the angular remodeling led to significant narrowing of the WSS interpeak at the apex, redirecting high WSS away from the neck transition zone with native vessel toward the inert coil mass. CONCLUSION: Y-configuration stent coiling induced immediate and, more significantly, a previously undefined delayed cerebrovascular remodeling. This progressive stent-induced angular remodeling alters perianeurysmal hemodynamics, independent of the flow-diverting properties of stent struts, thus shifting the balance of hemodynamic forces affecting aneurysm development and evolution.

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

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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