scholarly journals Wall shear stress at the initiation site of cerebral aneurysms

2016 ◽  
Vol 16 (1) ◽  
pp. 97-115 ◽  
Author(s):  
A. J. Geers ◽  
H. G. Morales ◽  
I. Larrabide ◽  
C. Butakoff ◽  
P. Bijlenga ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysms ◽  
Initiation Site ◽  
Wall Shear

Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Matthew D. Ford ◽  
Ugo Piomelli
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
High Frequency ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Disturbed Flow ◽  
Frequency Fluctuations ◽  
Wall Shear ◽  
Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

Analysis of Flow and Wall Shear Stress in Curvature Induced Dorsal Aneurysms: Effect of Arterial Curvature

2009 ◽  
Author(s):  
Arun Ramu ◽  
Guo-Xiang Wang
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Dynamic ◽  
Cerebral Arteries ◽  
Cerebral Aneurysms ◽  
Morbidity Rate ◽  
Mortality And Morbidity ◽  
Wall Shear ◽  
Primary Velocity ◽  
The Impact

Intracranial aneurysms are abnormal enlargement in the walls of cerebral arteries. The rupture of aneurysms is the leading cause of subarachnoid hemorrhage (SAH), with a high mortality and morbidity rate. A majority of saccular cerebral aneurysms occur at sites of arterial bifurcations. However, a good percentage of aneurysms are curvature induced and are found along the cavernous arterial segment. The occurrence of such non branching aneurysms, clinically called dorsal aneurysms, can be related to the increased wall shear stress at the curved arteries. The rupture of aneurysms usually occurs at the dome region, which is subjected to reduced wall shear stress (wss) owing to low re-circulating flow. Hence it is important to understand the impact of arterial curvature on the WSS distribution along the dome of aneurysms. Previously, studies have not taken into account the aspect of low WSS along the dome region. In the present 3-d computational fluid dynamic approach, we investigate the impact of varying arterial curvature on spherical dorsal aneurysms. The primary velocity patterns, the WSS distribution along the dome of the aneurysm and the area of increased WSS have been quantified for steady flow conditions.

Differential Gene Expression of Endothelial Cells Under High Wall Shear Stress and Spatial Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Song Liu ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Flow Acceleration ◽  
Spatial Gradients ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature. Due to the focal nature of aneurysm development it has long been speculated that hemodynamics are an important factor in aneurysm susceptibility. The local hemodynamics of bifurcations are complex, being characterized by flow impingement causing a high frictional force on the vessel wall known as wall shear stress (WSS) and significant flow acceleration or deceleration, manifested as the positive or negative spatial gradient of WSS (WSSG). In vivo studies have recently identified that aneurysm initiation occurs at areas of the vessel wall that experience a combination of both high WSS and positive WSSG [1,2]

Positive and Negative Wall Shear Stress Gradients Have Different Effects on Endothelial Phenotype Under High Wall Shear Stress

2011 ◽  
Author(s):  
Jennifer Dolan ◽  
Frasier Sim ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Cerebral Vasculature ◽  
High Wall Shear Stress ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature where the blood vessel wall experiences complex hemodynamics. In vivo studies have recently revealed that the initiation of cerebral aneurysms is confined to a well-defined hemodynamic microenvironment [1,2]. Metaxa et al. [2] found that early aneurysm remodeling initiates where the vessel wall experiences high wall shear stress (WSS) and flow is accelerating, thus creating a positive spatial gradient in WSS (WSSG). Closer examination of such in vivo studies reveals that exposure of the vessel wall to equally high WSS in the presence of decelerating flow, that is, negative WSSG, does not result in aneurysm-like destruction.

Differential Responses of Endothelial Cells to Positive and Negative Wall Shear Stress Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Sukhjinder Singh ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Fluid Shear Stress ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Outer Side ◽  
Fluid Shear ◽  
Wall Shear

Cerebral aneurysms tend to develop at bifurcation apices or the outer side of curved vessels where the blood vessel wall experiences complex hemodynamics. In vivo studies have recently revealed that the initiation of cerebral aneurysms is confined to a well-defined hemodynamic microenvironment. Specifically aneurysms form where the vessel wall experiences high fluid shear stress (wall shear stress, WSS) and flow is accelerating, so that the wall is exposed to a positive spatial gradient in the fluid shear stress (wall shear stress gradient, WSSG)[1,2]. Closer examination of such in vivo studies reveals that exposure of the vessel wall to equally high WSS in the presence of decelerating flow, that is, negative WSSG, does not result in aneurysm-like remodeling.

Aneurysms of the Posterior Communicating Artery: Hemodynamics and Shapes

2009 ◽  
Author(s):  
Svetlana Khvostova ◽  
Christopher Putman ◽  
Juan R. Cebral
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysms ◽  
Clinical History ◽  
Posterior Communicating Artery ◽  
Geometrical Shape ◽  
Arterial Hemodynamics ◽  
Biological Responses ◽  
Single Location ◽  
Wall Shear

The pathogenesis, progression and rupture of cerebral aneurysms are multi-factorial mechanisms that involve arterial hemodynamics, wall biomechanics, wall mechano-transduction or mechano-biology, and peri-aneurysmal environmental effects [1]. However, the interaction and relative importance of these factors remains poorly understood. Presumably, the geometrical shape and evolution of aneurysms are governed by the interaction between hemodynamic stimuli (wall shear stress) and the biological responses of the arterial wall. In order to better understand this interaction, the goal of this study was to characterize and relate the geometrical shapes of intracranial aneurysms at a single location, the posterior communicating artery (PComA), to blood flow patterns, wall shear stress (WSS), and clinical history of previous rupture.

Colocalization of thin-walled dome regions with low hemodynamic wall shear stress in unruptured cerebral aneurysms

2013 ◽  
Vol 119 (1) ◽  
pp. 172-179 ◽  
Author(s):  
Laith M. Kadasi ◽  
Walter C. Dent ◽  
Adel M. Malek
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Wall Shear Stress ◽  
Cerebral Aneurysms ◽  
Pressure Differential ◽  
Time Dependent ◽  
Aneurysm Wall ◽  
Thin Walled ◽  
Wall Shear ◽  
Unruptured Cerebral Aneurysms

Object Wall shear stress (WSS) plays a role in regulating endothelial function and has been suspected in cerebral aneurysm rupture. The aim of this study was to evaluate the spatial relationship between localized thinning of the aneurysm dome and estimated hemodynamic factors, hypothesizing that a low WSS would correlate with aneurysm wall degeneration. Methods Steady-state computational fluid dynamics analysis was performed on 16 aneurysms in 14 patients based on rotational angiographic volumes to derive maps of WSS, its spatial gradient (WSSG), and pressure. Local dome thickness was estimated categorically based on tissue translucency from high-resolution intraoperative microscopy findings. Each computational model was oriented to match the corresponding intraoperative view and numerically sampled in thin and normal adjacent dome regions, with controls at the neck and parent vessel. The pressure differential was computed as the difference between aneurysm dome points and the mean neck pressure. Pulsatile time-dependent confirmatory analysis was carried out in 7 patients. Results Matched-pair analysis revealed significantly lower levels of WSS (0.381 Pa vs 0.816 Pa; p < 0.0001) in thin-walled dome areas than in adjacent baseline thickness regions. Similarly, log WSSG and log WSS × WSSG were both lower in thin regions (both p < 0.0001); multivariate logistic regression analysis identified lower WSS and higher pressure differential as independent correlates of lower wall thickness with an area under the curve of 0.80. This relationship was observed in both steady-state and time-dependent pulsatile analyses. Conclusions Thin-walled regions of unruptured cerebral aneurysms colocalize with low WSS, suggesting a cellular mechanotransduction link between areas of flow stasis and aneurysm wall thinning.

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

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.

Sign in / Sign up

Export Citation Format

Share Document