scholarly journals Dynamics of pulsatile flow through model abdominal aortic aneurysms

2014 ◽  
Vol 758 ◽  
pp. 150-179 ◽  
Author(s):  
Shyam Sunder Gopalakrishnan ◽  
Benoît Pier ◽  
Arie Biesheuvel
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Maximal Diameter ◽  
Abdominal Aortic ◽  
Flow Phenomena ◽  
Pulsatile Flows ◽  
Wall Shear

AbstractTo contribute to the understanding of flow phenomena in abdominal aortic aneurysms, numerical computations of pulsatile flows through aneurysm models and a stability analysis of these flows were carried out. The volume flow rate waveforms into the aneurysms were based on measurements of these waveforms, under rest and exercise conditions, of patients suffering abdominal aortic aneurysms. The Reynolds number and Womersley number, the dimensionless quantities that characterize the flow, were varied within the physiologically relevant range, and the two geometric quantities that characterize the model aneurysm were varied to assess the influence of the length and maximal diameter of an aneurysm on the details of the flow. The computed flow phenomena and the induced wall shear stress distributions agree well with what was found in PIV measurements by Salsac et al. (J. Fluid Mech., vol. 560, 2006, pp. 19–51). The results suggest that long aneurysms are less pathological than short ones, and that patients with an abdominal aortic aneurysm are better to avoid physical exercise. The pulsatile flows were found to be unstable to three-dimensional disturbances if the aneurysm was sufficiently localized or had a sufficiently large maximal diameter, even for flow conditions during rest. The abdominal aortic aneurysm can be viewed as acting like a ‘wavemaker’ that induces disturbed flow conditions in healthy segments of the arterial system far downstream of the aneurysm; this may be related to the fact that one-fifth of the larger abdominal aortic aneurysms are found to extend into the common iliac arteries. Finally, we report a remarkable sensitivity of the wall shear stress distribution and the growth rate of three-dimensional disturbances to small details of the aneurysm geometry near the proximal end. These findings suggest that a sensitivity analysis is appropriate when a patient-specific computational study is carried out to obtain a quantitative description of the wall shear stress distribution.

scholarly journals Wall shear stress and endothelial cells dysfunction in the context of abdominal aortic aneurysms

2013 ◽  
Vol 16 (sup1) ◽  
pp. 27-29 ◽  
Author(s):  
Z. Macek Jilkova ◽  
V. Deplano ◽  
C. Verdier ◽  
M. Toungara ◽  
C. Geindreau ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Abdominal Aortic ◽  
Wall Shear

Shear Stress and Angiotensin II in the Development and Localization of Abdominal Aortic Aneurysms

2009 ◽  
Author(s):  
Michelle Consolini ◽  
Tiziano Passerini ◽  
Marina Piccinelli ◽  
Brandon Fornwalt ◽  
Nick G. Willett ◽  
...  
Keyword(s):  
Shear Stress ◽  
Angiotensin Ii ◽  
Wall Shear Stress ◽  
Lower Extremities ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Infrarenal Aorta ◽  
Abdominal Aortic ◽  
Suprarenal Aorta ◽  
Wall Shear

Abdominal aortic aneurysms (AAAs) develop in the infrarenal aorta of humans and in the suprarenal aorta of apoE−/− mice infused with angiotensin II (AngII). Oscillatory wall shear stress in the infrarenal human abdominal aorta is driven by the flow to the gastric arteries, the lumbar curvature and the capacitance of the lower extremities [1]. Two of these factors, the lumbar curvature and the capacitance of the lower extremities, are significantly different in mice than in humans. Therefore, we hypothesized that the differences in localization of AAAs between species is explained by differences in the pattern of wall shear stress via the shear-regulated modulation of inflammatory pathways involving AngII.

scholarly journals Mechanical Platelet Activation Potential in Abdominal Aortic Aneurysms

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Kirk B. Hansen ◽  
Amirhossein Arzani ◽  
Shawn C. Shadden
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Platelet Activation ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Study Patient ◽  
Abdominal Aortic ◽  
Activation Potential ◽  
Wall Shear ◽  
Rest And Exercise

Intraluminal thrombus (ILT) in abdominal aortic aneurysms (AAA) has potential implications to aneurysm growth and rupture risk; yet, the mechanisms underlying its development remain poorly understood. Some researchers have proposed that ILT development may be driven by biomechanical platelet activation within the AAA, followed by adhesion in regions of low wall shear stress. Studies have investigated wall shear stress levels within AAA, but platelet activation potential (AP) has not been quantified. In this study, patient-specific computational fluid dynamic (CFD) models were used to analyze stress-induced AP within AAA under rest and exercise flow conditions. The analysis was conducted using Lagrangian particle-based and Eulerian continuum-based approaches, and the results were compared. Results indicated that biomechanical platelet activation is unlikely to play a significant role for the conditions considered. No consistent trend was observed in comparing rest and exercise conditions, but the functional dependence of AP on stress magnitude and exposure time can have a large impact on absolute levels of anticipated platelet AP. The Lagrangian method obtained higher peak AP values, although this difference was limited to a small percentage of particles that falls below reported levels of physiologic background platelet activation.

Blood Flow in Abdominal Aortic Aneurysms: Pulsatile Flow Hemodynamics

2001 ◽  
Vol 123 (5) ◽  
pp. 474-484 ◽  
Author(s):  
Ender A. Finol ◽  
Cristina H. Amon
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pulsatile Flow ◽  
Peak Flow ◽  
Abdominal Aortic Aneurysms ◽  
Reynolds Numbers ◽  
Aortic Aneurysms ◽  
Abdominal Aortic ◽  
Wall Shear

Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged 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 characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure pw, wall shear stress τw, and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.

Hemodynamics in Human Abdominal Aortic Aneurysms During Rest and Simulated Exercise

2007 ◽  
Author(s):  
Andrea S. Les ◽  
Christopher P. Cheng ◽  
Mary T. Draney Blomme ◽  
C. Alberto Figueroa ◽  
John F. LaDisa ◽  
...  
Keyword(s):  
United States ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Surgical Repair ◽  
Abdominal Aortic Aneurysms ◽  
The United States ◽  
Aortic Aneurysms ◽  
High Particle ◽  
Abdominal Aortic ◽  
Natural Progression

Abdominal Aortic Aneurysms (AAAs) — the localized enlargement of the abdominal aorta — represent the 13th leading cause of death in the United States. The natural progression of small (3–5 cm) AAAs is 2–6% growth per year until rupture or surgical repair [1]. As AAAs enlarge, adverse hemodynamic conditions (including regions of low mean wall shear stress and high particle residence time) are exacerbated under normal resting conditions.

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.

Wall Shear Stress and Intraluminal Thrombus Changes in Abdominal Aortic Aneurysms: Study With Longitudinal Patients

2013 ◽  
Author(s):  
B. Zambrano ◽  
F. Jaberi ◽  
W. Lee ◽  
S. Baek
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Thrombus Formation ◽  
Fluid Dynamic ◽  
Surface Displacement ◽  
Aortic Aneurysms ◽  
Intraluminal Thrombus ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Wall Shear

Abdominal Aortic Aneurysm (AAA), a focal enlargement of the abdominal aorta is an ongoing process that can be affected by many parameters. Among these parameters, hemodynamics and intraluminal thrombus layer (ILT) play important roles on AAA growth. It is widely accepted that hemodynamic forces (normal and shear forces) have a profound impact on the mechano-homeostasis of the arterial wall and its vascular remodeling. The role of ILT, however, remains controversial. Some studies suggest that ILT may be beneficial by shieling the weak aneurysm wall, whereas others claim that the presence of ILT can lead to immune responses that increase protease breakdown of collagen and elastin, adversely affecting wall strength. ILT is formed by the deposition of blood clots called thrombus. Thrombus formation is achieved through different mechanisms, but all research agrees that shear fluid forces are one of the key parameters for the formation and development of ILT. There are few studies to date that use these three parameters to assess the evolution of AAAs growth. Here, we explore the relation between wall shear stress (WSS), ILT and AAA expansion using longitudinal CT images from follow-up studies from 3 patients (a total of 8 scans). We used geometrical models of AAAs segmented from patient images to estimate outer surface displacement, ILT, and tissue thickness. Additionally, we used fluid dynamic data to estimate wall shear stress at peak systolic. These parameters were then used to investigate possible relationships with each other.

Effect of Wall Shear Stress on Abdominal Aortic Aneurysm Expansion: Study With Longitudinal Patient Images

2012 ◽  
Author(s):  
B. Zambrano ◽  
A. Dupay ◽  
F. Jaberi ◽  
W. Lee ◽  
S. Baek
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Open Surgery ◽  
Vascular Diseases ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Abdominal Aortic ◽  
Reduce Risk ◽  
Wall Shear

Abdominal Aortic Aneurysms (AAA), a focal enlargement of abdominal aorta, is a form of vascular diseases that affects large part of the population. It can cause the mortality up to 90% of the cases when it ruptures. Currently, the best known treatment to reduce risk is open surgery or endovascular repair. Since the risk of such surgery repair is high, in most patients with AAAs< 55mm in its maximum diameter the surgical treatment is postponed. An effort to enhance the accuracy of the risk assessment and to prevent AAA’s growth and rupture is being made, but the mechanisms promoting AAAs growth are still largely unknown. AAAs can be affected by different factors, among those, hemodynamics is known to play important roles in AAA initiation and progression. Particularly, the wall shear stress is believed to contribute to AAA expansion and rupture. For the present study, we use geometries constructed from longitudinal CT images obtained during AAA follow-up studies and investigate relations between multiple hemodynamics factors with local expansion of AAAs.

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