Simple method for evaluating the mean wall stress in an abdominal aortic aneurysm based on a loaded geometry: Effect of wall thickness

2006 ◽  
Vol 39 ◽  
pp. S327
Author(s):  
H. Yamada ◽  
Y. Hasegawa
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Thickness ◽  
Wall Stress ◽  
Simple Method ◽  
Geometry Effect ◽  
Abdominal Aortic ◽  
The Mean

Computational Modeling of the Effects of Transient Blood Flow Characteristics and Wall Thickness on the Rupture of Abdominal Aortic Aneurysm

2014 ◽  
Author(s):  
Pinaki Pal
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Thickness ◽  
Flow Model ◽  
Wall Stress ◽  
Flow Transition ◽  
Abdominal Aortic ◽  
Sst Model ◽  
Peak Wall Stress

Precise estimation of wall stress distribution within an abdominal aortic aneurysm (AAA) is clinically useful for prediction of its rupture. In this paper a computational fluid dynamic model incorporating two-way coupled fluid-structure interaction is employed to investigate the role of laminar-turbulent flow transition and wall thickness in altering the distribution and magnitude of wall stress in an AAA. Blood flow in axially symmetric aneurysm models governed by a compliant wall mechanics was simulated. Menter’s hybrid k-epsilon/k-omega shear stress transport (SST) model with a correlation-based transition model was used to capture laminar-turbulent transition in the blood flow. Realistic physiological transient boundary conditions were prescribed. The numerical model was validated against experimental data available from the literature. Fluid flow analysis showed the formation of recirculating vortices at the proximal end of the aneurysm after the peak systole which then, moved towards the distal end of the aneurysm along with the bulk flow and were dissipated eventually due to viscous effects. These vortices interacted with the aortic wall and led to local pressure rise. Von Mises stress distribution on the aneurysm wall and location of its peak value were computed and compared with those of a separate numerical simulation performed using a laminar viscous flow model. The predicted peak wall stress was found to be significantly higher for the SST model as compared to the laminar flow model. The location of maximum stress shifted more towards the posterior end of the aneurysm when laminar-turbulent flow transition was considered. In addition, a small reduction of 0.4 mm in wall thickness resulted in the elevation of peak wall stress by a factor of 1.4. The present study showed that capturing flow transition in an AAA is essential to accurate prediction of its rupture. The proposed numerical model provides a robust computational framework to gain more insight into AAA biomechanics and to accurately estimate wall stresses in realistic aneurysm configurations.

Wall Stress Studies of Abdominal Aortic Aneurysm in a Clinical Model

2001 ◽  
Vol 15 (3) ◽  
pp. 355-366 ◽  
Author(s):  
Mano J. Thubrikar ◽  
Jihad Al-Soudi ◽  
Francis Robicsek
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Clinical Model ◽  
Stress Studies ◽  
Abdominal Aortic

scholarly journals The Role of Geometric Parameters in the Prediction of Abdominal Aortic Aneurysm Wall Stress

2010 ◽  
Vol 39 (1) ◽  
pp. 42-48 ◽  
Author(s):  
E. Georgakarakos ◽  
C.V. Ioannou ◽  
Y. Kamarianakis ◽  
Y. Papaharilaou ◽  
T. Kostas ◽  
...  
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Geometric Parameters ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Abdominal Aortic Aneurysm Wall

Abstract 297: Segmental Aortic Stiffening is a Mechanism Driving Early Abdominal Aortic Aneurysm Pathogenesis

2014 ◽  
Vol 34 (suppl_1) ◽  
Author(s):  
Uwe Raaz ◽  
Alexander M Zöllner ◽  
Ryuji Toh ◽  
Futoshi Nakagami ◽  
Isabel N Schellinger ◽  
...  
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Aortic Wall ◽  
Ex Vivo ◽  
Wall Stress ◽  
Finite Elements Analysis ◽  
External Application ◽  
Abdominal Aortic ◽  
Aneurysm Growth ◽  
Aortic Stiffening

Stiffening of the aortic wall is a phenomenon consistently observed in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined. Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening (SAS) precedes aneurysm growth. Finite elements analysis (FEA)-based wall stress calculations reveal that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with reduced segmental stiffness of the AAA-prone aorta (due to equalized stiffness in adjacent aortic segments), reduced axial wall stress, decreased production of reactive oxygen species (ROS), attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, as well as attenuated apoptosis within the aortic wall. Cyclic pressurization of stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix (ECM) remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening. The present study introduces the novel concept of segmental aortic stiffening (SAS) as an early pathomechanism generating aortic wall stress and thereby triggering AAA growth. Therefore monitoring SAS by ultrasound might help to better identify patients at risk for AAA disease and better predict the susceptibility of small AAA to further growth. Moreover our results suggest that interventional mechanical stiffening of the AAA-adjacent aorta may be further tested as a novel treatment option to limit early AAA growth.

scholarly journals A Methodology for the Derivation of Unloaded Abdominal Aortic Aneurysm Geometry With Experimental Validation

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Santanu Chandra ◽  
Vimalatharmaiyah Gnanaruban ◽  
Fabian Riveros ◽  
Jose F. Rodriguez ◽  
Ender A. Finol
Keyword(s):  
Finite Element ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Stress Component ◽  
Wall Stress ◽  
Patient Specific ◽  
Element Analysis ◽  
Nodal Surface ◽  
Abdominal Aortic ◽  
Peak Wall Stress

In this work, we present a novel method for the derivation of the unloaded geometry of an abdominal aortic aneurysm (AAA) from a pressurized geometry in turn obtained by 3D reconstruction of computed tomography (CT) images. The approach was experimentally validated with an aneurysm phantom loaded with gauge pressures of 80, 120, and 140 mm Hg. The unloaded phantom geometries estimated from these pressurized states were compared to the actual unloaded phantom geometry, resulting in mean nodal surface distances of up to 3.9% of the maximum aneurysm diameter. An in-silico verification was also performed using a patient-specific AAA mesh, resulting in maximum nodal surface distances of 8 μm after running the algorithm for eight iterations. The methodology was then applied to 12 patient-specific AAA for which their corresponding unloaded geometries were generated in 5–8 iterations. The wall mechanics resulting from finite element analysis of the pressurized (CT image-based) and unloaded geometries were compared to quantify the relative importance of using an unloaded geometry for AAA biomechanics. The pressurized AAA models underestimate peak wall stress (quantified by the first principal stress component) on average by 15% compared to the unloaded AAA models. The validation and application of the method, readily compatible with any finite element solver, underscores the importance of generating the unloaded AAA volume mesh prior to using wall stress as a biomechanical marker for rupture risk assessment.

scholarly journals NUMERICAL ANALYSIS OF THE WALL STRESS IN ABDOMINAL AORTIC ANEURYSM: INFLUENCE OF THE MATERIAL MODEL NEAR-INCOMPRESSIBILITY

2012 ◽  
Vol 12 (01) ◽  
pp. 1250005 ◽  
Author(s):  
MAMADOU TOUNGARA ◽  
GREGORY CHAGNON ◽  
CHRISTIAN GEINDREAU
Keyword(s):  
Finite Element ◽  
Abdominal Aortic Aneurysm ◽  
Numerical Analysis ◽  
Aortic Aneurysm ◽  
Maximum Stress ◽  
Mechanical Response ◽  
Wall Stress ◽  
Model Complexity ◽  
Anisotropic Models ◽  
Abdominal Aortic

Recently, hyperelastic mechanical models were proposed to well capture the aneurismal arterial wall anisotropic and nonlinear features experimentally observed. These models were formulated assuming the material incompressibility. However in numerical analysis, a nearly incompressible approach, i.e., a mixed formulation pressure-displacement, is usually adopted to perform finite element stress analysis of abdominal aortic aneurysm (AAA). Therefore, volume variations of the material are controlled through the volumetric energy which depends on the initial bulk modulus κ. In this paper, an analytical analysis of the influence of κ on the mechanical response of two invariant-based anisotropic models is first performed in the case of an equibiaxial tensile test. This analysis shows that for the strongly nonlinear anisotropic model, even in a restricted range of deformations, large values of κ are necessary to ensure the incompressibility condition, in order to estimate the wall stress with a reasonable precision. Finite element simulations on idealized AAA geometries are then performed. Results from these simulations show that the maximum stress in the AAA wall is underestimated in previous works, committed errors vary from 26% to 58% depending on the geometrical model complexity. In addition to affect the magnitude of the maximum stress in the aneurysm, we found that too small value of κ may also affect the location of this stress.

scholarly journals Improving the Efficiency of Abdominal Aortic Aneurysm Wall Stress Computations

PLoS ONE ◽  
2014 ◽  
Vol 9 (7) ◽  
pp. e101353 ◽  
Author(s):  
Jaime E. Zelaya ◽  
Sevan Goenezen ◽  
Phong T. Dargon ◽  
Amir-Farzin Azarbal ◽  
Sandra Rugonyi
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Abdominal Aortic Aneurysm Wall
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