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Research Papers

# Intrasac Pressure Changes and Vascular Remodeling After Endovascular Repair of Abdominal Aortic Aneurysms: Review and Biomechanical Model Simulation

[+] Author and Article Information
S. T. Kwon

Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218

J. E. Rectenwald

Department of Surgery, and Department of Radiology, University of Michigan, Ann Arbor, MI 48109

S. Baek1

Department of Mechanical Engineering, 2500 Engineering Building, Michigan State University, East Lansing, MI 48824-1226sbaek@egr.msu.edu

1

Corresponding author.

J Biomech Eng 133(1), 011011 (Dec 23, 2010) (9 pages) doi:10.1115/1.4003134 History: Received October 25, 2010; Revised November 15, 2010; Posted November 29, 2010; Published December 23, 2010; Online December 23, 2010

## Abstract

In this paper, we review existing clinical research data on post-endovascular repair (EVAR) intrasac pressure and relation with abdominal aortic aneurysm (AAA) size changes. Based on the review, we hypothesize that intrasac pressure has a significant impact on post-EVAR AAA size changes, and post-EVAR remodeling depends also on how the pressure has changed over a period of time. The previously developed model of an AAA based on a constrained mixture approach is extended to include vascular adaptation after EVAR using an idealized geometry. Computational simulation shows that the same mechanism of collagen stress-mediated remodeling in AAA expansion induces the aneurysm wall to shrink in a reduced sac-pressure after post-EVAR. Computational simulation suggests that the intrasac pressure of $60 mm Hg$ is a critical value. At this value, the AAA remains stable, while values above cause the AAA to expand and values below cause the AAA to shrink. There are, however, variations between individuals due to different cellular sensitivities in stress-mediated adaptation. Computer simulation also indicates that an initial decrease in intrasac pressure helps the AAA shrink even if the pressure increases after some time. The presented study suggests that biomechanics has a major effect on initial adaptation after EVAR and also illustrates the utility of a computational model of vascular growth and remodeling in predicting diameter changes during the progression and after the treatment of AAAs.

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## Figures

Figure 1

Intrasac pressure with respect to time varying the final pressure P∞ for a constant k=1/40

Figure 2

Best-fit pressure curves after EVAR using clinical data from Ellozy (11) compared with the pressure-time curve using the control values for simulation (dotted line)

Figure 3

AAA diameter growth and thickness change before EVAR, varying cell sensitivity parameters

Figure 4

AAA radius with respect to axial length showing growth of AAA before EVAR (left) and shrinking after EVAR (right)

Figure 5

AAA diameter, thickness, the circumferential component, and the axial component of the stress at the middle point of the wall with respect to time for different final intrasac pressure P∞

Figure 6

AAA diameter and thickness with respect to time, showing the effects of changing cell sensitivity

Figure 7

Changes of AAA diameter and thickness for the intrasac pressure curves obtained from the shrinking and stable aneurysms in Ellozy (11)

Figure 8

AAA pressure and diameter with respect to time, demonstrating the affect of making the intrasac pressure inconsistent

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