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TECHNICAL PAPERS: Fluids/Heat/Transport

Fluid-Structure Interaction Effects on Sac-Blood Pressure and Wall Stress in a Stented Aneurysm

[+] Author and Article Information
Z. Li

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910

C. Kleinstreuer1

Department of Mechanical and Aerospace Engineering and Department of Biomedical Engineering, North Carolina State University, Raleigh, NC 27695-7910

1

E-mail: ck@eos.ncsu.edu

J Biomech Eng 127(4), 662-671 (Feb 17, 2005) (10 pages) doi:10.1115/1.1934040 History: Received August 16, 2004; Revised February 17, 2005

An aneurysm is a local artery ballooning greater than 50% of its nominal diameter with a risk of sudden rupture. Minimally invasive repair can be achieved by inserting surgically a stent-graft, called an endovascular graft (EVG), which is either straight tubular, curved tubular, or bifurcating. However, post-procedural complications may arise because of elevated stagnant blood pressure in the cavity, i.e., the sac formed by the EVG and the weakened aneurysm wall. In order to investigate the underlying mechanisms leading to elevated sac-pressures and hence to potentially dangerous wall stress levels and aneurysm rupture, a transient 3-D stented abdominal aortic aneurysm model and a coupled fluid-structure interaction solver were employed. Simulation results indicate that, even without the presence of endoleaks (blood flowing into the cavity), elevated sac pressure can occur due to complex fluid-structure interactions between the luminal blood flow, EVG wall, intra-sac stagnant blood, including an intra-luminal thrombus, and the aneurysm wall. Nevertheless, the impact of sac-blood volume changes due to leakage on the sac pressure and aneurysm wall stress was analyzed as well. While blood flow conditions, EVG and aneurysm geometries as well as wall mechanical properties play important roles in both sac pressure and wall stress generation, it is always the maximum wall stress that is one of the most critical parameters in aneurysm rupture prediction. All simulation results are in agreement with experimental data and clinical observations.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic of stented aneurysm with flow inlet and pressure outlet wave forms. (b) (i) Midplane view of a typical asymmetric aneurysm; (ii) artery neck (dashed line) projected onto the plane of maximum aneurysm cross section.

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Figure 2

Solution algorithm for fluid-structure interactions

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Figure 3

Comparison of sac pressure between numerical simulation and experimental data

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Figure 4

Wall stress distributions and flow fields in nonstented and stented AAAs (β=0.7,dA=6cm,tA=1mm,tEVG=0.2mm,EA=3.8MPa,EEVG=10MPa)

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Figure 5

(a) EVG lumen pressure, sac pressure, and aneurysm wall stress vary with time (asymmetry β=0.7, aneurysm diameter dA=6cm, wall thickness tA=1mm, tEVG=0.2mmEA=3.8MPa, EEVG=10MPa, VILT=0). (b) EVG lumen pressure, sac pressure, and EVG wall displacement vary with time (β=0.7,dA=6cm,tA=1mm,tEVG=0.2mm,EA=3.8MPa,EEVG=10MPa,VILT=0).

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Figure 6

Influence of aneurysm asymmetry on sac pressure and wall stress (dA=6cm,tA=1mm,tEVG=0.2mm,EA=4MPa,EEVG=10MPa,VILT=0)

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Figure 7

(a) Influence of aneurysm wall Young’s modulus on sac pressure and aneurysm wall stress (β=0.7,dA=6cm,tA=1mm,tEVG=0.2mm,EEVG=10MPa,VILT=0). (b) Influence of EVG wall Young’s modulus on sac pressure and aneurysm wall stress (β=0.7,dA=6cm,tA=1mm,tEVG=0.2mm,EA=4.0MPa,VILT=0)

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Figure 11

Influence of endoleak on sac pressure and aneurysm wall stress (β=1.0,dA=6cm,tA=1mm,EA=4MPa,EEVG=10MPa,VILT=0): (a) Static sac-volume changes; and (b) Transient sac-volume changes.

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Figure 8

Influence of aneurysm volumes on sac pressure and aneurysm wall stress (β=0.7,tA=1mm,tEVG=0.2mm,EA=4.0MPa,EEVG=10MPa,VILT=0)

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Figure 9

(a) Influence of aneurysm wall thickness on intrasac pressure and aneurysm wall stress (β=0.7,dA=6cm,tEVG=0.2mm,EA=4MPa,EEVG=10MPa,VILT=0). (b) Influence of aneurysm EVG thickness on intrasac pressure and aneurysm wall stress (β=0.7,dA=6cm,tA=1mm,EA=4MPa,EEVG=10MPa,VILT=0)

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Figure 10

Influence of ILT volume on the intrasac pressure and aneurysm wall stress (β=0.7,dA=6cm,tA=1mm,tEVG=0.2mm,EA=4MPa,EEVG=10MPa)

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