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Abdominal Aortic Aneurysm development over time: Experimental evidence and constitutive modeling
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
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2010 (English)In: Proceedings of the 6th World Congress of Biomechanics, Springer, 2010Conference paper, Published paper (Refereed)
Abstract [en]

Abdominal Aortic Aneurysms (AAAs) are defined as a localized permanent dilatation of the infrarenal aorta at least 50 % of its normal diameter. AAAs are frequently diagnosed in the elderly male population and evaluating rupture risk is critically important as aneurysm rupture carries high mortality rates. Growth predictors might be helpful to assess AAA rupture risk and could therefore give a better graded indication for elective repair in order to reduce related mortality without unnecessarily increasing the rate of interventions. Factors associated with AAA growth are still limited but there are some evidence that higher initial AAA diameter is related to faster AAA expansion [1]. The initial dilatation is dependent on elastin degradation, but strength of the AAA is maintained by increased production of collagen. It has been suggested that rupture occurs when collagen production is insufficient to counteract load-bearing at high pressure [2].

AAA growth quantification

30 patients with infrarenal AAAs were included in this study. Criteria for inclusion were 1-year follow-up and availability of at least two high-resolution Computer Tomography-Angiography (CTA) scans. Consequently, 60 CT-A scans were systematically segmented, reconstructed and analyzed (A4research, VASCOPS GmbH), in order to investigate geometrical and mechanical factors likely to be correlated with AAA growth. Derived results were analyzed with an especially developed (automatic) analyzing schema (MatLab, The MathWorks), and the derived information aims at guiding the development of an analytical growth model for AAAs.

Constitutive Modeling

Collagen is a structural protein responsible for the mechanical strength, stiffness and toughness of biological tissues like skin, tendon, bone, cornea, lung and vasculature. In the present study we considered the enlargement of the aneurysm as a consequence of a pathological degradation and synthesis of collagen, i.e. malfunction of collagen turn-over. Consequently, the vascular wall is modeled by an (inert) matrix material representing the elastin, which is reinforced by a dynamic structure of bundles of collagen. Specifically, collagen is formed by a continuous stress-mediated process and deposited in the current configuration [3] and removed by a constant degradation rate. Finally the micro-plane concept [4] is used for the Finite Element implementation [5] of the constitutive model.

Results and conclusions

The quantitative description of AAA growth by examining patient follow-up data revealed novel insights into the natural history of this disease. Most interestingly not all portions of the AAA seem to enlarge, some might be stable or even shrink over time; a feature that has not yet been considered by models reported in the literature. The model proposed within this study has a

strong biological motivation and captures saline feature of AAA growth. Besides that, the micro-plane approach allows a straight forward FE implementation and preliminary results indicate its numerical robustness.

References

[1]

F.J.V. Schlösser, et al., J Vasc Surg, 47:1127–1133 2008.

[2]

E. Choke, et al., Eur.j.Vasc.endovasc.surg, 30(3):227-44 2005.

[3]

J.D.Humphrey, J Biomech Eng, 121:591–597 1999.

[4]

Z.P. Bazant and P.C. Prat, J Eng Mech, 113(7) 1050-1064 1987.

[5]

S. Federico and T.C Gasser, J R Soc Interface (in press)

Place, publisher, year, edition, pages
Springer, 2010.
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:kth:diva-89165ISBN: 978-3-642-14514-8 (print)OAI: oai:DiVA.org:kth-89165DiVA: diva2:502764
Conference
WCB 2010 - 6th World Congress on Biomechanics, Singapore, August 1-6 2010
Note
QC 20120418Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2012-04-18Bibliographically approved

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