Measuring and modeling patient-specific distributions of material properties in abdominal aortic aneurysm wall
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Both the clinically established diameter criterion and novel approaches of computational finite element (FE) analyses for rupture risk stratification of abdominal aortic aneurysms (AAA) are based on assumptions of population-averaged, uniform material properties for the AAA wall. The presence of inter-patient and intra-patient variations in material properties is known, but has so far not been addressed sufficiently. In order to enable the preoperative estimation of patient-specific AAA wall properties in the future, we investigated the relationship between non-invasively assessable clinical parameters and experimentally measured AAA wall properties. We harvested n = 163 AAA wall specimens (n = 50 patients) during open surgery and recorded the exact excision sites. Specimens were tested for their thickness, elastic properties, and failure loads using uniaxial tensile tests. In addition, 43 non-invasively assessable patient-specific or specimen-specific parameters were obtained from recordings made during surgery and patient charts. Experimental results were correlated with the non-invasively assessable parameters and simple regression models were created to mathematically describe the relationships. Wall thickness was most significantly correlated with the metabolic activity at the excision site assessed by PET/CT (ρ = 0.499, P = 4 × 10−7) and to thrombocyte counts from laboratory blood analyses (ρ = 0.445, P = 3 × 10−9). Wall thickness was increased in patients suffering from diabetes mellitus, while it was significantly thinner in patients suffering from chronic kidney disease (CKD). Elastic AAA wall properties had significant correlations with the metabolic activity at the excision site (PET/CT), with existent calcifications, and with the diameter of the non-dilated aorta proximal to the AAA. Failure properties (wall strength and failure tension) had correlations with the patient’s medical history and with results from laboratory blood analyses. Interestingly, AAA wall failure tension was significantly reduced for patients with CKD and elevated blood levels of potassium and urea, respectively, both of which are associated with kidney disease. This study is a first step to a future preoperative estimation of AAA wall properties. Results can be conveyed to both the diameter criterion and FE analyses to refine rupture risk prediction. The fact that AAA wall from patients suffering from CKD featured reduced failure tension implies an increased AAA rupture risk for this patient group at comparably smaller AAA diameters.
KeywordsAbdominal aortic aneurysm Diameter criterion Finite elements Material properties Wall thickness Wall strength
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- CKD-MBD Work Group (2009) KDIGO clinical practice guideline for the diagnosis, evaluation, prevention, and treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD). Kidney disease: improving global outcomes (kdigo) CKD-MBD work group. Kidney Int Suppl 113:1–130Google Scholar
- Folco EJ, Sheikine Y, Rocha VZ, Christen T, Shvartz E, Sukhova GK, Di Carli MF, Libby P (2011) Hypoxia but not inflammation augments glucose uptake in human macrophages: implications for imaging atherosclerosis with 18fluorine-labeled 2-deoxy-d-glucose positron emission tomography. J Am Coll Cardiol 58(6): 603–614CrossRefGoogle Scholar
- Fung YC (1993) Biomechanics—mechanical properties of living tissues, 2nd edn. Springer, New YorkGoogle Scholar
- Holzapfel GA (2000) Nonlinear solid mechanics: a contiuum approach for engineering. Wiley, ChichesterGoogle Scholar
- Raghavan ML, Lin K, Ramachandran M, Nadereishvili A, Amelon R, Lu J (2011b) Planar radial extension for constitutive modeling of anisotropic biological soft tissues. Int J Struct Changes Sol 3(2): 23–31Google Scholar
- Reeps C, Essler M, Pelisek J, Seidl S, Eckstein HH, Krause BJ (2008) Increased 18F-fluorodeoxyglucose uptake in abdominal aortic aneurysms in positron emission/computed tomography is associated with inflammation, aortic wall instability, and acute symptoms. J Vasc Surg 48(2): 417–423CrossRefGoogle Scholar
- Reeps C, Gee MW, Maier A, Pelisek J, Gurdan M, Wall WA, Mariss J, Eckstein HH, Essler M (2009) Glucose metabolism in the vessel wall correlates with mechanical instability and inflammatory changes in a patient with a growing aneurysm of the abdominal aorta. Circ Cardiovasc Imaging 2(6): 507–509CrossRefGoogle Scholar
- The UK Small Aneurysm Trial Participants with Brown LC and Powell JT (1999) Risk factors for aneurysm rupture in patients kept under ultrasound surveillance. Ann Surg 230(3):289–297 (2006)Google Scholar
- Wall WA, Gee MW (2010) Baci: a parallel multiphysics simulation environment. Technical report, Institute for Computational Mechanics, Technische Universität MünchenGoogle Scholar