ANISOTROPY AND CHANGES IN MECHANICAL PROPERTIES IN AAA AND NON-AAA WALL TISSUE

Abstract

Abdominal aortic aneurysm (AAA), and other cardiovascular disease ar likely associated with changes in mechanical properties of the aortic wall These properties depend mainly on the composition of the aortic wall. Since wall composition changes when AAA are present, it appears probable tha mechanical properties of AAA wall tissue may differ from those of non AAA wall tissue. The objective of this study was to evaluate the differences between AAA and non-AAA wall tissue regarding ultimate strength (σu and modulus of elasticity (E) in the circumferential (cir) and longitudina (Ion) directions. Tensile strength tests were performed in tissue samples obtained from patients during autopsy (non-AAA). or surgery (AAA), using an INSTRON tensile testing machine (model 1122. Instron Corp., Canton MA). Strain rate was 10 mm/min, and sectional area was calculated assuming constant volume and Poisson's ratio of 0.50. Curve fittings were done on a PC using Microsoft ®Excel 97. Results: 22 non-AAA samples from 11 patients, age 59.4 ± 9.8 yr (mean ± SD), and 44 AAA samples from 22 patients, age 58.8 ± 12.3 yr (mean ± SD) were tested. For non-AAA tissue σlon = 1702 ± 57 kPa, σcir = 940 79 kPa, Elon = 1680 ± 76 kPa. Ecir = 1055 ± 59 kPa. For AAA tissue σlon = 1143 ± 67 kPa, σcir = 66 ± 62 kPa, Elon = 1356 ± 87 kPa, Eci = 966 ± 46 kPa. (See Figure). Both σ and E were significantly lower (< 0.05) in AAA tissue than in non AAA tissue. Furthermore, both σ and E were significantly lower in the cir than in the lon direction (p < 0.05). in non-AAA and in AAA tissue.FigureIn conclusion, these experiments show evidence that ultimate strength and modulus of elasticity are significantly reduced in AAA wall tissue. In addition, these properties are significantly lower in the circumferential direction than in the longitudinal direction for both AAA and non-AAA tissue. Therefore, anisotropy and differences between non-AAA and AAA tissue should be taken into account to optimize computational models of AAA wall stress and deformation.