Mechanical properties of dilated human ascending aorta.

Dilation of the ascending aorta, associated with Marfan Syndrome, bicuspid aortic valve, or advanced age, may lead to aortic dissection and rupture. Mathematical models can be used to assess the relative importance of increased wall stresses and decreased strength in these mechanical failures. To obtain needed inputs for such models, mechanical properties of dilated human ascending aorta were measured in vitro. Specimens for opening angle, biaxial elastic, and uniaxial circumferential strength tests were cut from excised tissue obtained from 54 patients (age 18-81 years) undergoing elective aortic graft replacement surgery. Opening angle was significantly greater in patients older than 50 years (262 degrees + 76 degrees, n = 21) compared to younger patients (202 degrees +/- 70 degrees, n = 13). All biaxial elastic specimens (n = 40) exhibited nonlinear stress-strain behavior. Rapid increases in circumferential and axial stresses occurred at lower strains in the older patient group than in the younger. Mean strength was significantly lower in older patients (1.35 +/- 0.37 MPa, n= 14) than younger (2.04 +/- 0.46 MPa, n = 11, age <50 years). These changes in mechanical properties suggest that age may influence the risk of aortic dissection or rupture of dilated ascending aorta.