Mechanical properties of the aorta: a review.

Measurement and calculation of the mechanical properties of the aorta depend on a number of factors, including the degree of surgical invasion, vasomotor tone, tissue hydration, physical contact (i.e., the presence of a strain gauge), and the use of inside or outside diameter. Measurements on the aorta using angiography, transit-time determination, and echocardiographic techniques yield the most consistent values for parameters, including PVD, Ep, and Eo. Values of these parameters are listed in Table 7 and range from about 8 to 12.0% (PVD), 337 to 741 g/cm2 (Ep), and 0.33 to 3.6 x 10(6) dyn/cm2 (Eo) for human ascending aorta. Measurements made with invasive techniques tend to result in lower values of PVD and higher values of elastic moduli. Modeling studies focus on predicting the mechanical properties of a viscoelastic, anisotropic tube. Difficulty arises in modeling aorta because of hysteresis and the large deformations that are associated with physiologic loading patterns. Various forms of the strain-energy density function have been used to model relationships between stress and strain in three dimensions; however, they have limited value in understanding the mechanism of time-dependent stress transfer between fibrous and nonfibrous components found in aortic tissue. The ultimate utility of these models will include improved understanding of the physical basis of deformation of this important tissue and the mechanisms of premature failure associated with different disease processes.