Microstructural and biomechanical alterations of the human aorta as a function of age and location

Abstract

While it is known that the aorta stiffens with location and age, little is known about the underlying mechanisms that govern these alterations. The purpose of this study was to investigate the relationship between the anisotropic biomechanical behavior and extracellular matrix microstructure of the human aorta and quantify how each changes with location and age. A total of 207 specimens were harvested from 5 locations (ascending n = 33, arch n = 38, descending n = 54, suprarenal n = 52, and abdominal n = 30) of 31 autopsy donor aortas (aged 3 days to 93 years). Each specimen underwent planar biaxial testing in order to derive quantitative biomechanical endpoints of anisotropic stiffness and compliance. Quantitative measures of fiber alignment and degree of fiber alignment were also generated on the same samples using a small-angle light scattering (SALS) technique. Circumferential and axial stiffening occurred with age and increased from the proximal to distal aorta, and the abdominal region was found to be more stiff than all others (p ≤ 0.006). Specimens from donors aged 61 and above were drastically more stiff than younger specimens (p < 0.001) and demonstrated greater circumferential compliance and axial stiffening (p < 0.001). Fiber direction for all ages and locations was predominantly circumferential (p < 0.001), and the degree of fiber alignment was found to increase with age (p < 0.001). Our results demonstrate that the aorta becomes more biomechanically and structurally anisotropic after age 60; with significant changes occurring preferentially in the abdominal aorta, these changes may play an important role in the predisposition of disease formation (e.g., aneurysm) in this region with age.

Local mechanical properties of human ascending thoracic aneurysms

“…6, Table 3 and 5). This is in agreement with the the existing literature on the effect of aging [10][11][12]29] which found that the healthy thoracic aorta stiffened progressively with age with substantial stiffening occurring between patients aged 30-60 and those over the age of 60. At 55 years old, Patient 6 would be in the younger group while the remainder of the cohort had a mean age of 76.6 yrs.…”

Mechanical identification of layer-specific properties of mouse carotid arteries using 3D-DIC and a hyperelastic anisotropic constitutive model

“…Though it cannot be generalized based on a single example, this result brings some comments. From a global point of view the overall anisotropy of the artery, with the circumferential direction being stiffer, is typical for arteries in general, and is in qualitative agreement with previous studies, even though the constitutive models were different (Sutton et al 2008;Gleason et al 2008;Haskett et. al.…”

Prefailure and Failure Mechanics of the Porcine Ascending Thoracic Aorta: Experiments and a Multiscale Model

“…[15]). Previous studies have shown that collagen fibers within the arterial media have strong preferential orientation in the circumferential direction (X hh ) while some percentage of fibers are mainly oriented in the axial direction (X zz ) and even smaller percentage in the radial direction (X rr ) [19][20][21][22][23]. Based on those studies, the average orientation for collagen fiber networks in the media [X hh X zz ] was extrapolated to be [0.62 0.37] [20].…”