Quantification of regional differences in aortic stiffness in the aging human

Abstract

There has been a growing awareness over the past decade that stiffening of the aorta, and its attendant effects on hemodynamics, is both an indicator and initiator of diverse cardiovascular, neurovascular, and renovascular diseases. Although different clinical metrics of arterial stiffness have been proposed and found useful in particular situations, there remains a need to understand better the complex interactions between evolving aortic stiffness and the hemodynamics. Computational fluid–solid-interaction (FSI) models are amongst the most promising means to understand such interactions for one can parametrically examine effects of regional variations in material properties and arterial geometry on local and systemic blood pressure and flow. Such models will not only increase our understanding, they will also serve as important steps towards the development of fluid–solid-growth (FSG) models that can further examine interactions between the evolving wall mechanics and hemodynamics that lead to arterial adaptations or disease progression over long periods. In this paper, we present a consistent quantification and comparison of regional nonlinear biaxial mechanical properties of the human aorta based on 19 data sets available in the literature and we calculate associated values of linearized stiffness over the cardiac cycle that are useful for initial large-scale FSI and FSG simulations. It is shown, however, that there is considerable variability amongst the available data and consequently that there is a pressing need for more standardized biaxial testing of the human aorta to collect data as a function of both location and age, particularly for young healthy individuals who serve as essential controls.

Decreased Elastic Energy Storage, Not Increased Material Stiffness, Characterizes Central Artery Dysfunction in Fibulin-5 Deficiency Independent of Sex

“…They showed that, under free extension conditions, the ATA consistently exhibits the highest axial stretch within each group of patients with no reported differences between the two sexes. Indeed, Roccabianca et al [24] compared biaxial properties of human ATA, DTA, and IAA from young, middle-aged, and older subjects based on data from the literature. Strikingly, they also found that, within each age group, the ATA shows the highest axial extensibility, thus supporting the uniqueness of its biomechanical properties.…”

“…Moreover, defects in, damage to, or degradation of elastic fibers play fundamental roles in central arterial stiffening [20][21][22], hence there is strong motivation to study the role of fibulin-5 in central artery stiffness. Of course, rigorous quantification of arterial mechanics necessitates using consistent methods of biaxial testing and data analysis that focus on near physiologic conditions [23,24], This paper addresses these multiple needs by comparing, for the first time, the passive biaxial mechanical properties of five central arteries from male and female wild-type (Fbln5^l+) and fibulin-5 deficient (Fbln5~ ~) mice: the ascending thoracic aorta (ATA), proximal descending thoracic aorta (DTA), suprarenal ab dominal aorta (SAA), infrarenal abdominal aorta (IAA), and com mon carotid artery (CCA). Results are presented in terms of multiple mechanical metrics, including best-fit values of model parameters for a nonlinear anisotropic constitutive relation for wall stress, values of linearized stiffness computed at physiologi cal loads, and the energy stored and dissipated during in vitro cyclic loading.…”

Heart Rate Dependency of Large Artery Stiffness

“…Our BP correction method using mathematical modeling incorporates the nonlinear relationship between BP and cfPWV, and it is based on an assumed exponential P-A relationship. 23 However, the exact exponential nature of this relationship can be debated, as other descriptives 47 as well as P-A relationship based on the actual wall constituents [48][49][50] have also been proposed. Nevertheless, the exponential relationship provides an acceptable compromise between accuracy and practical use.…”

Human thoracic and abdominal aortic aneurysmal tissues: Damage experiments, statistical analysis and constitutive modeling

“…We used a statistical approach to determine the significance of differences among the model parameters fitted to healthy descending thoracic tissue samples (from Weisbecker et al, 2012) to those from diseased ascending thoracic samples. We know that there are differences in the mechanical properties between healthy ascending and descending thoracic aortic tissues (Roccabianca et al, 2014), but because of the samples available, we assume that we can still capture trends in the changes of model parameters due to aneurysm growth.…”