Effect of Aneurysm and Bicuspid Aortic Valve on Layer-Specific Ascending Aorta Mechanics.

Background: Previous studies have not examined the participation of intimal, medial, and adventitial layers in providing mechanical strength to the ascending thoracic aortic aneurysm (ATAA) wall compared with the nonaneurysmal aorta. In this study we compared the mechanical properties of intact wall and its layers among ATAAs and nonaneurysmal aortas, with explicit consideration of the effects of valve morphology; that is, bicuspid aortic valve (BAV) versus tricuspid aortic valve (TAV), and aortic quadrant.

Methods: Whole ATAAs were taken from patients undergoing elective repair and nonaneurysmal aortas from age-matched autopsy subjects.

Effects of aneurysm on the mechanical properties and histologic structure of aortic sinuses.

Background: Aortic root aneurysms are relatively uncommon but their rupture is a detrimental event with acute hemodynamic compromise and high mortality, and there are few available data on their mechanical properties, although aneurysm rupture occurs when hemodynamic stresses exceed wall strength. This study aimed to fill this gap by examining the effect of aneurysm on the mechanical and structural properties of aortic sinuses.

Methods: Sinus tissue was procured from 16 aneurysmal patients during surgical repair and from 18 age-matched nonaneurysmal autopsy subjects, and grouped by age (young versus old), region (left versus right versus noncoronary), and direction (circumferential versus longitudinal).

Biomechanical properties and histological structure of sinus of Valsalva aneurysms in relation to age and region.

Information on the biomechanical properties of aortic root aneurysms that would facilitate our understanding of their rupture modes is currently unavailable. In this study, whole-thickness wall specimens from aortic root aneurysms were studied in vitro so as to compare the biomechanical properties with gross histomorphology and composition, in relation to age, region, and direction. The stress-strain relationship was determined under uniaxial loading conditions and characterized by the Fung-type material model in terms of optimized material constants; failure properties were recorded.

Effect of layer heterogeneity on the biomechanical properties of ascending thoracic aortic aneurysms.

This study addressed layer-specific differences in the biomechanical response of ascending aortic aneusysms, obtained from patients during graft replacement. Tensile tests were conducted on pairs of (orthogonally directed) intimal, medial, and adventitial strips from the anterior, posterior, and two lateral quadrants. The experimental data were reduced by the Fung-type model, affording appropriate characterization of the material properties.

Time course of flow-induced adaptation of carotid artery biomechanical properties, structure and zero-stress state in the arteriovenous shunt.

Numerous studies have provided evidence of diameter adaptation secondary to flow-overload, but with ambiguous findings vis à vis other morphological parameters and information on the biomechanical aspects of arterial adaptation is rather incomplete. We examined the time course of large-artery biomechanical adaptation elicited by long-term flow-overload in a porcine shunt model between the carotid artery and ipsilateral jugular vein. Post-shunting, the proximal artery flow was doubled and retained so until euthanasia (up to three months post-operatively), without pressure change.

Differential histomechanical response of carotid artery in relation to species and region: mathematical description accounting for elastin and collagen anisotropy.

The selection of a mathematical descriptor for the passive arterial mechanical behavior has been long debated in the literature and customarily constrained by lack of pertinent data on the underlying microstructure. Our objective was to analyze the response of carotid artery subjected to inflation/extension with phenomenological and microstructure-based candidate strain-energy functions (SEFs), according to species (rabbit vs. pig) and region (proximal vs.

Biomechanical response of ascending thoracic aortic aneurysms: association with structural remodelling.

Ascending thoracic aortic aneurysms (ATAA) were resected from patients during graft replacement and non-aneurysmal vessels during autopsy. Tissues were histomechanically tested according to region and orientation, and the experimental recordings reduced with a Fung-type strain--energy function, affording faithful biomechanical characterisation of the vessel response. The material and rupture properties disclosed that ATAA and non-aneurysmal aorta were stiffer and stronger circumferentially, accounted by preferential collagen reinforcement.

Local hemodynamics and intimal hyperplasia at the venous side of a porcine arteriovenous shunt.

Venous anastomotic intimal hyperplasia (IH) observed in the arteriovenous shunt (AVS) has been associated with disturbed hemodynamics. This study aims to correlate hemodynamics with wall histology and wall mechanics by examining the flow field in AVS with computational fluid dynamics using experimental data taken from in vivo experiments. Input data to the computational model were obtained in vivo one month after AVS creation; adjacent vessels were submitted to histological and mechanical examination.

Biomechanical, morphological and zero-stress state characterization of jugular vein remodeling in arteriovenous fistulas for hemodialysis.

While the role of hemodynamic variables on the development of intimal hyperplasia in arteriovenous fistulas for hemodialysis has been examined, less is known about the intramural biomechanical factors. In this study, arteriovenous fistulas were created by implantation of e-PTFE grafts between carotid artery and jugular vein in healthy pigs. In vivo recordings exhibited a three-fold pressure and flow elevation in grafted veins after fistula creation, remaining so until sacrifice.

Ascending thoracic aortic aneurysms are associated with compositional remodeling and vessel stiffening but not weakening in age-matched subjects.

Objective: We sought to examine in age-matched subjects the biomechanical and compositional remodeling associated with ascending thoracic aortic aneurysms according to region and direction.

Methods: Whole, fresh, degenerative ascending thoracic aortic aneurysms were taken from 26 patients (age, 69 +/- 2 years; maximum aortic diameter, 5.9 +/- 0.

Regional and directional variations in the mechanical properties of ascending thoracic aortic aneurysms.

This study aimed to assess regional and directional differences in the mechanical properties of ascending thoracic aortic aneurysms (ATAA). Whole fresh ATAA were taken from twelve patients, undergoing elective surgical repair, and cut into tissue specimens. These were divided into groups according to direction and region, and subjected to uniaxial testing beyond rupture.