Layer-specific residual stretch changes along the human aorta: Effects of age, gender, and circumferential quadrant.

Regional distribution of circumferential residual strains in the human aorta according to age and gender

Our understanding of aortic biomechanics is customarily limited by lack of information on the axial residual stretches of the vessel in both humans and experimental animals that would facilitate the identification of its actual zero-stress state. The aim of this study was thus to acquire hitherto unreported quantitative knowledge of axial opening angle and residual stretches in different segments and quadrants of the human aorta according to age and gender. Twenty-three aortas were harvested during autopsy from the aortic root to the iliac bifurcation and were divided into ≥12 segments and 4 quadrants. Morphometric measurements were taken in the excised/curled configuration of rectangular strips considered to be under zero-stress using image-analysis software to study the axial/circumferential variation of axial opening angle, internal/external residual stretch, and thickness of the aortic wall. The measured data demonstrated: (1) an axial opening angle peak at the arch branches, decreasing toward the ascending and to a near-constant value in the descending thoracic aorta, and increasing in the abdominal aorta; (2) the variation of residual stretches resembled that of opening angle, but axial differences in external residual stretch were more prominent; (3) wall thickness showed a progressive diminution along the vessel; (4) the highest opening angle/residual stretches were found in the inner quadrant and the lowest in the outer quadrant; (5) the anterior was the thinnest quadrant throughout the aorta; (6) age caused thickening but greatly reduced axial opening angle/residual stretches, without differences between males and females.

Residual strains in ascending thoracic aortic aneurysms: The effect of valve type, layer, and circumferential quadrant

This study described the regional distribution of layer-specific residual deformations in fifteen human aortas collected during autopsy. Circumferentially and axially cut strips of standardized dimensions from the anterior quadrant of nine consecutive aortic levels were photographed to obtain the zero-stress state for the intact wall. The strips were then dissected into layers that were also photographed to obtain their zero-stress state. Changes in layer-specific opening angle, residual stretches, and thickness at each aortic level and direction were determined via image analysis. The circumferential and axial opening angles of the intima were ∼240 deg and ∼30 deg, respectively, throughout the aorta; those of the adventitia were ∼150 deg and -20 deg to 70 deg. The opening angles of the intact wall and media were similar in either direction. The circumferential residual stretches of the intima and the axial residual stretches of the media showed high values in the aortic arch, decreasing in the descending thoracic aorta and increasing toward the iliac artery bifurcation, while the axial residual stretches of the adventitia increased distally. The remaining residual stretches did not vary significantly with aortic level, suggesting an intimal role in determining circumferential, as well as medial and adventitial roles in determining axial residual stretches. We conclude that the tensile residual stretches released in the intima and media upon separation, and the compressive residual stretches released in the adventitia may moderate the inverse transmural stress gradients under physiologic loads, resulting from the >180 deg circumferential opening angle of the intact wall.

An improved analytical method to estimate three-dimensional residual stresses of the aorta

Opening angle and residual strain in a three-layered model of pig oesophagus

Time-course of axial residual strain remodeling and layer-specific thickening during aging along the human aorta

Variability in structure, morphology, and mechanical properties of the descending thoracic and infrarenal aorta around their circumference

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

Regional distribution of layer-specific circumferential residual deformations and opening angles in the porcine aorta

Data relating to residual deformations in human arteries are scarce. In this paper we investigate three-dimensional residual deformations for intact strips and for their separate layers from human aortas in their passive state. From 11 abdominal aortas with identified anamnesis, 16 pairs of rings and axial strips were harvested, and the rings cut open. After 16 h images of the resulting geometries were recorded, and the strips were separated into their three layers; after another 6 h images were again recorded. Image processing and analysis was then used to quantify residual stretches and curvatures. For each specimen histological analysis established that the intima, media and adventitia were clearly separated, and the separation was atraumatic. Axial in situ stretches were determined to be 1.196+/-0.084. On separation, the strips from the adventitia and media shortened (between 4.03 and 8.76% on average), while the intimal strips elongated on average by 3.84% (circumferential) and 4.28% (axial) relative to the associated intact strips. After separation, the adventitia from the ring sprang open by about 180 degrees on average, becoming flat, the intima opened only slightly, but the media sprang open by more than 180 degrees (as did the intact strip). The adventitia and intima from the axial strips remained flat, while the media (and the intact strip) bent away from the vessel axis. This study has shown that residual deformations are three dimensional and cannot be described by a single parameter such as 'the' opening angle. Their quantification and modeling therefore require consideration of both stretching and bending, which are highly layer-specific and axially dependent.

Effect of smooth muscle contraction on intramural strain distribution in rat thoracic aorta was investigated with residual strain considered. Short segments sliced from the aortas were cut radially to release residual strain in an aerated Krebs-Ringer solution (37 degrees C). Each segment opened up immediately to form an arc. Opening angle was measured at this point and after smooth muscle contraction and relaxation. The angle increased from 97 +/- 11 degrees (means +/- SE, n = 14) to 153 +/- 14 degrees with the contraction and decreased to 68 +/- 9 degrees with the relaxation, indicating increase in residual strain with smooth muscle contraction. Intramural strain distribution at various pressures was calculated from the opening angle and pressure-diameter relations of the aortas. Strain distribution was almost uniform at 55 mmHg under smooth muscle relaxation, whereas this pressure exceeded 200 mmHg because of the increase in residual strain and decrease in vessel diameter under smooth muscle contraction. These results suggest aortic smooth muscle may change its contractile state through myogenic response to keep intramural strain distribution uniform against temporary change in blood pressure and thus maintain mechanical homeostasis in the aortic wall.

The effects of viscoelasticity on residual strain in aortic soft tissues

Effects of aneurysm on the directional, regional, and layer distribution of residual strains in ascending thoracic aorta

Fitting mechanical properties of the aortic wall and individual layers to experimental tensile tests including residual stresses