Over-Wrapping of the Aortic Wall with an Elastic Extra-Aortic Wrap Results in Luminal Creasing

Abstract

Elastic extra-aortic wrapping is a potential non-pharmacological way to improve aortic compliance and treat isolated systolic hypertension associated with a stiffened aorta. We aimed to use computer simulations to re-evaluate whether there is aortic shape distortion in aortic wrapping to achieve greater elasticity of the wrapped aortic segment. Non-linear transient numerical analysis based on an idealized hyper-elastic single-layered aorta model was performed to simulate the force/displacement regimes of external aortic wrapping. Pressure-displacement relationships were used to establish model aortic wall distensibilities of 4.3 and 5.5 (10−3 mmHg−1). A physiological pulsatile lumen pressure was employed to estimate the potential improvements in aortic distensibility by compression forces representing elastic aortic wrapping. In the less distensible model of the aortic wall there was increased systolic expansion in the wrapped segment. We found a risk of creasing of the aortic luminal wall with wrapping. Sufficient unloading of a thick and elastic aortic wall to induce increased compliance, as observed in elastic wrapping, is associated with the potential risk of over compression and folding (creasing) inside the lumen.

Computational evaluation of an extra-aortic elastic-wrap applied to simulated aging anisotropic human aorta models

“…Our anisotropic constitutive model considering collagen fiber orientation confirmed earlier results of shape distortion upon threshold compression forces 16 . We conclude that to achieve further constriction, the circular aortic cross section will become distorted.…”

“…We confirm via our simulations the in-vivo results reported by Iliopoulos 7 and Gillies et al . 8 that show stiff aortas are more likely to be treated effectively with elastic wrapping compared to the young, compliant, native aorta.Our anisotropic constitutive model considering collagen fiber orientation confirmed earlier results of shape distortion upon threshold compression forces 16 . We conclude that to achieve further constriction, the circular aortic cross section will become distorted.…”

“…Note that compression forces higher than 12000 Pa applied to the ‘elderly’ stiffness model lead to buckling or shape deformation of the aortic model. Our ‘middle aged’ aortic stiffness model showed creasing of the aortic wall at compression forces greater than 14000 Pa. As discussed in our previous study 16 , increasing compression forces beyond a stiffness-dependent threshold can result in luminal creasing.

Figure 3Normalised luminal cross-section increases during systole plotted versus radial compression as a result of elastic wrapping. Stiffness models ‘middle aged’ (AD = 6 [10 −3 mmHg −1 ]) and ‘elderly’ population (AD = 1 [10 −3 mmHg −1 ]) are contrasted.

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The influence of aortic stiffness on carotid stiffness: computational simulations using a human aorta carotid model

“…The geometry was discretized with three-dimensional hexahedral elements to create a computational mesh with 36 158 elements in total [ 19 ]. This mesh condition was then re-examined and appeared to be responsive to variable simulation parameters.…”

Computational Evaluation for Age-Dependent Material Nonlinear Behavior of Aortic Wall Tissue on Abdominal Aortic Aneurysms

“…Therefore, the mechanical analysis in identifying the precise material behavior and degradation of abdominal aortic properties according to the major factors should be performed in order to solve these problems. Experimental and computational analyses of the extracted tissues from carcasses, cadavers, and patients have been conducted to identify the precise material behaviors and properties based on various factors, such as vascular location [3][4][5][6][7], layer [8][9][10][11], diameter [12], and smoking preference [5] in leading overseas research institutions for many decades [13][14][15][16][17].…”