Mechanical properties and constitutive modeling of the human arteriovenous fistula aneurysm

The arteriovenous fistula (AVF), a surgically created connection between an artery and a vein, remains the gold standard for vascular access in patients undergoing chronic hemodialysis. The fistula is most commonly created on the upper limb, where, for example, the cephalic vein and radial or brachial artery can be used. Although AVF is the most common method used for vascular access in hemodialysis, its performance remains vulnerable to multiple sources of potential failure. An arteriovenous fistula aneurysm (AVFA) in particular is one of the most common pathologies that develops in the vein segment of the anastomosis. The causes leading to AVFA formation are not yet fully understood, nevertheless both the remodeling process and tissue scarring induced by repeated cannulation of the vein contribute to its development. With this study, we wish to contribute to expanding our knowledge of AVFA biomechanics. Samples of healthy cephalic veins and aneurysmatic AVFs were collected from human donors. Uniaxial tensile tests in two perpendicular directions were carried out to determine their mechanical response. A significant decrease in the initial Young’s elastic modulus and anisotropy was observed in the AVFA group. Histological analysis of the samples showed a degradation of the elastic component and a disorganization of the collagen and VSMC. A 4-fiber-family hyperelastic anisotropic constitutive model of the exponential type was used in the nonlinear regression of the experimental data. The resulting constitutive models led to a good correspondence between the data and predictions. The obtained estimates of the constitutive parameters can be used in future fluid-structure interaction analyses aimed at computational simulations of AVF and AVFA hemodynamics.