Fluid-Structure Interaction of Large Viscoelastic Vessels Under Pulsatile Conditions

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Pejcic, Sonja
Aorta mechanics , Ultrasound , Constitutive laws , Cylindrical loading , Elastic properties , Viscoelastic behaviour
The current threshold diameter for aortic aneurysm repair is based on Laplace's law. However, aneurysms below this threshold have undergone dissection, while some larger aneurysms remain stable. An accurate understanding of how the dynamics of the aorta - particularly the fluid-structure interaction - relate to aneurysm progression is fundamental to streamlining clinical decisions. This thesis encompasses an experimental investigation into the response of compliant vessels to pulsatile flow for the purposes of properly characterizing the vessel-wall material properties. The structural deformation of, and flow field within, the compliant vessel were recorded using ultrasound imaging. The ultrasound data were then used to estimate the instantaneous elasticity of the vessel wall through a novel, dynamic model developed from a force analysis of a compliant vessel under two-dimensional (2D) stress. First, the instantaneous elasticity of a purely elastic, synthetic vessel with known properties was extracted using the 2D stress model and compared to Laplace's law. The 2D stress model was found to better predict the trend and magnitude of elasticity than the results from Laplace's law. Second, the instantaneous elasticity and dynamic viscoelastic properties of a porcine ascending aorta were calculated and compared to results from dynamic uniaxial testing. The instantaneous elasticity of the intact aorta matched well with uniaxial results, while the viscoelastic properties differed significantly between the cylindrical and uniaxial stress states.
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