Peeling and Torsional Shear of Porcine Thoracic Aorta

Abstract

Peeling of the aorta is a phenomenon with particular relevance for cardiovascular diseases like aortic dissection. There is initiation of a tear and then delamination between the medial layers. The tear can propagate into the body cavity or back into the artery creating a secondary flow. The tear can be circumferential, axial or in any direction. It usually occurs in the Thoracic aorta. Previous experimental studies have obtained the response under these conditions for human aorta samples in an attempt to obtain a peeling energy. Reasons for the initiation of the tear are currently poorly understood but insight into its propagation is a step forward. Measuring the peeling energy required for the tear to propagate improves our understanding of the condition. A technique is presented to measure the stretch undergone by the arms by optically tracking microspheres adhered to the arms. Accurate measurement of the stretch could lead to better peel energy calculations. Here, a protocol is described for measuring delamination energy in porcine aortas as a first step towards measuring delamination energy in healthy and diseased human aortas. Aortic tissue can undergo shearing deformation in physiological conditions like the twisting of the head for carotid artery. It is accepted that wall shear stresses control the production of many active molecules from the endothelial cells. Experimental data is needed for constitutive models which include the shearing behavior of the arterial wall. Unfortunately, most experimental data is related to extensional behavior even. As such torsional shearing of the aorta wall at high amplitudes as well as the effect of shear rate is looked into. Finally the dynamic response of the arterial wall is investigated. Arterial tissue is known to exhibit creep under constant load and relaxation under a constant strain. The arteries also undergo cyclic hemodynamic loading and procedures like balloon angioplasty require an understanding of the time dependent response. There is an initial investigation into the creep and relaxation behavior under torsional shear at high strains.