Biomechanics of Arterial Smooth Muscle. : - Analyzing vascular adaptation of large elastic arteries using in vitro experiments and 3D finite element modeling.

Abstract:

A number of cardiovascular diseases (e.g. aortic aneurysm, aortic dissection and atherosclerosis) are associated with altered biomechanical properties in the vascular wall. This thesis studies vascular adaptation and its resulting alteration in biomechanical properties. Vascular adaptation refers to alterations in the vascular wall as a response to changes in its environment. This process can be examined through in vitro experiments on isolated blood vessels. Previous studies have shown that adaptation in arteries is induced by alterations in blood pressure. However, not much is known about the adaptation of smooth muscle cells and its resulting effects on the active tone. In order to verify previously obtained results on smooth muscle cell adaptation, in vitro experiments were conducted in this project. The in vitro experiments were conducted in a myograph on mice descending thoracic aorta. The experiments included a three-hour adaptation where the samples were contracted using an agonist at optimal stretch, or at a stretch lower than the optimal stretch. Concurring with the previous study, a decrease around 20% in active tone was observed after adaptation on low stretch. Based on the experimental data a constitutive framework was developed, which allows numerical studies on vascular adaptation of the active tone. Subsequently, the constitutive framework was implemented into the FEM software ABAQUS, and a thickwalled 3D artery was analyzed. By implementing the model in a FEM software, a platform for solving more complex boundary value problems has been created, and more challenging boundary conditions can be studied.