Understanding the biomechanics of Windkessel arteries is an important task as structural remodeling of large arteries is in the background of several pathological processes, such as pathologic afterload of the left ventricle, high arterial pressure, filtration disturbances, atherosclerosis, aneurysms.
In my thesis in vivo behavior of Windkessel arteries was studied on 13 male rabbits, weighing 3-3,5 kg. In these experiments the movements of the aorta were recorded after open chest surgery performed in Nembutal anesthesia. A cannula was introduced into the observed aortic segment to record pulsatile blood pressure curves (BIOPAC, Experimetria pressure head and software). Blood flow was recorded using a Transonic ultrasonographic head put around the aorta. The pulsatile movements of the vessel were recorded by a video-microscopic camera. 3D and 2D loops were constructed and analyzed using corresponding values of these parameters.
Transversal rings were cut from the same segments of the thoracic aorta and fixed among holders with 3.0 mm free initial lengths. After incubating the strips in nKR, NE containing and Ca-free medium (as a sum 3x12 samples) they were sequentially stretched by 400 micrometer unit steps. (One step contained of a 0.1 sec length extension and of a following 2 minutes stress relaxation.) Force was continuously recorded until full rupture. Stress values were computed using measured forces, and using the Maxwell model, curve-fitting based on the least squares method, the serial and parallel elastic moduli as well as the viscotic modulus were computed. Some parameters were compared with the values of the Kelvin-Voigt model.
Results and conclusion
The 2D and 3D pulsatile loops revealed that viscosity is an important factor in vivo in the aortic wall. On the loops, in addition to the mostly viscous and mostly elastic sections, several times a section characterized by active shortening could be distinguished. Our 3D loops many times demonstrated a phase delay of the flow-pulse in comparison with the other two parameters. At the tensile strength measurement of transversal strips, results of the two models did not much differ. At present time we cannot declare which of them is more correct to describe the biomechanical properties of the aortic wall.