SYNERGY OF WALL SHEAR STRESS AND CIRCUMFERENTIAL STRESS IN STRAIGHT ARTERIES

The Wall Shear Stress （WSS） generated by blood flow and Circumferential Stress （CS） driven by blood pressure have been thought to play an important role in blood flow-dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis. The WSS and CS in straight arteries were calculated by measuring the blood pressure, center-line velocity, wall thickness, and radius of vessels. The WSS and CS in the time domain were then decomposed into the amplitude and phase in the frequency domain. The CS amplitude to the WSS amplitude ratio （referred as stress ampli tude ratio, Zs ） and the phase difference between the CS and the WSS （referred as stress phase difference, SPA） in the fre quency domain were calculated to characterize the synergy of the CS and WSS. Numerical results demonstrated that the CS is not in phase with the WSS, a time delay in the time domain or a stress phase difference in the frequency domain between the WSS and the CS exists. Theoretical analysis demonstrated that the Zs and SPA are primarily determined by the local fac tors （blood viscosity, local inertial effects, local geometry, loeal elasticity） and the input impedance of whole downstream arterial beds. Because the arterial input impedance has been shown to reflect the physiological and pathological states of whole downstream arterial beds, the stress amplitude ratio Zs and stress phase difference SPA would be thought to be the appropriate indices to reflect the effects of states of whole downstream arterial beds on the local blood flow dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis.

Numerical Determination of the Circumferential Residual Stress of Porcine Aorta by Pulling-Back Method

Residual stress is very important for the study of cardiovascular-relevant issues,such as assessing the vulnerability of atherosclerosis and aneurysm.In this paper,the circumferential residual stress of porcine aorta was characterized by combining ex vivo experiments with numerical studies.In the experiments,porcine aortic rings were prepared and cut open,and the cross sections of the opened aortic rings were extracted to construct finite element models.The 5-parameter Mooney-Rivlin model was chosen to describe the tensile mechanical behavior of the aorta.In numerical studies,based on the finite element models and hyperelastic material model,a pulling-back displacement was applied to reclose the models of the opened aortic rings,and the equivalent circumferential residual stress to the pre-opened aorta was analyzed.The results showed that the circumferential residual stress of the aorta generally decreased from the proximal to the distal ends,and the residual stresses of the aortic rings close to the distal end did not show a great difference.This work provides an improved understanding of the residual stress distribution in aorta and may be used as a more realistic initial condition for future stress analysis of the arterial tissue.