THE EFFECTS OF PHYSIOLOGICAL FLOW WAVEFORM ON WALL SHEAR STRESS IN CAROTID BIFURCATION MODEL

Numerical models of carotid bifurcation were constructed using a combination of tuning-fork bifurcation and straight or curved common carotid. The different inlet velocity profiles of the common carotid were generated for Bloch flow waveform and Holdsworth flow waveform, respectively. The effects of the different flow waveform for the common carotid on Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) of carotid bifurcation were studied by CFD method. The results show that the physiological flow waveform of curved common carotid has a significant effect on OSI. In particular, the OSI on the outer walls of carotid sinus and external carotid becomes higher in the inward-curved common carotid for Holdsworth flow waveform. But, in both cases of low WSS and high OSI, the effects of flow waveforms are smaller than those of the curved common carotid. The study reveals that the exact knowledge of the physiological flow waveform, vascular geometry and inlet velocity profile is important for hemodynamic numerical simulation of artery bifurcation.     

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.