Experimental Investigation of Blood Flow in the Vertebral Artery Bifurcation

Background: The prone sites of cerebral atherosclerosis are located at the artery bifurcations of the Circle of Willis. Hemodynamic parameters of wall shear stress, vortex and secondary flow play an important role in the initiation, growth and rupture of the atherosclerosis, so investigate the hemodynamic characteristics will help us to understand the atherosclerosis better. Some numerical and experimental studies were carried out at the ICA and MCA bifurcation. However, none of them are focus on the VA bifurcation, where is also prone to atherosclerosis. Method: In this study, in order to investigate the hemodynamic characteristics in VA-BA bifurcation, the Particle Image Velocity (PIV) technique was applied to a scaled-up transparent patient-specific phantom, which is reconstructed from CT angiography (CTA) images and fabricated with rapid prototyping technique. A water-glycerin mixture was used to simulate the viscosity of blood and matched the refractive index of the flow phantom. The experiment was carried out under steady flow conditions of Re=300, Re=500. Results: The experimental results showed that a low wall shear stress and low fluid momentum region was in the bifurcation and right wall of BA. The wall shear stress in these areas was less than 0.4 Pa. Meanwhile, a strong secondary flow was observed at the bifurcate site. These results support the hypothesis that low shear stress(less than 0.4 Pa) is vital in the formation of plaque and thrombosis. Secondary flow at the downstream may rollback some blood through the high shear stress area repeatedly and causes the damage of the ingredients of blood; subsequently speed up the development of plaque.