# An Assisted Numerical Simulation Diagnosis Method for Atherosclerosis Based on Hemodynamics
## 3 Calculation Results and Analysis
### Analysis of Lesion-Susceptible Artery Bifurcation Sites  
Clinical studies found that carotid bifurcation vessels are areas with a high incidence of atherosclerosis. The simulation results of shear stress distribution in a healthy carotid bifurcation vessel during one cardiac cycle are shown in Figure 8. The figure shows that shear stress varied with the input pulse signal and was uniformly distributed at the beginning of the cardiac cycle (\(t\) = 0-0.15 s) at below 5 Pa. Shear stress rose rapidly when the signal reached the peak at \(t\) = 0.15 s, and shear stress further increased to the maximum after the peak. The sites with the maximum tangential stress on the vessel wall surface below 10 Pa at this moment accounted for 70%. A flow separation zone with lower flow velocity and shear stress levels than other sites was observed on both sides of the carotid bifurcation site. The fluid characteristics in this zone did not change substantially throughout the cardiac cycle, which was suitable for the attachment of inflammatory features to the vessel wall. The fluid environment had focal properties. Combined with clinical studies, this study found that both sides of the carotid artery were indeed atherosclerosis-prone areas. Acute cerebrovascular diseases, such as stroke, are highly likely to happen when atheromatous plaque is dislodged in this area, as shown in Figure 8. The numerical simulation results in this paper agree well with this research [29]. The wall shear stress value of healthy blood vessels is not less than 0.5 Pa, and there is no growth environment for pathogenic features.  
As shown in Figure 9a, at t = 0.15 s, the heart was in the stage of contraction. The blood pressure in the coronary artery decreased gradually along the direction of blood flow from the aorta to the two branches. At this point, blood flow was in the initial stage of cardiac contraction, and the pressure difference between the inlet and outlet was small. As shown in Figure 9b, at t = 0.3 s, when cardiac contraction was completed, the wall pressure in the stagnation area at the bifurcation of the coronary artery was significantly higher than that in the nearby aorta and branch artery. A relatively obvious low pressure area appeared in the branch artery, which would enrich atherosclerotic particles in this area, and then affect vascular endothelial tissue lesions. The curved and bifurcated parts of the coronary artery with large curvature easily formed flow separation, and the fluid characteristics of low flow velocity and low shear stress formed the focal features of atherosclerosis.  
Figure 7: Shear stress variations in stenosis sites of healthy and lesioned vessels. (**a**) Shear stress extremes at the proximal end of healthy vessels. (**b**) Shear stress extremes at the proximal end of lesioned vessels. (**c**) Shear stress extremes at the stenosis site of the healthy vessels. (**d**) Shear stress extremes at the stenosis site of the lesioned vessels. (**e**) Shear stress extremes at the distal end of healthy vessels. (**f**) Shear stress extremes at the distal end of lesioned vessels.