Research On Hemodynamics Of Multicomponent-Multiphase In Narrow Vessel

Cardiovascular and cerebrovascular diseases have become the main killer to human health,of which 75% of cases are caused by atherosclerotic plaques,and its prevalence rate is still rising.The calculation and analysis of hemodynamics based on computational fluid dynamics has become an important method to study the mechanism of atherosclerotic plaque formation,the evaluation of atherosclerotic plaque risk,the planning of treatment plan and the evaluation of medical device design.At present,the two-phase flow model and non-Newtonian fluid model have been widely used in the analysis of hemodynamics,but these two models cannot simultaneously calculate the distribution of a variety of blood components in the blood vessels,resulting in the inability to quantitatively analyze the relationship between the concentration of low density lipoprotein(the direct cause of atherosclerotic plaque growth)and the growth of atherosclerotic plaques.In this paper,multicomponent flow model and multiphase flow model are coupled to form a multicomponent-multiphase flow model,and applied to the hemodynamic calculation and analysis.It can calculate the concentration of red blood cells,high density lipoprotein(HDL),low density lipoprotein(LDL)and other blood components at the same time,to achieve quantitative analysis of low-density lipoprotein and further understand the growth mechanism of plaques.In this paper,the main results and innovations are as follows:1.The differences of results between the multicomponent-multiphase model and the Newtonian fluid,the non-Newtonian fluid and the two-phase flow model were analyzed in a narrow vessel.The multicomponent-multiphase model can not only calculate the hemodynamic characteristics and the erythrocyte distribution results similar to the non-Newtonian fluid and the two-phase flow model,but also can get HDL and LDL concentration distribution results.Comparing with other models,it is proved that the multicomponent-multiphase model is suitable for hemodynamic calculation.2.The effects of blood flow velocity,hematocrit and LDL diffusion coefficient on blood flow characteristics were analyzed in a narrow vessel based on a multicomponent-multiphase model.And found that changes in blood flow velocity will lead to changes in hemodynamic parameters and changes in blood components concentration.And the greater the speed of blood flow,the more easily to be rupture of the plaque.Therefore,pulsating velocity will makes the constantly changes of hemodynamic parameters.Increased hematocrit can cause near-wall velocity to decrease,cause wall shear stress and the pressure gradient to increase.So it can be seen that the plaque of patient with high hematocrit is more likely to rupture.The increase in LDL diffusion coefficient only changes the LDL concentration value,which leads to more LDL infiltration into the vessel wall.3.The effect of plaque geometric parameters on blood flow characteristics was analyzed based on the multicomponent-multiphase flow model.It is found that the increase in plaque height leads to the increase in backflow,and the shear stress and pressure gradient increase which result in the higher risk of plaque rupture.And also leads to the increase in the burden of blood vessels and cardiac.With the increase of plaque height,the concentration of LDL at the flow separation position increased first and then decreased,so the growth rate of plaques increased first and then decreased.The greater the plaque width is,the smaller the shear stress and pressure gradient on the surface of the plaque will be that the risk of plaque rupture also be lower;and the lower the LDL concentration will be so that the rate of plaque growth will be smaller.Compared with the symmetric plaque,the more complicated blood flow appears in the downstream of the asymmetric plaque,and the greater wall shear stress and pressure gradient appear at the surface of the plaque,it means that the higher probability of the plaque rupture.At the same time,the concentration of LDL will be greater and means that the plaque will grow faster.4.Based on the multicomponent-multiphase flow model,the distribution of blood flow in reconstructed carotid artery was analyzed.It was found that low flow velocity and wall shear stress was found on the medial side of the curved blood vessel which caused the high LDL concentration in this region where would lead to plaque formation.At the left and right carotid bifurcation sites,the presence of plaques was found on the outsides of the internal carotid artery where forms the low velocity and wall shear stress accompanied by reflux and spiral flow resulting in high HDL,LDL concentration and low erythrocyte concentration in this region.It is easy to cause vascular wall endothelial cell hypoxia resulting in vascular wall permeability increased,more LDL will penetrate into the blood vessel wall,and the plaque will grow further.5.By comparing the blood flow characteristics of left and right carotid arteries of a patient,it was found that the right carotid artery plaque had seriously affected the patient's health.Not only the blood flow is more complex in plaque downstream,but also the right internal carotid artery blood supply decreased resulting in the right side of the brain blood vessels insufficiency.And also lead to the pressure of other blood vessels and heart increases that makes the blood vessels and heart bear a greater burden.And in the right carotid,a very high wall pressure gradient and shear stress appear at the plaque surface where in the high risk of plaque rupture.The patient should be treated in a timely manner to prevent sudden brain disease.The formation of intractable intravascular atherosclerotic plaques is related not only to hemodynamic parameters,but also to the abnormalities of Abnormal LDL concentration which is a direct predisposing factor for the growth of atherosclerotic plaques.Multicomponent-multiphase flow model can simultaneously calculate the hemodynamic parameters and the results of a variety of blood component concentrations.It can help to study on the formation mechanism of the plaque from the mechanical effects and material induction.And also can help to evaluate the patient's condition effectively.This study has enriched the research methods of pathogenesis of arterial disease which can promote clinical research related with atherosclerotic plaques.