Study Of The Hemodynamic Mechanisms And Lipid Transport Characteristics Of Atherosclerosis

Atherosclerosis is a common vascular disease and is the main cause of coronary heart disease,cerebral infarction and peripheral vascular disease.Hemodynamic parameters such as wall shear stress,blood pressure and eddy generation play essential roles in the formation and development of atherosclerosis.As such,assessing the mechanisms of atherosclerotic lesion formation from a hemodynamics perspective is critical for the prevention,diagnosis and treatment of cardiovascular diseases.Using a combination of a patient-data analysis and numerical simulations,the formation,mechanistic development,and resulting pathological effects of atherosclerosis were assessed.Medical images were used to generate three-dimensional vascular models which are susceptible to atherosclerotic lesions.Fluid-solid two-way coupling technology was utilized and pulsating blood flow was set as a boundary condition.The model was used to systematically characterize flow and lipid mass transport in the blood,providing a reference for the prevention and medical treatment of atherosclerosis.The main work carried out is as follows:(1)The cardiac hemodynamic parameters of both atherosclerotic and healthy individuals were collected and analyzed by impedance cardiography to assess the effect of changes in blood physiological parameters on atherosclerosis.The results indicated that in terms of cardiac pump function,blood pressure of the pathological group was generally higher,and cardiac output was lower.When assessing system load the vascular compliance of the pathological group was lower and the total peripheral resistance was significantly higher.Further,the difference between the pathological and healthy groups increased with age,and there were certain differences between genders.Hypertension,low cardiac output,and high peripheral resistance are important factors that promote the formation of atherosclerosis.(2)The effects of vessel wall elasticity and blood non-Newtonian fluid properties on blood flow were analyzed.The results showed that an elastic vessel wall can store blood via dilation during cardiac systole and reduce both blood flow resistance and wall shear stress.Additionally,the non-Newtonian fluid characteristics of blood can reduce the impact of blood flow pulsation on wall stress and makes the overall distribution of system stress more uniform and stable.Therefore,neither of them can be ignored in hemodynamics.In all of the simplified models examined,the rigid wall model had the largest error and was the least reliable.(3)Hemodynamics was used to measure the effects of changes in physiological parameters on atherosclerosis and define the underlying mechanisms.The results showed that in the range of normal physiological values,blood flow had the greatest impact on wall shear stress while blood pressure had minimal effects.In vivo,the different physiological parameters synergize and the resulting compounded effects on blood flow are consistent with the change in incidences of atherosclerosis as described in the medical literature.This suggests that blood flow plays a leading role in the formation of atherosclerosis among all physiological factors.(4)The distribution of lipid concentration in curved and bifurcated vessels was studied to analyze its effect on atherosclerosis.The results showed that lipid concentration near the vessel wall was significantly higher than the average concentration in the mainstream due to wall permeation.The distribution was regular and regions of high concentration were often located in areas with low wall shear stress.However,low wall shear stress areas did not always have high lipid concentrations.In the mainstream,the flow field has an important influence on the distribution of lipid concentrations.Lipids were found in high concentrations in a ring near the wall of curved and bifurcated blood vessels,which are conducive to the accumulation of lipids on the wall.(5)The effect of vascular bending on the formation of atherosclerosis was also assessed.The results showed that as vascular curvature increased,shear stress on the inner surface of the curvature decreased,and both the intensity of secondary flow and the concentration of lipids increased.This indicated that the occurrence of atherosclerosis was increased by vascular bending.Further,a positive correlation was noted between the intensity of secondary flow and lipid concentration on the wall.The increase in secondary flow in the curved area is the predominant reason for the increase in lipid concentration.When the bend angle was small,the lipid concentration at the inner wall of the bending part increased as flow rate increased;however,when bend angle was larger,the lipid concentration decreased.(6)To examine the mechanisms of atherosclerotic development,blood flow field and lipid concentration distribution were assessed.The results showed that as plaques grow,the velocity around the stenosis and wall shear stress increases sharply,which can cause endothelial cell damage.In the early stages of lesion development,the increase in lipid concentration is the primary cause of continuous plaque development,and the damage of endothelial cells in the later stage will further promote the development of plaque.The plaque reduces the shear stress and increases lipid concentration in the downstream area,which could cause the expansion of the lesion.A decrease in the elasticity of the blood vessel wall further enhances the plaques effect on the flow field,indicating that a loss of wall elasticity also contributes to atherosclerosis.