| Coronary atherosclerotic heart disease,which is also known as coronary disease,is caused by atherosclerotic lesions of coronary arteries that cause stenosis or obstruction of the blood vessel cavity,resulting in myocardial ischemia,hypoxia or necrosis.Coronary disease has become a major disease that endangers human health.Therefore,quickly and accurately diagnosing the degree of coronary artery stenosis is of great significance for the treatment plan of coronary heart disease.The fractional flow reserve(FFR for short)is the gold standard for evaluating the degree of coronary artery stenosis in functionalism,but clinical FFR measurement is invasive and has many limitations.FFR-CT is a non-invasive FFR calculation method.It calculates the FFR value by simulating the coronary blood flow state of the corresponding patient through computational fluid dynamics.Several groups of studies have demonstrated the feasibility of FFR-CT.However,few people have studied the flow distribution problem for multi-branch outlets in the coronary artery CFD simulation.There are two main situations in conducting coronary vascular CFD research,one is to simulate the FFR calculation when the blood vessel is in hyperemia,and the other is to simulate the real blood flow state in the blood vessel.In this paper,we propose two different kinds of branch outlet flow distribution methods for these two situations.In FFR calculation,the flow-pressure iterative method based on Murray's law is used to distribute the flow of each branch outlet of each coronary vessel.The numerical simulation calculation of the real coronary artery model by ANSYS CFX verifies the accuracy of this method.For the CT14 model,the pressure change value of the branch outlet has been less than 0.1% after 5th iterations,indicating that convergence was achieved,and the relative difference between the calculated FFR value and the clinically measured value is 0.5%.For the CHN13 model,after 30 iterations,the relative value of the pressure change of the branch outlets has been less than 0.1% except one branch outlet.It is considered that convergence has been achieved.and the relative difference between the calculated FFR value and the clinically measured value is 9.7%.The calculation results of the two models are obviously better than the method of directly allocating the flow rate according to the diameter of the branch outlet.For the analysis of the true blood flow state in coronary vessels,we allocate the flow according to the bifurcation level of the branch vessels in the entire coronary tree until the outlet of each branch.The calculation result is compared with the method of directly allocating the flow without considering the bifurcation level of the blood vessel through the CFD simulation of the real coronary vascular model.The two flow distribution methods exert very different flows on the outlet.There are two main reasons for this difference,one is that there is a narrowed part of the coronary vessels,and the other is that the diameter of each branch of the entire coronary tree does not obey Murray's law perfectly.In the hierarchical distribution,a smaller flow is applied at the place where the blood vessel narrows,which is more in line with the flow distribution in the blood vessel in the real state.According to the numerical simulation calculation,it can better explain the calculation result.That is,the narrowing of the blood vessel leads to a reduction in blood flow,the friction of the blood flow against the wall of the blood vessel is low,and the wall pressure value decreases very little along the direction of blood flow;The pressure value of the wall surface of the branch blood vessel without stenosis has a clear downward trend along the blood flow direction,the flow state is relatively chaotic at the location where bifurcations occur,and the value of blood flow rate and wall shear stress are greater than in other regions. |
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