| Instantaneous wave free ratio(i FR)is a standard for evaluating cardiovascular hemodynamic changes and myocardial ischemia caused by coronary stenosis in resting state.It is defined as the ratio of the distal pressure(Pd)and the proximal pressure(Pa)of stenosis in the wave free period(WFP)at rest.Multi center large clinical studies show that i FR has good consistency with the "gold standard"(FFR)for evaluating myocardial ischemia.However,the invasive measurement of i FR requires that the pressure guide wire be placed in the coronary artery,which limits the clinical application and development of this technology.At present,the numerical simulation technology based on computational fluid dynamics can be used for noninvasive calculation of coronary artery hemodynamics.The numerical simulation technology of FFR is relatively mature,but the research on numerical simulation of i FR is less.In existing research on i FRCT numerical simulation,the simulation of Pa and the calculation of microcirculation resistance in WFP are not accurate enough,resulting in insufficient accuracy of i FRCT.The details are as follows: First of all,the accurate simulation model of i FRCT was not built,and the influencing factors were not analyzed to clarify the physiological parameters that should be considered in the model;Secondly,the accurate and patient specific heart model was not established to simulate the pressure waveform of Pa at rest;Thirdly,the calculation of coronary microcirculation resistance is based on two coronary blood flow distribution assumptions,and the coefficient is assumed to be constant,which cannot reflect the personalized microcirculation;Finally,The simulated Pa and Pd waveforms often lack the verification of clinical results.In the past,the determination method of WFP depends on ECG,and data simulation needs to determine the range of WFP for independent pressure waveform.In this thesis,based on the influencing factors of myocardial ischemia,the 0D/3D closed-loop geometric multi-scale model of i FRCT was constructed.An accurate and personalized heart model and microcirculation resistance model have been developed.The specific research contents are as follows:1.Construction of 0D/3D closed-loop geometric multi-scale model of i FRCT.The i FRCT numerical calculation needs to prove the cardiac resting state,accurate Pa,Pd waveform and WFP range.A personalized 3D model based on patients’ CTA images was constructed,which comprehensively considered the influence of coronary artery geometry;The 3D model entrance is an accurate and personalized 0D heart model simulating the Pa waveform in the resting state;3D model outlet is 0D microcirculation resistance model providing accurate and personalized outlet boundary conditions;Coronary hemodynamics simulation is realized through 2D/3D geometric multi-scale coupling.In the simulation results,the pressure waveforms of proximal and distal stenosis are extracted and compared with the clinical waveforms to verify the accuracy of the simulation results.WFP is determined based on clinical pressure waveform,and i FRCT is calculated and evaluated.2.Research on Study on the influencing factors of myocardial ischemia in resting state.The comprehensive analysis of influencing factors provides theoretical support for the construction of simulation model and the assignment of boundary conditions.Statistics of 207 patients’ physiological parameters,pathological parameters,cardiac output related parameters and blood pressure related parameters showed that systolic blood pressure,diastolic blood pressure and cardiac output as the input conditions of the heart were more personalized and accurate than other conditions.The study on the relationship between microcirculation resistance(Rm)and myocardial ischemia in 90 patients in different stenosis degrees showed that Rm had a significant effect on myocardial ischemia.As the outlet boundary condition of the simulation model,it can not only conform to physiology,but also improve the accuracy of the model.3.Research on constructing accurate and personalized heart model.The accurate simulation of Pa waveform in resting state is the basis of accurate simulation of i FRCT.According to the anatomical structure of the heart,a lumped parameter model of the blood circulation system was constructed.With the pressure volume curve as the constraint condition,the heart rate,blood pressure and cardiac output of 30 patients were taken as the personalized parameter input,and the simulated annealing algorithm was improved to optimize the aortic pressure waveform(U0)and cardiac output(I0).The results showed that the clinical waveforms of U0 and I0 were in good agreement with the optimized waveforms,and the mean root mean square error of waveform data was 2.26% ± 1.11%.The personalized heart model can accurately and rapidly simulate U0 and I0,providing accurate entrance boundary conditions for0D/3D geometric multi-scale simulation.4.Research on constructing personalized microcirculation resistance model.The previous calculation of Rm was based on a large number of clinical statistics and assumptions,which could not reflect the individuation of patients.To solve the problem of left-right coronary shunts,the cross-sectional areas of left-right coronary arteries of 30 patients were counted.With the goal of the flow ratio of left-right coronary arteries being 6:4,the flow of left-right coronary arteries was obtained by fitting,which was proportional to the 3/4 power of the cross-sectional area.To clarify the shunting principle of bifurcation vessels,Rm was calculated when the power of the blood flow diameter scaling law was 3,2.7 and 7/3,respectively.This was used as the outlet boundary condition of the 0D/3D geometric multi-scale model for numerical simulation of 26 patients.The results show that when the power was 7/3,FFRCT and FFR have the highest correlation,consistency and accuracy.5.Research on i FRCT validation and evaluation.The verification and evaluation of i FRCT results is an effective means to verify the accuracy of 0D/3D closed-loop geometric multi-scale.By comparing the coincidence degree and root mean square error of 103 clinical and simulated pressure waveforms(Pa and Pd),the results show that the simulation model can accurately simulate the pressure waveform of proximal and distal stenosis in the resting state.109 cases of clinical pressure waveform were extracted,and cardiac cycle,diastolic period and signal delay time were counted by curve slope method.It was proposed that the range of WFP based on pressure waveform was 25% of diastolic period to 8% of diastolic period before the end of cardiac cycle.At this time,the accuracy of i FR was 84.47%.Based on the above research,the i FRCT values of 103 patients were calculate,with high correlation and consistency with i FR.The accuracy of i FRCT was 93.25% and 99.03% when i FR was0.86 and 0.93 as classification variables.In summary,this study clarified the influencing factors of myocardial ischemia and the principle of coronary shunting,and built an accurate and personalized heart model and coronary microcirculation resistance model to achieve 0D/3D geometric multi-scale simulation of i FRCT.The comparison between the simulation and the clinical pressure waveform verifies that the simulation state is a resting state,and the results of Pd and Pa are accurate.The 0D/3D geometric multi-scale numerical calculation of i FRCT provides theoretical and technical support for evaluating myocardial ischemia,and has positive significance for noninvasive evaluation of myocardial ischemia at rest. |
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