| Coronary Fractional Flow Reserve(FFR)is currently the gold standard for evaluating functional myocardial ischemia.In recent years,the newly developed Instantaneous wave-Free Ratio(IFR)evaluation index has shown a good correlation with FFR.However,FFR and IFR are both invasive detection techniques,and their clinical applications are both limited.The establishment of a non-invasive myocardial ischemia evaluation method to guide the treatment of coronary stenosis is a difficult problem to be solved.In this study,based on the patient's coronary CTA images and the patient's indicidualized lumped parameters model,a hemodynamic geometric multiscale model of coronary 0D-3D coupled model was constructed.Computational fluid dynamics(CFD)was used to calculate the flow rate and pressure of coronary system.This models can non-invasive estimate the IFRct in the wave free period at rest condition and FFRct(or FFRss)at hyperemia state;establish non-invasive functional evaluation of myocardial ischemia caused by coronary stenosis;provide an effective diagnostic and evaluation tool for clinical myocardial ischemia caused by coronary stenosis.The research content of this dissertation includes the following three parts:(1)Study on Open-loop hemodynamic geometric multiscale model for FFR:This study developed an open-loop hemodynamic geometric multiscale model of coronary 0D/3D coupled method,based on patient's coronary CTA images and personalized lumped parameter model.The flow rate and pressure of coronary arteries were calculated.This model can calculate FFRct and IFRct of coronary system at the rest state and hyperemia to non–invasively evaluate myocardial ischemia.In this model,the 3D model of coronary system based on CTA images can describe coronary tree structure and reflect the location and stenosis rate of of coronary arteries,while the physiologic lumped parameter model can provide the physiologically realistic boundary conditions of hemodynamic simulation for patient's 3D model.It includes the outlet boundary conditions which represent coronary microcirculation and systemic circulation,while the inlet boundary condition which represents the cardiac output and pressure of heart function.The simulation results show that: by using the relationship between the structure and function of coronary system,which called scaling law,the model can obtain more accurate the coronary afterload;By optimizing the parameters of lumped parameter model,the individualized physiological lumped parameter model of coronary system module and heart module can be obtained.It can ensure the accuracy of FFRct and IFRct calculation.At the same time,this study explored the effect of stenosis rate coronary artery(40%-90%)on IFRct: with the increase of stenosis rate on LAD,the LAD flow rate and IFRct both decreased.When IFRct is in the "grey area" of 0.86-0.93,stenosis rate of LAD is in the range of 55%-65%,and clinical FFR is required to guide further treatment.(2)Study on Closed-loop hemodynamic geometric multiscale model for FFR:This study described a closed-loop hemodynamic geometric multiscale model of coronary 0D/3D coupled method based on coronary CTA images of patient and personalized lumped parameter model.The flow rate and pressure of coronary arteries were calculated.This model can calculate FFRct and IFRct of coronary system at the rest state and hyperemia to non–invasively evaluate myocardial ischemia.Compared with the open-loop hemodynamic geometric multiscale model,in this model,the end of coronary microcirculation are fed back to the heart module,which can realistically simulate the mutual adjustment relationship between coronary system and heart.The simulation results show that: the improved closed-loop hemodynamic geometric multiscale model can make sure the calculation results of FFRct and IFRct more acuurate.And the simulation results of them are consistent with each other.(3)Study on fast hemodynamic geometric multiscale model for FFRss:This study provided a fast hemodynamic geometric multiscale model of coronary 0D/3D coupled method to non-invasive obtain the FFRss based on coronary CTA images of patient,combined with the inlet pressure and outlet resistance boundary conditions.By using steady-state method,the flow rate and pressure of coronary arteries were numerically calculated.In addition,the study also performed the sensitivity analysis of aortic inlet pressure(Pa)and left ventricular myocardial mass(MASSlv)on FFRss and CFRss,respectively.The calculation results show that: this fast geometric multiscale method can shorten the time cost of computational solution from several hours to 20 minutes,which reaching the expected goal of clinical application.In summary,this paper used three different hemodynamic geometric multiscale models,namely open-loop geometric multiscale model,closed-loop geometric multiscale model and steady-state fast geometric multiscale model,to systematically perform the non-invasive calculation of myocardial ischemia caused by coronary artery stenosis.The main contents of this study included the coronary lumped parameter model and the numerical simulation of open-loop geometric multiscale model,closedloop geometric multiscale model and steady-state fast calculation model of resistance boundary conditions.These three different studies provided a basic method for assessing whether coronary stenosis would cause myocardial ischemia and functional assessment of coronary stenosis.It provided a hemodynamic perspective for clinically coronary artery disease.While providing guidance and advice for doctors to diagnose and treatment strategies,the academic point of view has a certain clinical medical application value. |
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