| Arterial switch operation is an effective surgical procedure for the treatment of complete transposition of the great arteries.However,new aortic insufficiency is a common failure mode of the arterial switch operation and the patient’s death cause after operation.According to the CTA image of the patient suffered from new aortic insufficiency after the completion of arterial switch operation,it can be observed that there is difference between the patient and healthy person in terms of opening direction of the valve leaflet and the ventricular flow cavity shape.This Paper studies the scientific problem of opening direction of the valve leaflet and the ventricular flow cavity shape to the curative effect mechanism of arterial switch operation from the perspective of biomechanics in accordance with finite element analysis method and in-vitro model verification test.Based on research of simulation method of time-phased fluid-structure interaction,the influence on calculation results of element type and boundary condition was compared and studied,which has determined a kind of relatively reasonable finite element model of aortic root.Then,the influence biomechanical mechanism of arterial switch operation treatment by the opening direction of the valve leaflet and the ventricular flow cavity shape was calculated by the above-mentioned finite element model.In the end,an in-vitro model was made to verify the test.The research of this topic will help clinicians to make more convenient and efficient,scientific and reasonable treatment plan for aortic transfer operation,providing theoretical direction for improving the treatment plan of complete transposition of the great arteries.Concrete research content includes following several aspects: first of all,the classification and treatment of aortic valve regurgitation,simulation and in vitro modeling of aortic root,biomechanical mechanism are presented as background.Secondly,six geometric modeling method,tissue properties,numerical analysis method,evaluation parameters of mechanical behaviors for aortic root,and experimental method in vitro are presented as the theory basis researching biomechanics mechanism of aortic root.And then,the numerical simulation of the structural finite element model is mainly composed of two parts that the effects of the shell element and the fiber organization element model on the calculation results are compared,and the change in valve leaflet shape of aortic root to complete whole cardiac cycle,flow field time and spatial distribution of aortic root,and leaflet coaptation are calculated by the numerical simulation of time-phased fluid-structure interaction.The change of angle between valve leaflet opening and the central axis of the aorta,and the influence on arterial switch operation treatment by changing the shape of ventricular flow cavity are studied.An in-vitro model and appendage of the aorta root is made to calibrate the compliance and resistance of the aorta and coronary arteries in an in-vitro experimental environment.The physiological pulsating flow field is provided by Vivitro heart-vessel experimental device.The electromagnetic flowmeter is used to measure the parameters such as forward flow and counter flow and transmembrane pressure.The conclusion and prospect of this paper discuss the limitations of this study.Solutions are provided for new problems in research process.There are some significant results as follows.First of all,a reasonable finite element model was established.From the modeling point of view,the complex element is more complex than the shell element model in creating geometric models,dividing grids and solving settings.From the number of units,calculation iteration steps and solution time,the computation amount of the two models is close,and the maximum stress position and maximum stress value of valve leaflet are also close.The calculation results of the valve leaflet on resultant force showed a great difference when using two kinds of element types to calculate the aortic valve closure.Secondly the effect of the opening direction of the valve leaflet on the valve closure function was studied by numerical simulation.After observation of healthy people and 2 cases of arterial switch operation,there was case model of the aortic root with aortic insufficiency.The steady flow calculation was completed by constructing the flow field model respectively.From the point of view of flow resistance,compared with normal aortic valve,the difference of opening direction of valve after the operation will increase local resistance of the blood stream,thus increasing energy loss.From the reverse pressure gradient theory of aortic valve closure,the change in the direction of the valve opening will cause the difference in the pressure difference of the valve leaflet.Finally The influence on aortic valve closure function of opening direction of different valve leaflets and shape of ventricular flow cavity was verified by in-vitro experiment.The measured value of transvalvular pressure gradient and backflow percentage of opening direction of different valve leaflets and model of ventricular flow cavity all meet the domestic standards.The measured area of the effective opening accords with the size of the valve opening.There are differences in the transvalvular pressure gradient of bioprosthetic valve,backflow percentage and effective opening area under different cardiac output and between different models of different valve angle,of which the opening direction of the valve leaflet is associated with the backflow percentage.The above quantitative theoretical analysis results can be used as the theoretical basis for geometrical configuration of aortic root before the operation.This will help clinicians to determine the geometric configuration of new aortic root,and provide scientific reference and reasonable advice for the formulation of the surgical procedures.It can also provide more detailed pathological information for patients,and it has positive significance to avoid medical disputes. |
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