Ventricle Valve Fluid-structure Interaction Finite Element Modeling And Its Application In Valve Replacement Surgery Design

As a common and frequently-occurring disease in patients,valvular heart disease is an important cause of increased morbidity and mortality of cardiovascular diseases.Currently,the major treatment of valvular heart disease is valve replacement surgery.Its surgical outcome is closely related to the implanted prosthetic valve.The choice of prosthetic valve in clinical practice is primarily dependent on the experiences and skill of the surgeon.Further study of prosthetic valve biomechanical behaviors may provide some preliminary theoretical support for valve selection and surgery outcome optimizations.Using computational mathematics methods to construct valve simulation models and perform virtual valve replacement surgery is an important method in current valve research.In this paper,a novel two-way three-dimensional fluid-structure interaction(FSI)valve model was proposed based on anisotropy valve mechanical properties and Arbitrary LagrangeEuler(ALE)method.This model was used to study the effects of valve size,material properties and valve thickness on the outcomes of replacement surgery.This provides a high efficiency and low risk approach for the selection of prosthetic valve and the optimization of surgical plan.The thesis included the following 4 parts:In this paper,the mechanical properties of pulmonary valve leaflets were obtained from biaxial testing and characterized by an anisotropic Modified Mooney-Rivlin model.The anisotropic Modified Mooney-Rivlin model was used to construct dynamic computational models of pulmonary root with normal tri-leaflet and bicuspid pulmonary valve(BPV)in patients with tetralogy of Fallot.Results from those models indicated that stress/strain distribution patterns on the leaflets were significantly different between the normal pulmonary valve and BPV models when the valve opened.In particular,when the valve was fully opened,the peak stress and strain values of BPV on the leaflets were 94.29% and 70.74% higher than normal pulmonary valve,respectively,and the geometric orifice area of BPV model was reduced 55.6 % from that of the normal pulmonary valve.Valve size is one of the important factors affecting the outcome of valve replacement surgery.Combining valve anisotropic material properties with blood flow data of the left ventricular outflow tract from a patient,a novel ALE-based two-way three-dimensional valve FSI model was introduced in this paper.This paper used FSI modeling method to construct aortic root models with 19 mm(No.19),21 mm(No.21),23 mm(No.23)and 25 mm(No.25)valve sizes,and performed virtual aortic valve replacement(AVR)with different valve sizes to optimize the selection of valve size in AVR surgery.Preliminary results suggested that using a larger valve size can significantly improve valve hemodynamic performance after AVR.The maximum flow velocity,mean systolic valve orifice pressure difference,mean systolic cross-valve pressure difference(SCVPD),and fluid shear stress(FSS)for Valve No.25 were 44.60%,49.08%,49.32% and 44.60% lower than that from Valve No.19,respectively.In addition,the geometric orifice area from Valve No.25 was 52.03% higher than that from Valve No.19.Prosthetic porcine and bovine valves are commonly used in AVR surgery,but the choice between the two valves has not been recommended clinically.This paper developed a more accurate twoway three-dimensional valve FSI model by using arterial pressure data from a patient as outlet boundary condition of model.Eight aortic root FSI models with 4 valve sizes and 2 valve materials(porcine valve and bovine valve)were constructed to investigate the effect valve materials on outcome of AVR surgery.Preliminary results showed that bovine valves had better hemodynamic performance and lower stress on the leaflets than that from porcine valves.The maximum flow velocity,mean SCVPD,peak SCVPD,leaflets FSS and stress from four bovine valve models were7.17%,8.92%,9.28%,6.61% and 5.76% lower than that from porcine valve models,respectively.The bovine model had a larger geometric orifice area,which is 9.56% higher than the porcine model.Based on the material properties,boundary conditions and modeling methods of the above porcine valve models,FSI models of thin porcine valves with a thickness of 0.24 mm and 4 valve sizes were developed.The effects of leaflet thickness on the valve hemodynamics and the stress on the leaflets were studied by comparing results from thin and thick porcine valve model.Preliminary results showed that the leaflets thickness significantly affected valve stress distribution.However,their effect on valve hemodynamics was minor.Compared with the porcine thick-valve models,the thickness of the thin porcine valve model was reduced by 40%,but the mean stress on the leaflet was increased by 46.52%.Innovations of this paper included: a)Based on anisotropy valve material properties and ALE method,a novel two-way three-dimensional valve FSI model was introduced and used to perform virtual valve replacement surgery.This approach provided the possibility to use computational models to accurately simulate valve mechanical conditions and optimize valve replacement surgery design and procedures;b)Combining dynamic finite element model with pulmonary valve anisotropic material properties to investigate the effect of BPV geometric structure on valve structure stress/strain distributions;c)Using FSI model and blood flow data from a patients,virtual AVR surgeries with different valve sizes were simulated to study the impact of valve size on AVR surgery.A preliminary valve size optimization plan was suggested;d)Using arterial pressure data from a patient,FSI models of porcine and bovine valves with their respective material properties were developed to guide porcine and bovine valve selection in AVR surgery;e)FSI valve models were used to perform virtual surgery with different valve thickness to study effect of valve thickness on AVR surgical outcome.