Dynamic modelling of a stented aortic valve

[摘要] Aortic valve replacements are frequently performed during heart surgery. However,since this is quite a stressful procedure, many patients are turned down formedical reasons. Stented valves, designed and manufactured for percutaneousinsertion, eliminate many of the risks involved in open-heart surgery, thus providinga solution to patients not deemed strong enough for open-chest aorticvalve replacements. The aortic valve is a complex structure, and therefore numericalsimulation is necessary to obtain flow and stress data to support thedesign of a prosthetic heart valve in the absence of viable physical measuringmethods.To aid in the design of a prosthetic heart valve, various finite element valvemodels were created, and the fluid structure interaction (FSI) between thevalves and the blood was simulated using commercial finite element software.The effect of the geometry of the leaflets on the haemodynamic behaviour overthe cardiac cycle was investigated. It was found that leaflet dimensions shouldbe chosen judiciously, because of their considerable effect on the stress distributionand performance of the valve. A simple leaflet geometry optimisationwas done for a 20 mm and 26 mm valve, respectively, by means of existinggeometry relationships found in the literature. Simulations were done to obtain the maximum leaflet attachment forcesthat can be used by a stent designer for fatigue loading, or to investigate thestructural strength of the stent. These simulations were numerically validated.The effect of leaflet thickness and stiffness on resistance to opening, stressdistribution and strain were investigated. Results showed that leaflet thicknesshas a greater effect on the performance of the valve than leaflet stiffness, andthereby validated the results of similar tests contained in the literature. Aftersimulating over-, as well as under-dilation of a stented valve, it was found thatproblems associated with over-dilation can be minimised to a certain extentby increasing the coaptation1 region of the leaflets.A simple pulse duplicator was designed based on a four-element Windkesselmodel. The pulse duplicator was used to study the performance of the prototypevalves by means of high-speed photography, the results of which werefed into one of the numerical finite element models and compared to real valveperformance. Some of the prototype valves showed efficiencies of 88%.

[发布机构] Stellenbosch University