主动脉瓣单叶置换在小儿生长中的瓣叶运动同步性和形状适应性研究

The Subarterial Ventricular Septal Defect is located under the right cusp of aortic valve, with the infundibular septum either partially or completely missing, without adequate support for the valves, producing a prolapse of the right coronary valve. The preferred treatment is resuspension of the leaflet free margin, central or commissural plication. If neo aortic valve still occurs moderate or severe regurgitation after repair, the Single Aortic Cusp Replacement can be considered. Clinical data has shown that it is mostly satisfactory after the Single Aortic Cusp Replacement. But for some children, neo aortic valves occur regurgitation again..The neo-aortic valve is composed of a bovine pericardial leaflet and two native leaflets after the Single Aortic Cusp Replacement. The applicant proposes that the difference of mechanical property between the three leaflets may be one reason causes regurgitation for neo aortic valve. In addition, aortic annulus and native leaflets become lager as child grows. The bovine pericardial leaflet fixed by Glutaraldehyde never grows up. As their growth, it may cause aortic valve regurgitation..This program proposes to regulate the mechanical property of the bovine pericardium by controlling glutaraldehyde concentration, fixing time and prestress value. The leaflet is designed by geometrical shape mimicked the venous valve. This program investigates the closure performance of neo aortic valve by modeling in vitro models and its pulsatile flow experiment, and by finite element models and its simulation experiment. The applicant proposes to validate the experiment results by Single Aortic Cusp Replacement for sheep with different weights to mimic the growth. Finally, the applicant proposes to create biomechanical models based on in vitro experimental results and the medical images to evaluate the possibility of clinical utility. This research hopefully improves the adaptive capacity of neo aortic valve as the child grows and the long term effect after the Single Aortic Cusp Replacement.

干下型室间隔缺损导致右冠瓣失去支撑，易发生脱垂。首选瓣叶成形手术治疗后，若仍有中重度反流，考虑主动脉瓣单叶置换。临床统计数据表明：单叶置换后有的效果满意，有部分小儿主动脉瓣出现反流。单叶置换手术中植入的牛心包瓣叶与两个自体瓣叶组成新主动脉瓣。申请人提出，两种瓣叶力学属性的差异，可能是引起新主动脉瓣关闭不全的原因。此外，手术后瓣环和自体瓣叶会长大，而经过戊二醛固定的牛心包瓣叶不会生长。随着时间推移，可能引起主动脉瓣关闭不全。.本项目拟控制戊二醛浓度、固定时间和预应力大小，调控牛心包力学属性。瓣叶采用静脉瓣几何形状设计。构建体外模型脉动流实验，力学模型数值模拟计算。评估新主动脉瓣的关闭性能。对不同体重（模拟生长）的绵羊单叶置换，验证实验结果。基于实验结果结合病例影像数据构建力学模型，探讨生物力学结果的实用性。本研究有望提高新主动脉瓣对小儿生长的适应能力，改善主动脉瓣单叶置换手术的中、远期疗效。

为了探究儿童主动脉瓣单叶置换(Single valve replacement, AVR)术后主动脉瓣关闭不全(Aortic valve insufficiency, AI)的生物力学机制并提出应对措施，利用三维造型设计软件构建理想化主动脉瓣模型及术后生长模型，分别构建了改变置换瓣叶游离缘长度、瓣叶高度以及改进设计的一种凹型结构；利用有限元分析方法，比较不同结构尺寸对术后主动脉瓣运动同步性和关闭性能的影响。数值模拟结果表明，置换瓣叶的闭合滞后于自体瓣叶，自体瓣叶贴合于置换瓣叶游离缘下方2 mm处。术后6年出现明显的AI。增加瓣叶高度不能改善术后效果且会增加瓣叶的最大应力。增加游离缘长度10%能够改善术后效果，当游离缘增大到15%，会造成主动脉瓣过长，导致主动脉瓣产生不良的贴合。凹型主动脉瓣较传统结构更有利于瓣叶对合，能够有效降低最大应力20%，效果最佳。研究结论是，儿童行AVR术后，会使瓣叶运动不同步，对合点发生偏移，术后6年出现AI现象。建议裁剪为增加游离缘长度10%的凹型结构，不建议增加瓣叶高度。