Bruecker Ch, Li Qianhui
School of Mathematics, Computer Science and Engineering, City, University of London, Northampton Square, London EC1V 0HB, UK.
Bioengineering (Basel). 2020 Dec 8;7(4):158. doi: 10.3390/bioengineering7040158.
Background-Physiological helical flow in the ascending aorta has been well documented in the last two decades, accompanied by discussions on possible physiological benefits of such axial swirl. Recent 4D-MRI studies on healthy volunteers have found indications of early generation of helical flow, early in the systole and close to the valve plane. Objectives-Firstly, the aim of the study is to investigate the hypothesis of premature swirl existence in the ventricular outflow tract leading to helical flow in the valve plane, and second to investigate the possible impact of two different mechanical valve designs on the preservation of this early helical flow and its subsequent hemodynamic consequences. Methods-We use a pulse duplicator with an aortic arch and High-Speed Particle Image Velocimetry to document the flow evolution in the systolic cycle. The pulse-duplicator is modified with a swirl-generating insert to generate early helical flow in the valve plane. Special focus is paid to the interaction of such helical flow with different designs of mechanical prosthetic heart valves, comparing a classical bileaflet mechanical heart valve, the St. Jude Medical Regent valve (SJM Regent BMHV), with the Triflo trileaflet mechanical heart valve T2B version (Triflo TMHV). Results-When the swirl-generator is inserted, a vortex is generated in the core flow, demonstrating early helical flow in the valve plane, similar to the observations reported in the recent 4D-MRI study taken for comparison. For the Triflo trileaflet valve, the early helical flow is not obstructed in the central orifice, similar as in the case of the natural valve. Conservation of angular momentum leads to radial expansion of the core flow and flattening of the axial flow profile downstream in the arch. Furthermore, the early helical flow helps to overcome separation at the outer and inner curvature. In contrast, the two parallel leaflets for the bileaflet valve impose a flow straightener effect, annihilating the angular momentum, which has a negative impact on kinetic energy of the flow. Conclusion-The results imply better hemodynamics for the Triflo trileaflet valve based on hydrodynamic arguments under the discussed hypothesis. In addition, it makes the Triflo valve a better candidate for valve replacements in patients with a pathological generation of nonaxial velocity in the ventricle outflow tract.
背景——在过去二十年中，升主动脉内的生理性螺旋血流已得到充分记录，同时也伴随着关于这种轴向漩涡可能带来的生理益处的讨论。最近对健康志愿者进行的4D-MRI研究发现，在收缩早期且靠近瓣膜平面处存在螺旋血流早期形成的迹象。目的——首先，本研究的目的是调查心室流出道中过早出现漩涡导致瓣膜平面出现螺旋血流这一假说，其次是研究两种不同机械瓣膜设计对这种早期螺旋血流的保留及其后续血流动力学后果的可能影响。方法——我们使用带有主动脉弓的脉搏复制器和高速粒子图像测速技术来记录收缩期循环中的血流演变。通过在脉搏复制器中插入产生漩涡的装置来在瓣膜平面产生早期螺旋血流。特别关注这种螺旋血流与不同设计的机械人工心脏瓣膜之间的相互作用，将经典的双叶机械心脏瓣膜圣犹达医疗Regent瓣膜（SJM Regent BMHV）与Triflo三叶机械心脏瓣膜T2B版本（Triflo TMHV）进行比较。结果——当插入漩涡发生器时，在核心流中会产生一个漩涡，表明在瓣膜平面存在早期螺旋血流，这与为进行比较而开展的近期4D-MRI研究所报告的观察结果相似。对于Triflo三叶瓣膜，早期螺旋血流在中心孔处不会受到阻碍，这与天然瓣膜的情况类似。角动量守恒导致核心流在下游呈径向扩张，且轴向流型在主动脉弓处变平。此外，早期螺旋血流有助于克服外曲率和内曲率处的分离。相比之下，双叶瓣膜的两个平行瓣叶会产生整流作用，消除角动量，这对血流的动能有负面影响。结论——基于所讨论的假说，从流体动力学角度来看，结果表明Triflo三叶瓣膜具有更好的血流动力学性能。此外，这使得Triflo瓣膜成为心室流出道出现非轴向速度病理性产生的患者进行瓣膜置换的更佳选择。
