Seaman Clara, Akingba A George, Sucosky Philippe
J Biomech Eng. 2014 Apr;136(4). doi: 10.1115/1.4026575.
The bicuspid aortic valve (BAV), which forms with two leaflets instead of three as in the normal tricuspid aortic valve (TAV), is associated with a spectrum of secondary valvulopathies and aortopathies potentially triggered by hemodynamic abnormalities. While studies have demonstrated an intrinsic degree of stenosis and the existence of a skewed orifice jet in the BAV, the impact of those abnormalities on BAV hemodynamic performance and energy loss has not been examined. This steady-flow study presents the comparative in vitro assessment of the flow field and energy loss in a TAV and type-I BAV under normal and simulated calcified states. Particle-image velocimetry (PIV) measurements were performed to quantify velocity, vorticity, viscous, and Reynolds shear stress fields in normal and simulated calcified porcine TAV and BAV models at six flow rates spanning the systolic phase. The BAV model was created by suturing the two coronary leaflets of a porcine TAV. Calcification was simulated via deposition of glue beads in the base of the leaflets. Valvular performance was characterized in terms of geometric orifice area (GOA), pressure drop, effective orifice area (EOA), energy loss (EL), and energy loss index (ELI). The BAV generated an elliptical orifice and a jet skewed toward the noncoronary leaflet. In contrast, the TAV featured a circular orifice and a jet aligned along the valve long axis. While the BAV exhibited an intrinsic degree of stenosis (18% increase in maximum jet velocity and 7% decrease in EOA relative to the TAV at the maximum flow rate), it generated only a 3% increase in EL and its average ELI (2.10 cm2/m2) remained above the clinical threshold characterizing severe aortic stenosis. The presence of simulated calcific lesions normalized the alignment of the BAV jet and resulted in the loss of jet axisymmetry in the TAV. It also amplified the degree of stenosis in the TAV and BAV, as indicated by the 342% and 404% increase in EL, 70% and 51% reduction in ELI and 48% and 51% decrease in EOA, respectively, relative to the nontreated valve models at the maximum flow rate. This study indicates the ability of the BAV to function as a TAV despite its intrinsic degree of stenosis and suggests the weak dependence of pressure drop on orifice area in calcified valves.
二叶式主动脉瓣（BAV）由两片瓣膜构成，而非正常三叶式主动脉瓣（TAV）的三片瓣膜，它与一系列可能由血流动力学异常引发的继发性瓣膜病变和主动脉病变相关。虽然研究已经证实BAV存在一定程度的狭窄以及偏心口射流的存在，但这些异常对BAV血流动力学性能和能量损失的影响尚未得到研究。这项稳流研究对正常状态和模拟钙化状态下的TAV和I型BAV的流场和能量损失进行了体外比较评估。采用粒子图像测速技术（PIV）测量，以量化正常和模拟钙化的猪TAV和BAV模型在跨越收缩期的六种流速下的速度、涡度、粘性和雷诺剪切应力场。BAV模型通过缝合猪TAV的两个冠状动脉瓣叶创建。通过在瓣叶基部沉积胶珠模拟钙化。瓣膜性能通过几何口面积（GOA）、压降、有效口面积（EOA）、能量损失（EL）和能量损失指数（ELI）来表征。BAV产生一个椭圆形口和一个偏向无冠状动脉瓣叶的射流。相比之下，TAV具有圆形口和沿瓣膜长轴排列的射流。虽然BAV存在一定程度的狭窄（在最大流速下，相对于TAV，最大射流速度增加18%，EOA降低7%），但其EL仅增加3%，其平均ELI（2.10 cm²/m²）仍高于表征严重主动脉瓣狭窄的临床阈值。模拟钙化病变的存在使BAV射流的排列正常化，并导致TAV射流轴对称性丧失。它还放大了TAV和BAV的狭窄程度，在最大流速下，相对于未处理的瓣膜模型，EL分别增加342%和404%，ELI分别降低70%和51%，EOA分别降低48%和51%。这项研究表明，尽管BAV存在内在狭窄程度，但它仍能发挥TAV的功能，并表明钙化瓣膜中压降对口面积的依赖性较弱。
