Transcatheter aortic valve implantation (TAVI) has become the alternative procedure to high-risk patients who are diagnosed with aortic valve stenosis. Differently from the traditional open-chest surgical procedure, a small variation on the prosthetic aortic valve deployment angle is expected with the TAVI procedure. The hemodynamic patterns of the blood flow in the ascending aorta are related to the development of many cardiovascular diseases. There are, however, few data available in the literature correlating the aortic valve tilt angle to hemodynamic effects. In this work, a 3D printed aorta model made of a transparent silicon resin was produced, based on the anatomy of a specific patient submitted to a TAVI procedure. The stereoscopic Particle Image Velocimetry technique was employed to measure three-component velocity fields at closely spaced cross-sectional planes, along the ascending aorta. The measurements were performed for a constant flow rate corresponding to the peak of the systolic phase of the cardiac cycle. Averaged velocity fields and turbulent quantities were determined for both, the base case, with no valve tilt, and for cases with an inclination of 4° and 8°, oriented at the four anatomical directions of the human body reference system, namely anterior, posterior, right and left. The results revealed the dominant flow patterns in the ascending aorta formed by a jet-like inlet flow impinging on the curved aorta right wall, inducing a significant eccentricity on the axial velocity profile. Regions of reverse flow were identified and linked to the abrupt area change associated with the typical reduced inlet diameter of TAVI implants. The impinging flow and wall curvature effects established circulation patterns defining a helical flow structure. The influence of the inlet flow orientation on the flow turbulent characteristics was assessed by the spatial evolution of the turbulent kinetic energy (TKE), Reynolds and viscous stresses. The maximum values of TKE were found around the inlet jet boundaries and concentrated in the neighborhood of the right aorta wall where the eccentric axial flow prevailed. Spatial distributions of the maximum Reynolds stresses were similar to the TKE distributions and presented maximum stresses typically one order of magnitude higher than the maximum average viscous shear stresses. Maximum average viscous stress distributions were revealed at the jet-like flow boundaries and in the vicinity of the right wall, displaying moderate stress levels that, according to the literature, can be sufficient to produce cell damage and platelet activation. The complex nature of the flow field was revealed by streamlines obtained from the measured flow fields, allowing the identification of the influence of the inlet flow orientation and tilt angle on the position of the stagnation point on the aorta right wall, as well as the angle of incidence of the jet-like flow on the wall. A simple model based on momentum balance was used to estimate the pressure increment on the wall due to flow impingement. The model captured the influence of the inlet flow orientation, indicating that pressure increases of the order of 40% in relation to the base case condition were obtained for the 8°, left inlet flow orientation.

Graphic abstract

中文翻译：

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主动脉瓣倾斜角对升主动脉血流模式的影响

经导管主动脉瓣植入术（TAVI）已成为诊断为主动脉瓣狭窄的高危患者的替代方法。与传统的开胸外科手术不同，TAVI手术有望在人工主动脉瓣展开角度上产生很小的变化。升主动脉中血流的血液动力学模式与许多心血管疾病的发展有关。然而，文献中很少有将主动脉瓣倾斜角与血流动力学效应相关的数据。在这项工作中，根据提交TAVI程序的特定患者的解剖结构，制作了由透明硅树脂制成的3D打印主动脉模型。立体粒子图像测速技术被用于测量沿上升主动脉在紧密间隔的横截面上的三分量速度场。针对对应于心动周期的收缩期峰值的恒定流速执行测量。确定了基本速度（无阀倾角）和倾斜度为4°和8°（面向人体参考系统的四个解剖方向）的情况下的平均速度场和湍流量， 右边和左边。结果表明，由射流状进气流撞击在弯曲的主动脉右壁上形成的升主动脉中的主导流型，在轴向速度剖面上引起了明显的偏心率。识别出逆流区域，并将其与与TAVI植入物的典型入口直径减小相关的突变区域变化联系起来。撞击流和壁曲率效应建立了定义螺旋流结构的循环模式。通过湍流动能（TKE），雷诺数和粘性应力的空间演化来评估入口流向对湍流特性的影响。在入口射流边界附近发现了TKE的最大值，并集中在偏心轴向流占优势的右主动脉壁附近。最大雷诺应力的空间分布与TKE分布相似，并且呈现出的最大应力通常比最大平均粘性剪切应力高一个数量级。在射流状流动边界和右壁附近显示出最大的平均粘性应力分布，显示出中等的应力水平，根据文献，这足以产生细胞损伤和血小板活化。流场的复杂性通过从测量的流场获得的流线显示出来，从而可以识别入口流的方向和倾斜角度对主动脉右壁停滞点位置以及角度的影响。喷射流在墙上的入射角。使用基于动量平衡的简单模型来估计由于流动冲击而在壁上产生的压力增量。该模型捕获了入口流向的影响，

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