Abstract：
Aortic valve disease is often treated with bioprosthetic valves. An alternative treatment is aortic valve neocuspidization which is a relatively new reparative procedure whereby the three aortic cusps are replaced with patient pericardium or bovine tissues. Recent research indicates that aortic blood flow is disturbed, and turbulence effects have yet to be evaluated in either bioprosthetic or aortic valve neocuspidization valve types in patient-specific settings. The aim of this study is to better understand turbulence production in the aorta and evaluate its effects on laminar and turbulent wall shear stress. Four patients with aortic valve disease were treated with either bioprosthetic valves (n=2) or aortic valve neocuspidization valvular repair (n=2). Aortic geometries were segmented from magnetic resonance images (MRI), and 4D flow MRI was used to derive physiological inlet and outlet boundary conditions. Pulsatile large-eddy simulations were performed to capture the full range of laminar, transitional and turbulence characteristics in the aorta. Turbulence was produced in all aortas with highest levels occurring during systolic deceleration. In the ascending aorta, turbulence production is attributed to a combination of valvular skew, valvular eccentricity, and ascending aortic dilation. In the proximal descending thoracic aorta, turbulence production is dependent on the type of arch-descending aorta connection (e.g., a narrowing or sharp bend) which induces flow separation. Laminar and turbulent wall shear stresses are of similar magnitude throughout late systolic deceleration and diastole, although turbulent wall shear stress magnitudes exceed laminar wall shear stresses between 27.3% and 61.1% of the cardiac cycle. This emphasises the significance of including turbulent wall shear stress to improve our comprehension of progressive arterial wall diseases. The findings of this study recommend that aortic valve treatments should prioritise minimising valvular eccentricity and skew in order to mitigate turbulence generation.
摘要：
主动脉瓣疾病通常用生物人工瓣膜治疗。另一种治疗方法是主动脉瓣新穿孔术，这是一种相对较新的修复程序，其中三个主动脉瓣由患者心包或牛组织代替。最近的研究表明，主动脉血流受到干扰，在特定于患者的环境中，尚未对生物瓣膜或主动脉瓣新刀瓣类型的湍流效应进行评估。这项研究的目的是更好地了解主动脉中的湍流产生，并评估其对层流和湍流壁切应力的影响。4例主动脉瓣疾病患者接受了生物人工瓣膜（n=2）或主动脉瓣新囊化瓣膜修复（n=2）。从磁共振图像（MRI）分割主动脉几何结构，和4D流MRI用于推导生理入口和出口边界条件。进行了脉动大涡模拟以捕获层流的全部范围，主动脉的过渡性和湍流特征。所有主动脉都产生湍流，在收缩期减速期间出现最高水平。在升主动脉中,湍流的产生归因于瓣膜偏斜的组合，瓣膜偏心,升主动脉扩张.在近端降主动脉，湍流的产生取决于弓降主动脉连接的类型(例如，狭窄或急剧的弯曲）引起流动分离。在整个收缩后期减速和舒张期，层流和湍流壁剪切应力的幅度相似。尽管湍流壁切应力大小超过层流壁切应力，但在心动周期的27.3％至61.1％之间。这强调了包括湍流壁切应力以提高我们对进行性动脉壁疾病的理解的重要性。这项研究的结果表明，主动脉瓣治疗应优先考虑最小化瓣膜偏心和偏斜，以减轻湍流的产生。
