Salameh Elie, Saade Charbel, Oweis Ghanem F
Department of Mechanical Engineering, M.S. Faculty of Engineering & Architecture, American University of Beirut, PO Box 11-0236, Beirut, 1107-2020, Lebanon.
Medical Imaging Sciences, Faculty of Health Sciences, American University of Beirut, PO Box 11-0236, Beirut, 1107-2020, Lebanon.
Cardiovasc Eng Technol. 2019 Jun;10(2):314-328. doi: 10.1007/s13239-019-00407-4. Epub 2019 Feb 25.
In a curved vessel such as the aortic arch, the velocity profile closer to the aortic root is normally skewed towards the inner curvature wall, while further downstream along the curve, the velocity profile becomes skewed towards the outer wall. In an aortic dissection (AD) disease, blood velocities in the true lumen (TL) and false lumen (FL) are hypothesized to depend on the proximity of the entry tear to the root of aortic arch. Faster velocity in the FL can lead to higher hemodynamic loading, and pose tearing risk. Furthermore, the luminal velocities control the perfusion rate of radiological contrast media during diagnostic imaging. The objective in this study is to investigate the effect of AD disease morphology and configuration on the blood velocity field in the TL and FL, and on the relative perfusion of radiological enhancement agents through the dissection.
Eight in vitro models were studied, including patent and non-patent FL configurations. Particle image velocimetry (PIV) was used to quantify the AD velocity field, while laser-induced fluorescence (LIF) was implemented to visualize dynamical flow phenomena and to quantify the perfusion of injected dye, in mimicry of contrast-enhanced computed tomography (CT).
The location of the proximal entry tear along the aortic arch in a patent FL had a dramatic impact on whether the blood velocity was higher in the TL or FL. The luminal velocities were dependent on the entry/reentry tear size combination, with the smaller tear (whether distal or proximal) setting the upper limit on the maximal flow velocity in the FL. Upon merging near the distal reentry tear, the TL/FL velocity differential gave rise to the roll up and shedding of shear layer vortices that convected downstream in close proximity to the wall of the non-dissected aorta. In a non-patent FL, the flow velocity was practically null with all the blood passing through the TL. LIF imaging showed much slower perfusion of contrast dye in the FL compared to the TL. In a patent FL, however, dye had a comparable perfusion rate appearing around the same time as in the TL.
Blood velocities in the TL and FL were highly sensitive to the exact dissection configuration. Geometric case A1R, which had its proximal entry tear located further downstream along the aortic arch, and had its entry and reentry tears sufficiently sized, exhibited the highest FL flow velocity among the tested models, and it was also higher than in the TL, which suggest that this configuration had elevated hemodynamic loading and risk for tearing. In contrast-enhanced diagnostic imaging, a time-delayed acquisition protocol is recommended to improve the detection of suspected cases with a non-patent FL.
在诸如主动脉弓这样的弯曲血管中，靠近主动脉根部的速度剖面通常向内侧弯曲壁倾斜，而沿着曲线进一步向下游，速度剖面则向外侧壁倾斜。在主动脉夹层（AD）疾病中，真腔（TL）和假腔（FL）中的血流速度被认为取决于入口撕裂与主动脉弓根部的距离。假腔中较快的速度会导致更高的血流动力学负荷，并带来撕裂风险。此外，管腔内速度控制着诊断成像期间放射学造影剂的灌注速率。本研究的目的是研究AD疾病形态和结构对真腔和假腔中血流速度场以及通过夹层的放射学增强剂相对灌注的影响。
研究了八个体外模型，包括有血流和无血流的假腔配置。粒子图像测速技术（PIV）用于量化AD速度场，而激光诱导荧光（LIF）用于可视化动态流动现象并量化注入染料的灌注，以模拟对比增强计算机断层扫描（CT）。
在有血流的假腔中，近端入口撕裂沿主动脉弓的位置对真腔或假腔中血流速度是否更高有显著影响。管腔内速度取决于入口/再入口撕裂大小组合，较小的撕裂（无论是远端还是近端）设定了假腔中最大流速的上限。在远端再入口撕裂附近合并时，真腔/假腔速度差导致剪切层涡旋的卷起和脱落，这些涡旋在靠近未夹层主动脉壁的下游对流。在无血流的假腔中，流速实际上为零，所有血液都通过真腔。LIF成像显示，与真腔相比，假腔中造影剂的灌注要慢得多。然而，在有血流的假腔中，染料的灌注速率相当，出现时间与真腔大致相同。
真腔和假腔中的血流速度对确切的夹层结构高度敏感。几何病例A1R的近端入口撕裂位于主动脉弓更下游，其入口和再入口撕裂大小足够，在测试模型中表现出最高的假腔流速，并且也高于真腔，这表明这种结构具有更高的血流动力学负荷和撕裂风险。在对比增强诊断成像中，建议采用延时采集方案以提高对无血流假腔疑似病例的检测。
