基于Echo-PIV的狭窄主动脉模型中的涡旋动力学和输运现象
Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV
摘要：
在这项工作中，我们提出了一种新的方法，结合超声与欧拉和拉格朗日描述符，分析血流动力学和流体传输狭窄的主动脉模型的形态，机械和光学特性接近真实的动脉。为此，涡量，粒子停留时间（PRT），粒子的最终位置（FP）和有限时间李雅普诺夫指数（FTLE）计算从实验流体速度场获得使用超声粒子成像测速（Echo-PIV）。在实验中，使用CT图像创建具有与真实动脉相同的机械特性的0%、35%和50%闭塞度的降主动脉的形态逼真模型。每个模型都连接到带有脉动可编程泵的回路，该泵模拟生理流量和压力条件。脉动频率设定为0.9 Hz（55 bpm），上游峰值雷诺数（Re）从1100变更为2000。狭窄后区域的流动由两个主要结构组成：狭窄喉部上方的高速射流和狭窄后方的回流区，在回流区形成和脱落涡流。我们的特点是旋涡运动学表明，旋涡传播速度增加与Re。此外，从FTLE领域，我们确定了拉格朗日相干结构（即材料障碍），决定运输背后的狭窄。这些障碍的大小和强度增加Re和闭塞程度。最后，从PRT和FP，我们发现，独立于Re，相同量的液体在一个以上的脉动周期内保留在狭窄处，这与较大的FTLE值相结合，可以提供一种了解狭窄生长的替代方法。
英文摘要：
In this work, we propose a novel approach which combines ultrasound with Eulerian and Lagrangian descriptors, to analyse blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to 0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases with Re. Moreover, from the FTLE field we identified Lagrangian Coherent Structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased with Re and the occlusion degree. Finally, from the PRT and FP, we showed that independently of Re, the same amount of fluid remains on the stenosis over more than a pulsatile period, which combined with large FTLE values may provide an alternative way to understand stenosis growth.
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