Laboratorio de Acústica Ultrasonora, Instituto de Física, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400, Montevideo, Uruguay.
Grupo de Dinámica Cardiovascular, Universidad Pontificia Bolivariana, Medellín, Colombia.
Phys Med Biol. 2021 Feb 26;66(5). doi: 10.1088/1361-6560/abd670.
Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze 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 () 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. 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 withand the occlusion degree. Finally, from the PRT and FP maps, we showed that independently of, the same amount of fluid remains on the stenosis over more than a pulsatile period.
动脉粥样硬化是最致命的心血管疾病。随着疾病的发展，动脉内部的狭窄会逐渐增大，阻塞管腔并改变血流。分析流动动力学可以更深入地了解狭窄的演变。在这项工作中，我们结合了欧拉和拉格朗日描述符来分析形态、力学和光学特性与真实动脉相近的狭窄主动脉模型中的血流动力学和流体输运。为此，我们从使用超声粒子成像速度测量法（Echo-PIV）获得的实验流体速度场中计算了涡度、粒子停留时间（PRT）、粒子最终位置（FP）和有限时间拉普拉斯指数（FTLE）。对于实验，我们使用 CT 图像创建了降主动脉的形态逼真模型，阻塞程度分别为 0%、35%和 50%，其力学特性与真实动脉相同。每个模型都与一个带有脉动可编程泵的回路相连，该泵模拟生理流动和压力条件。脉动频率设置为≈0.9 Hz（55 bpm），上游峰值雷诺数（）从 1100 增加到 2000。狭窄后的流场由两个主要结构组成：狭窄喉口上方的高速射流和狭窄后的回流区，其中形成并脱落了旋涡。我们对旋涡运动学进行了特征描述，表明旋涡传播速度随增加。此外，从 FTLE 场中，我们确定了拉格朗日相干结构（即物质屏障），这些结构决定了狭窄后的输运。这些屏障的大小和强度随增加，而随阻塞程度增加。最后，从 PRT 和 FP 图中，我们发现无论如何，在脉动周期以上，相同数量的流体仍留在狭窄处。
