In this study, we investigate the steady inhalation, steady exhalation, and oscillatory flow in a realistic airway geometry for physiologically relevant regimes ranging from quiet breathing to respiration under high frequency ventilation (HFV). We use magnetic resonance velocimetry to characterize and quantify three-dimensional (3D) velocity fields in 3D printed replicas of realistic bronchial trees. Expanding on previous studies [Jalal et al., Exp. Fluids 57, 148 (2016); Jalal et al., Phys. Rev. Fluids 3, 103101 (2018)] which focused on respiration in planar double bifurcation geometries, we compare levels of axial and lateral dispersion, and find that they exceed those found in the idealized models. Furthermore, we find that the secondary flows in realistic airways propagate deep in the bronchial tree and are stronger during exhalation as compared to inhalation, while the mean flow topology does not vary significantly between the two steady regimes. Under HFV, we note significant regions of flow reversal during the inhalation-exhalation and exhalation-inhalation transitions. This is found to be due to a difference in impedance (dominated by inertance) in the different regions of the lung and results in an asynchronous ventilation between the upper and lower lobes. This phenomenon, also known as pendulluft is demonstrated experimentally for the first time, using both Eulerian velocity fields and Lagrangian pathlines. Secondary flows are stronger in exhalation compared to inhalation and at the peak of the ventilation cycle, match the steady cases although the flow topology can be significantly different. Finally, the cycle-averaged drift velocity suggests that steady streaming, while not negligible, is not the main transport mechanism during high-frequency ventilation.

中文翻译：

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人支气管树中的平稳和振荡流动

在这项研究中，我们调查了在现实的呼吸道几何结构中，从安静的呼吸到高频通气（HFV）呼吸的生理相关情况下的稳定吸入，稳定呼气和振荡流量。我们使用磁共振测速仪来表征和量化现实支气管树的3D打印副本中的三维（3D）速度场。扩展以前的研究[Jalal等。，  Exp。流体 57，148（2016）; Jalal等。，物理 流体修订版 3，103101（2018）]，重点研究了平面双分支几何结构中的呼吸，我们比较了轴向和横向弥散的水平，发现它们超过了理想模型中的水平。此外，我们发现，现实气道中的次要气流在支气管树中传播较深，并且在呼气过程中比吸气更强，而在两个稳定状态之间的平均流量拓扑没有明显变化。在HFV下，我们注意到在吸气-呼气和呼气-吸气过渡过程中有大量逆流区域。发现这是由于肺的不同区域中的阻抗差异（由惯性决定）所致，并导致上下叶之间的异步通气。这个现象，首次使用欧拉速度场和拉格朗日路径线对也称为pendulluft进行了实验验证。与吸入相比，次要流动在呼气方面更强，并且在通气周期的峰值时与稳定情况相匹配，尽管流动拓扑可能有很大不同。最后，周期平均漂移速度表明，稳定的流动虽然不能忽略，但不是高频通风过程中的主要传输机制。