Tsuda A, Henry F S, Butler J P
Physiology Program, Harvard School of Public Health, Boston, Massachusetts, USA.
J Appl Physiol (1985). 1995 Sep;79(3):1055-63. doi: 10.1152/jappl.1995.79.3.1055.
We examined the effects of rhythmic expansion of alveolar walls on fluid mechanics in the pulmonary acinus. We generated a realistic geometric model of an alveolated duct that expanded and contracted in a geometrically similar fashion to simulate tidal breathing. Time-dependent volumetric flow was generated by adjusting the proximal and distal boundary conditions. The low Reynolds number velocity field was solved numerically over the physiological range. We found that for a given geometry, the ratio of the alveolar flow (QA) to the ductal flow (QD) played a major role in determining the flow pattern. For larger QA/QD (as in the distal region in the acinus), the flow in the alveolus was largely radial. For small QA/QD (as in the proximal region in the acinus), the flow in the alveolus was slowly rotating and the velocity field near the alveolar opening was complex with a stagnation saddle point typical of chaotic flow structures. Performing Lagrangian fluid particle tracking, we demonstrated that in such a flow structure the motion of fluid could be highly complex, irreversible, and unpredictable even though it was governed by simple deterministic equations. These are the characteristics of chaotic flow behavior. We conclude that because of the unique geometry of alveolated duct and its time-dependent motion associated with tidal breathing, chaotic flow and chaotic mixing can occur in the lung periphery. Based on these novel observations, we suggest a new approach for studying acinar fluid mechanics and aerosol kinetics.
我们研究了肺泡壁的节律性扩张对肺腺泡内流体力学的影响。我们构建了一个逼真的肺泡管几何模型，该模型以几何相似的方式进行扩张和收缩，以模拟潮气呼吸。通过调整近端和远端边界条件来生成随时间变化的体积流量。在生理范围内对低雷诺数速度场进行了数值求解。我们发现，对于给定的几何形状，肺泡流量（QA）与导管流量（QD）的比值在确定流动模式中起主要作用。对于较大的QA/QD（如在腺泡的远端区域），肺泡内的流动主要是径向的。对于较小的QA/QD（如在腺泡的近端区域），肺泡内的流动是缓慢旋转的，并且肺泡开口附近的速度场很复杂，具有典型的混沌流动结构的停滞鞍点。通过进行拉格朗日流体粒子追踪，我们证明在这样的流动结构中，即使流体运动由简单的确定性方程控制，其运动也可能高度复杂、不可逆且不可预测。这些是混沌流动行为的特征。我们得出结论，由于肺泡管独特的几何形状及其与潮气呼吸相关的随时间变化的运动，在肺周边可能会发生混沌流动和混沌混合。基于这些新的观察结果，我们提出了一种研究腺泡流体力学和气溶胶动力学的新方法。
