Chhabra Sudhaker, Prasad Ajay K
Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA.
J Biomech Eng. 2010 May;132(5):051009. doi: 10.1115/1.4001112.
The alveoli are the smallest units of the lung that participate in gas exchange. Although gas transport is governed primarily by diffusion due to the small length scales associated with the acinar region (approximately 500 microm), the transport and deposition of inhaled aerosol particles are influenced by convective airflow patterns. Therefore, understanding alveolar fluid flow and mixing is a necessary first step toward predicting aerosol transport and deposition in the human acinar region. In this study, flow patterns and particle transport have been measured using a simplified in-vitro alveolar model consisting of a single alveolus located on a bronchiole. The model comprises a transparent elastic 5/6 spherical cap (representing the alveolus) mounted over a circular hole on the side of a rigid circular tube (representing the bronchiole). The alveolus is capable of expanding and contracting in phase with the oscillatory flow through the tube. Realistic breathing conditions were achieved by exercising the model at physiologically relevant Reynolds and Womersley numbers. Particle image velocimetry was used to measure the resulting flow patterns in the alveolus. Data were acquired for five cases obtained as combinations of the alveolar-wall motion (nondeforming/oscillating) and the bronchiole flow (none/steady/oscillating). Detailed vector maps at discrete points within a given cycle revealed flow patterns, and transport and mixing of bronchiole fluid into the alveolar cavity. The time-dependent velocity vector fields were integrated over multiple cycles to estimate particle transport into the alveolar cavity and deposition on the alveolar wall. The key outcome of the study is that alveolar-wall motion enhances mixing between the bronchiole and the alveolar fluid. Particle transport and deposition into the alveolar cavity are maximized when the alveolar wall oscillates in tandem with the bronchiole fluid, which is the operating case in the human lung.
肺泡是肺中参与气体交换的最小单位。尽管由于与腺泡区域相关的长度尺度较小（约500微米），气体传输主要由扩散控制，但吸入气溶胶颗粒的传输和沉积受对流气流模式的影响。因此，了解肺泡内的流体流动和混合是预测人体腺泡区域气溶胶传输和沉积的必要第一步。在本研究中，使用了一个简化的体外肺泡模型来测量流动模式和颗粒传输，该模型由位于细支气管上的单个肺泡组成。该模型包括一个安装在刚性圆形管（代表细支气管）侧面圆孔上的透明弹性5/6球形帽（代表肺泡）。肺泡能够与通过管道的振荡流同步扩张和收缩。通过在生理相关的雷诺数和沃默斯利数下运行该模型，实现了逼真的呼吸条件。粒子图像测速技术用于测量肺泡内产生的流动模式。针对肺泡壁运动（非变形/振荡）和细支气管流动（无/稳定/振荡）组合得到的五种情况获取了数据。给定周期内离散点处的详细矢量图揭示了流动模式，以及细支气管流体向肺泡腔的传输和混合。对多个周期内随时间变化的速度矢量场进行积分，以估计颗粒向肺泡腔的传输和在肺泡壁上的沉积。该研究的关键结果是肺泡壁运动增强了细支气管与肺泡液之间的混合。当肺泡壁与细支气管流体同步振荡时，颗粒向肺泡腔的传输和沉积达到最大值，这是人体肺部的实际情况。
