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Research Papers

# Flow and Particle Dispersion in a Pulmonary Alveolus—Part I: Velocity Measurements and Convective Particle Transport

[+] Author and Article Information
Sudhaker Chhabra

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716prasad@udel.edu

1

Corresponding author.

J Biomech Eng 132(5), 051009 (Mar 30, 2010) (12 pages) doi:10.1115/1.4001112 History: Received June 15, 2009; Revised January 13, 2010; Posted January 27, 2010; Published March 30, 2010; Online March 30, 2010

## Abstract

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 $(∼500 μm)$, 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.

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## Figures

Figure 1

Experimental model: (a) schematic of the single alveolus attached to bronchiole, (b) photograph of the model, and (c) raw PIV image of the alveolus

Figure 2

Experimental setup

Figure 3

Case A: velocity map for steady bronchiole flow over a non-deforming alveolus: (a) close-up of the upper half of the cavity highlighting the secondary vortex, and (b) schematic showing streamlines for the shear layer, and primary and secondary vortices

Figure 4

Case B: velocity fields for oscillating bronchiole flow over a nondeforming alveolus

Figure 5

Case C: velocity fields for an oscillating alveolus without an imposed bronchiole flow

Figure 6

Case D: velocity fields for oscillating alveolus with steady bronchiole flow

Figure 7

Case E: velocity fields for oscillating alveolus with oscillating bronchiole flow

Figure 8

Particle maps for case C after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 9

Particle transport statistics as a function of breathing cycle for case C

Figure 10

Particle maps for case D after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 11

Particle transport statistics as a function of breathing cycle for case D

Figure 12

Particle maps for case E after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 13

Particle transport statistics as a function of breathing cycle for case E

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