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Research Papers

Flow Field Analysis in Expanding Healthy and Emphysematous Alveolar Models Using Particle Image Velocimetry

[+] Author and Article Information
Jessica M. Oakes, Steven Day

Department of Mechanical Engineering, Rochester Institute of Technology, Rochester, NY 14623

Steven J. Weinstein

Department of Chemical Engineering, Rochester Institute of Technology, Rochester, NY

Risa J. Robinson1

Department of Mechanical Engineering, Rochester Institute of Technology, Rochester, NYrjreme@rit.edu

1

Corresponding author.

J Biomech Eng 132(2), 021008 (Jan 29, 2010) (9 pages) doi:10.1115/1.4000870 History: Received February 04, 2009; Revised October 02, 2009; Posted December 22, 2009; Published January 29, 2010; Online January 29, 2010

Particulates that deposit in the acinus region of the lung have the potential to migrate through the alveolar wall and into the blood stream. However, the fluid mechanics governing particle transport to the alveolar wall are not well understood. Many physiological conditions are suspected to influence particle deposition including morphometry of the acinus, expansion and contraction of the alveolar walls, lung heterogeneities, and breathing patterns. Some studies suggest that the recirculation zones trap aerosol particles and enhance particle deposition by increasing their residence time in the region. However, particle trapping could also hinder aerosol particle deposition by moving the aerosol particle further from the wall. Studies that suggest such flow behavior have not been completed on realistic, nonsymmetric, three-dimensional, expanding alveolated geometry using realistic breathing curves. Furthermore, little attention has been paid to emphysemic geometries and how pathophysiological alterations effect deposition. In this study, fluid flow was examined in three-dimensional, expanding, healthy, and emphysemic alveolar sac model geometries using particle image velocimetry under realistic breathing conditions. Penetration depth of the tidal air was determined from the experimental fluid pathlines. Aerosol particle deposition was estimated by simple superposition of Brownian diffusion and sedimentation on the convected particle displacement for particles diameters of 100–750 nm. This study (1) confirmed that recirculation does not exist in the most distal alveolar regions of the lung under normal breathing conditions, (2) concluded that air entering the alveolar sac is convected closer to the alveolar wall in healthy compared with emphysematous lungs, and (3) demonstrated that particle deposition is smaller in emphysematous compared with healthy lungs.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 2

Depth (D) to MD ratio of alveolar sac models and those reported by Klingele and Staub (22) and Mercer (24)

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Figure 3

Experimental unsteady flow rate curve used to simulate breathing conditions in healthy alveolar sac model. Curve is based on a change in volume of 13.29 ml and a breathing cycle of 8 s. Emphysema flow rate graph is similar with a change in volume of 18.15 ml and a breathing cycle of 11 s. Solid line is flow rate measured from the spirometer. The dashed line is the two piece polynomial curve fitted to the spirometer data.

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Figure 4

Schematic of the experimental setup

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Figure 5

Streamlines in the top left healthy alveolus model at maximum flow rate (1.2 s into the breathing cycle)

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Figure 6

Experimental velocity magnitude at high inlet flow rate (7.13 ml/s and 7.09 ml/s for H and E, respectively) for (a) H at 1.43 s and (b) E at 1.95 s for the top half of the model

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Figure 8

Distance traveled by aerosol particles for a given number of 3 s inhalations, compared with the maximum distance required to reach the alveolar wall (using pathline 6 for H and pathline 5 for E) for combination sedimentation and diffusion (28)

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Figure 1

Alveolar sac model geometries for healthy side (a) and top (b) view and emphysema side (c) and top (d) view. Measurements are shown in Table 1.

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Figure 7

Pathlines starting at duct entrance in healthy (a) and emphysemic (b) alveolar sac models plotted over one complete breathing cycle

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