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Research Papers

Stereoscopic Particle Image Velocimetry Analysis of Healthy and Emphysemic Alveolar Sac Models

[+] Author and Article Information
Emily J. Berg

Department of Mechanical Engineering,  Rochester Institute of Technology, 76 Lomb Memorial Drive, Building 9, Rochester, NY 14623ejb3439.rit@gmail.com

Risa J. Robinson

Department of Mechanical Engineering,  Rochester Institute of Technology, 76 Lomb Memorial Drive, Building 9, Rochester, NY 14623rjreme@rit.edu

J Biomech Eng 133(6), 061004 (Jun 21, 2011) (8 pages) doi:10.1115/1.4004251 History: Received May 04, 2011; Revised May 14, 2011; Posted May 17, 2011; Published June 21, 2011; Online June 21, 2011

Emphysema is a progressive lung disease that involves permanent destruction of the alveolar walls. Fluid mechanics in the pulmonary region and how they are altered with the presence of emphysema are not well understood. Much of our understanding of the flow fields occurring in the healthy pulmonary region is based on idealized geometries, and little attention has been paid to emphysemic geometries. The goal of this research was to utilize actual replica lung geometries to gain a better understanding of the mechanisms that govern fluid motion and particle transport in the most distal regions of the lung and to compare the differences that exist between healthy and emphysematous lungs. Excised human healthy and emphysemic lungs were cast, scanned, graphically reconstructed, and used to fabricate clear, hollow, compliant models. Three dimensional flow fields were obtained experimentally using stereoscopic particle image velocimetry techniques for healthy and emphysematic breathing conditions. Measured alveolar velocities ranged over two orders of magnitude from the duct entrance to the wall in both models. Recirculating flow was not found in either the healthy or the emphysematic model, while the average flow rate was three times larger in emphysema as compared to healthy. Diffusion dominated particle flow, which is characteristic in the pulmonary region of the healthy lung, was not seen for emphysema, except for very small particle sizes. Flow speeds dissipated quickly in the healthy lung (60% reduction in 0.25 mm) but not in the emphysematic lung (only 8% reduction 0.25 mm). Alveolar ventilation per unit volume was 30% smaller in emphysema compared to healthy. Destruction of the alveolar walls in emphysema leads to significant differences in flow fields between the healthy and emphysemic lung. Models based on replica geometry provide a useful means to quantify these differences and could ultimately improve our understanding of disease progression.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Silicone casts obtained post mortem from (left) healthy and (right) emphysemic lungs. Circled portions indicate the regions chosen for the experimental alveolar sac models. Red scale lines = 1 mm.

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Figure 2

Three dimensional reconstruction of the healthy (top row) and emphysemic (bottom row) alveolar casts from three different perspectives

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Figure 3

Rapid prototypes (left panels) and compliant models (right panels) used for experimental stereoPIV analysis. Top row represents the healthy model and bottom row is the emphysemic model. Approximate sizes are 33 mm by 41 mm for the healthy model and 31 mm by 35 mm for the emphysemic model.

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Figure 4

Experimental stereoPIV setup developed in our lab to obtain flow field measurements in the compliant alveolar sac models

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Figure 5

(Left) Locations of expected recirculating flow in the healthy model. (Right) Noncirculating streamlines occurring in the sixth location corresponding to planes illustrated in Fig. 6.

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Figure 6

Isometric view of the three-dimensional flow field vectors occurring in the healthy alveolar sac model for all six locations. Contours of velocity magnitude represent in vivo predictions determined by scaling the stereoPIV measurements.

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Figure 7

Isometric view of the three-dimensional flow field vectors occurring in the emphysemic alveolar sac model for all five locations. Contours of velocity magnitude represent in vivo predictions determined by scaling the stereoPIV measurements.

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Figure 8

Velocity field comparisons between healthy (top panel) and emphysemic (bottom panel) alveolar sac models at the 10th and 8th locations for H and E models, respectively. Contours of velocity magnitude represent in vivo predictions determined by dimensional analysis of stereoPIV measurements. Red scale lines = 1 mm in vivo dimensions.

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Figure 9

Velocity field comparisons between healthy (top panel) and emphysemic (bottom panel) alveolar sac models at the second locations for H and E models. Contours of velocity magnitude represent in vivo predictions determined by dimensional analysis of stereoPIV measurements. Red scale lines = 1 mm in vivo dimensions.

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Figure 10

Peclet number comparison between the healthy (H) and emphysemic (E) alveolar sac models. Dashed line indicates the critical Pe number which approximates the transition point between convective and diffusion dominated particle motion [23].

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