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Original Research: COUGH |

Interactions of Airflow Oscillation, Tracheal Inclination, and Mucus Elasticity Significantly Improve Simulated Cough Clearance

Anpalaki J. Ragavan, MS; Cahit A. Evrensel, PhD; Peter Krumpe, MD, FCCP
Author and Funding Information

From the Graduate Program in Biomedical Engineering (Ms Ragavan, Drs Evrensel and Krumpe), the Department of Mechanical Engineering (Dr Evrensel), and the School of Medicine (Dr Krumpe), University of Nevada, Reno, NV.

Correspondence to: Cahit A. Evrensel, PhD, Associate Professor, Department of Mechanical Engineering, MS 312, University of Nevada, Reno, NV 89557; e-mail: cahit@unr.edu


Funding/Support: This study was funded by the Department of Mechanical Engineering, Graduate Program of Biomedical Engineering at University of Nevada, Reno; the Department of Internal Medicine at University of Nevada School of Medicine; and the Medical and Research Services at the Veterans Affairs Sierra Nevada Health Care System, Reno, NV.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(2):355-361. doi:10.1378/chest.08-2096
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Background:  Viscoelastic properties of simulated mucus, angle of tracheal inclination (θ), and high-frequency airflow oscillations on median displacement of simulated mucus during simulated cough were investigated in this study.

Methods:  Mucus simulants with viscoelastic properties similar to healthy individuals and patients with COPD were prepared using locust bean gum (LBG)-water solution (0.38 g LBG in 100 mL water) cross-linked with 3-mL and 12-mL borax-water solution (0.02 M), respectively. Aliquots of 0.3 mL of simulants were placed on a dry Plexiglas insert inside a d-shaped clear Plexiglas tracheal model. Movement of aliquots of mucus simulants was measured during cough of 0.3 s duration. Cough velocities studied (5-30 m/s) are typical of patients with weak expiratory muscles and airway obstruction. Studies were conducted with tracheal model placed horizontally (0°) and at increasing θ (15°, 30°, and 45°), with and without superimposed airflow oscillations during coughs. Effects of different parameters and their interactions on displacements of aliquots were compared using analysis of covariance (n = 849).

Results:  Significant positive nonlinear associations existed between displacement and cough velocity for both 3-mL and 12-mL simulants (P < .0001). Displacement was greatest for the cohesive 12-mL simulant at all cough velocities. Displacement increased significantly (P < .0001) as θ was increased for both types of simulants. Largest displacements at low cough velocities occurred with 12-mL simulant in the presence of oscillations at 45° angle.

Conclusions:  Results support the use of airflow oscillations and sitting upright to facilitate mucus displacement during cough, particularly with thick, elastic mucus found in patients with COPD (P < .0001).

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