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.
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).
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.
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).