title: Interactions of airflow oscillation, tracheal inclination, and mucus elasticity significantly improve simulated cough clearance.
abstract: BACKGROUND
  Viscoelastic properties of simulated mucus, angle of tracheal inclination (theta), 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 degrees) and at increasing theta (15 degrees, 30 degrees, and 45 degrees), 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 theta 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 degrees 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).
authors.affiliation: Graduate Program in Biomedical Engineering, University of Nevada, Reno, NV 89557, USA.
authors.forename: Anpalaki J
authors.initials: AJ
authors.lastname: Ragavan
authors.forename: Cahit A
authors.initials: CA
authors.lastname: Evrensel
authors.forename: Peter
authors.initials: P
authors.lastname: Krumpe
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D003371:Cough / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D008954:Models, Biological; D009079:Mucociliary Clearance / Q000502:physiology*; D009093:Mucus / Q000378:metabolism*; D014132:Trachea / Q000378:metabolism / Q000503:physiopathology*; D014783:Viscosity