The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

INCREASED THICKNESS AND VOLUME OF MUCUS DURING AIRWAY DISEASES FACILITATE ITS CLEARANCE DURING COUGH.

Anpalaki J. Ragavan1, Cahit A. Evrensel1,2, Peter Krumpe1,3; 1Biomedical Engineering, University of Nevada, Reno, Reno, NV; 2Mechanical Engineering, University of Nevada, Reno, Reno, NV; 3VA Sierra Nevada Health Care Systems, 1000 Locust Street, Reno, NV

BACKGROUND During airway diseases (asthma, cystic fibrosis and/or COPD) when mucus clearance by cilia is impaired, clearing of purulent mucus by cough becomes vital.In all these diseases volume and thickness of secretions in airways is considerably increased, the effect of which on cough mechanics is unclear. Mucus viscosity also considerably increases with inflammation. We hypothesize that larger the amount of mucus larger may be the differences in velocities of air and mucus leading to larger agitation and displacement consequent upon air mucus interaction. Increased agitation in mucus during cough may lead to increased viscous energy losses adding resistance, which may be reduced by inducing elastic forces in the mucus. METHODS Two groups of mucus (4 per group) similar to airway mucus of patients with airway diseases were prepared by cross-linking 0.01 molar(M) Locust Bean Gum (Sigma, St Louis, MO) solution with different amounts of 0.02M Borax(Na2B4O7[10H2O]) solution titrated with sucrose and/or food starch solutions. The ratio of storage modulus (G’ measure of elasticity) to viscosity(n’) (measured at 1Hz) was varied between 15 and 100 while keeping surface tension (62.6 ± 0.1dyne/cm for group1 and 67.8 ± 2,3dyne/cm for group2), and adhesivity (32.96 ± 1.94ergs/cm2 for group1 and 19.75 ± 0.74ergs/cm2 for group2) within group constant. The G’ and n’ were measured at room temperature (24 ± 5oC) with a rheometer (AR1500, TA Instruments, New Castle, DW). Coughs were generated in a Plexiglas adult model trachea by diverting a 300ms burst of air using a computer controlled solenoid valve after placing mucus in four volumes (0.2mL, 0.4mL, 0.7mL or 1.0mL) inside trachea. Displacements of mucus were measured during coughs at each of two constant velocities (12m/s, and 15m/s). Cough velocity was measured by a differential pressure transducer (Validyne, Northridge, CA) and pneumotachygraph. RESULTS Displacement of mucus increased with volume of mucus inside trachea at all G’/n’ ratio at both velocities (Figure 1). At 12m/s the volume required to initiate displacement was larger than at 15m/s at all G’/n’. Displacement of mucus increased with G’/n’. The increase was larger, larger the volume of mucus. CONCLUSIONS Mucus hyper secretion during airway diseases may depend on patient’s ability to generate adequate cough velocities. Increased elasticity of mucus during diseases may reduce energy losses at high air flows, increasing displacement. Sponsored Research - None Figure 1: Simulated airway mucus volume versus displacement shown at two cough velocities 12m/s(A) and 15m/s(B) at five G'/n' values