Aerosol deposition in the airways with excessive mucus secretions was investigated utilizing an in vitro airway model lined with various mucus simulants of differing rheological properties. The airway model was made with a straight glass tube (1.0 cm ID and 20 cm in length) and positioned vertically. The mucus simulants were supplied into the tube at a constant rate and made to move upward through the tube as a thin layer (0.6-1.7 mm) undergoing a random wave motion by means of upward airflow. Aerosols (3.0 and 5.0-micron diam) were passed through the mucus-lined tube at flow rates of 0.33-1.17 l/s, and the deposition of the aerosols in the tube was determined by sampling the aerosols at the inlet and the outlet of the tube on filters. During the sampling, pressure drop across the tube model was also measured. Deposition efficiency in the 20-cm-long mucus-lined tube ranged from 13 to 92% with 3.0-micron-diam particles and from 66 to 98% with 5.0-micron-diam particles. This deposition was 25-300 times higher than that in the dry tube. The deposition was higher with increasing viscosity of mucus but was lower with increasing elasticity of mucus. Pressure drop across the mucus-lined tube was much higher than that in the dry tube, and the increase was more prominent with mucous layers with higher viscosity but lower elasticity values. Therefore, aerosol deposition showed a good positive relationship with pressure drop. However, percent increase of aerosol deposition in the mucus-lined tube was 2-5 times higher than that of pressure drop.(ABSTRACT TRUNCATED AT 250 WORDS)

As a model for the interaction between macrophages and mucus in the tracheobronchial tree, we incubated sheep alveolar macrophages in vitro with and without airway mucus from the same animal and tested their phagocytic function and rates of general protein synthesis. Airway mucus was obtained by tracheal suction after previous subcutaneous injection of the sheep with pilocarpine (0.5 mg/kg) and subsequently diluted. Pulmonary macrophages were obtained by saline lavage through a balloon-tipped fiber-optic bronchoscope. In incubated attached macrophages, phenylalanine incorporation into protein was inhibited 51% by mucus (P less than 0.001). Phagocytosis of 1.09-microns latex particles was inhibited 75% by mucus at nonsaturating levels of particles (P less than 0.001) and by 47% at saturating levels of particles (P less than 0.001). Inhibitory activity for protein synthesis and phagocytosis was retained in the 104,000 g supernatant fraction of whole mucus (sol), while the gel fraction inhibited phagocytosis only. This difference did not appear to be related to physical factors. We conclude that diluted airway mucus interferes with pulmonary macrophage function as assessed by rates of general protein synthesis and phagocytosis.