Inhaled mannitol changes the sputum properties in asthmatics with mucus hypersecretion

BACKGROUND AND OBJECTIVES: Most asthmatics with mucus hypersecretion have difficulty in clearing their secretions so that mucus plugs and airway obstruction are commonly present. Inhaled mannitol facilitates clearance of mucus. This study investigated the changes in the physical properties of sputum in response to mannitol in asthmatics with chronic cough and sputum production. METHOD: Sputum was collected from 12 asthmatics (26-73 year), lifelong non-smokers, at baseline, after eformoterol (24 mug) and after mannitol on each of four visits. Inhaled mannitol doses were: 635 mg (Visit 1), 240 mg (Visit 2), 360 mg (Visit 3) and 360 mg in the presence of montelukast (Visit 4). Eformoterol was inhaled before mannitol on each visit to prevent bronchoconstiction. Sputum measurements included viscosity, elasticity, surface tension, contact angle-glass and percentage solids. RESULTS: There were no significant differences between the sputum properties at baseline and after eformoterol. Mannitol (360 mg) reduced the baseline (mean +/- SEM) elasticity from 29.9 +/- 4.5 to 15.1 +/- 1.4 Pa (P < 0.0001), viscosity from 18.4 +/- 3.2 to 8.1 +/- 1.2 Pa (P < 0.0001) at 1 rad/ s, surface tension from 92.1 +/- 2.2 to 81.9 +/- 2.5 mN/m (P < 0.0001), contact angle-glass from 57.5 +/- 3.2 to 49.6 +/- 2.0 degrees (P < 0.0001), and percentage solids from 6.9 +/- 0.7 to 5.7 +/- 0.4% (P < 0.0001). All doses of mannitol reduced the sputum properties similarly and no property was further reduced by montelukast (P > 0.4). CONCLUSION: Inhaled mannitol reduced the viscoelasticity, surface tension, contact angle and the solids content of sputum in asthmatics with chronic cough and sputum production, consistent with the osmotic effect of mannitol causing water efflux in the airway lumen.