Respiratory mucus from asymptomatic smokers is better hydrated and more easily cleared by mucociliary action

We compared the physical and transport properties of tracheal mucus collected from 16 asymptomatic smokers and from 18 nonsmokers. The smokers produced a larger volume of mucus (wet weight 18.6 versus 11.2 mg; p = 0.04) with a lower solids content (11.5 versus 16.3%; p = 0.02) and a lower modulus of rigidity (log G* 2.37 versus 2.62; p = 0.04). Although the smokers mucus had a 40% faster mucociliary transport rate on the frog palate (p = 0.04), the cough clearability was nearly identical to the mucus from nonsmokers. The differences are similar to those observed in rats or dogs chronically exposed to cigarette smoke. These data suggest both a quantitative and a qualitative difference in the composition of mucus from asymptomatic smokers. The increased volume of a watery mucus with increased mucociliary clearability may help to protect the airways from the injurious effects of inhaled smoke.