Role of simulated repetitive coughing in mucus clearance.

The role of repetitive simulated coughing on the clearance of gel mucus simulant was investigated in vitro, by using a simulated cough machine. The repetition of cough induced a significant increase (p less than 0.01) in mucus simulant clearance (139.3 +/- 78.7 mm) in comparison to a single cough (24.9 +/- 27.5 mm). Moreover, the increase in frequency of the repetitive coughing induced a marked and significant increase in mucus simulant clearance (75.4 +/- 51.1 mm and 139.3 +/- 78.7 mm at 0.1 Hz and 1.6 Hz frequency, respectively). A significant (p less than 0.05) correlation was observed between the percentage increase of clearance and both shear-thinning index (r = 0.62) and the thixotropic index (r = 0.63). These results suggest that the shear-dependent properties of mucus, associated with a repetitive coughing, may increase the efficiency of mucus clearance by air flow mechanisms.