Ineffectiveness of cough for enhancing mucus clearance in asymptomatic smokers

Using monodisperse aerosols radiolabeled with 99mTc, we studied the effectiveness of cough and rapid inhalations for clearing mucus in ten asymptomatic smokers. On three separate study days, each subject breathed 5 microns (MMAD) 99mTc-iron oxide particles under controlled breathing conditions. While seated in front of a gamma camera, retention (R) of lung activity (measured as a percent of initial activity) was measured over the initial 2 h and again at 24 h following particle inhalation. On the control day the subject sat quietly in front of the camera, while on the cough day each subject performed 60 controlled coughs during the first hour of retention measurements, and on the rapid inhalation study day each subject performed 90 rapid inhalations during the first hour of retention measurements. Because breathing patterns were controlled during particle inhalation, initial lung deposition patterns were matched on control, cough, and rapid inhalation study days. By paired analysis, retentions at both 1 and 2 h (R1 and R2) for the cough and rapid inhalation measurements were not significantly different from control (mean control R1 = 69 percent; mean cough R1 = 66 percent; mean rapid inhalation R1 = 66 percent, NS; and mean control R2 = 59 percent, mean cough R2 = 55 percent; mean rapid inhalation R2 = 54 percent, NS). Retention at 24 h (R24) was not significantly different between cough, rapid inhalation, and control measurements (mean cough R24 = 15 percent, mean rapid inhalation R24 = 14 percent, mean control R24 = 17 percent). In other words, these young smokers with normal pulmonary function were unable to enhance their rate of mucus clearance by coughing. The inability of these young smokers to enhance their mucus clearance by cough suggests a change in the mucociliary apparatus from normal.