Measurement of tracheal and bronchial mucus velocities in man: relation to lung clearance

Abstract

Techniques utilizing the inhalation and deposition of radioactive particles followed by .gamma. camera imaging were applied to the problem of differentiating mucociliary function at various generations of the tracheobronchial tree in man. Quantitative values for linear velocities of mucus movement in the trachea and large bronchi could be compared with whole or peripheral (small bronchi) lung clearance rates. Mucus velocity in main bronchi averaged 2.4 mm/min and correlated (r [correlation coefficient] = 0.81) with tracheal mucus velocity, which averaged 5.5 mm/min. Subjects removed an average of 68% of their total deposition during the initial 24 h after inhalation; particles cleared the ciliated airways at a mean rate of 0.51%/min. .beta.-Adrenergic (.beta.-AD) aerosols enhanced mucociliary function by increasing central airway mucus transport (bronchial and tracheal velocities were raised 156 and 37%, respectively) and peripheral lung clearance (by at least 40%). Whole lung clearance correlated better with main bronchial velocities (r = 0.71) than did peripheral lung clearance (r = 0.27). The ratio of tracheal to bronchial mucus velocities in the normal lung apparently equals 2.7. Tracheal mucus velocities are normally close to the maximum that could be stimulated by .beta.-AD, and main bronchi have velocities of only 40% of maximum. Peripheral ciliated airways increase mucus clearance after .beta.-AD and contribute to the overall effect of .beta.-AD on whole lung clearance.