EFFECT OF ADRENERGIC-STIMULATION ON CLEARANCE FROM SMALL CILIATED AIRWAYS IN HEALTHY-SUBJECTS

Mucociliary transport is an important clearance mechanism of larger ai rways, but in the smallest ciliated airways (bronchioles) if may be le ss effective. The present study aimed at investigating whether clearan ce from the bronchioles in subjects with healthy airways was stimulate d by an adrenergic agonist (terbutaline sulphate). Tracheobronchial cl earance was studied twice in 10 healthy subjects after inhalation of 6 -mu m (aerodynamic diameter) monodisperse Teflon particles labeled wit h In-111. At one exposure, oral treatment with terbutaline sulphate, K nown to stimulate clearance in large airways, began immediately after inhalation of he particles. The other exposure was a control measureme nt. The particles were inhaled at an extremely slow flow, 0.05 L/s, wh ich gave deposition mainly in the small ciliated airways (bronchioles) . Lung retention was measured at 0, 24, 48, and 72 h. Clearance was si gnificant every 24 h for both exposures (p <.05, two-tailed paired t-t est), with similar fractions of retained particles at all time points. During treatment with terbutaline sulphate, the subjects' pulse rates tended to be higher, but clearance rates did not increase. We found, as expected, no significant correlation between lung retention and lun g function in either exposure. This study shows that an adrenergic ago nist does not significantly influence overall clearance from the bronc hiolar region in healthy subjects. This suggests that mucociliary tran sport does not significantly contribute to clearance from the smallest ciliated airways. Other mechanisms may be more important for the tran sportation of mucus from these airways.