Lung deposition and extremely slow inhalations of particles. Limited effect of induced airway obstruction.

Studies of lung deposition and clearance have focused on the large airways. Still, lung diseases affect also the small airways. We have developed a method for selective particle deposition in the smallest ciliated airways. Eight healthy subject inhaled 6-micron radiolabelled test particles on 3 occasions at 0.05 L/s and retention was measured for 72 hours. At one occasion, the subjects inhaled the particles at a normal airway resistance. At a second occasion, a 2-3-fold increase in airway resistance was induced by a cholinergic provocation before inhalation of the particles. At a third occasion, a corresponding provocation was induced after inhalation of the particles. The percentage lung depositions were 76 +/- 7, 68 +/- 7, and 73 +/- 8 (mean +/- SD) for "normal airway resistance," "provocation before," and "provocation after" exposures, respectively. The lower value for the "provocation before" exposure was probably a result of increased mucociliary clearance, due to cholinergic stimulation, before the first measurements of radioactivity. The retentions at 24 hours were 51 +/- 7, 52 +/- 9, and 51 +/- 8 in percent of initial lung deposition for "normal airway resistance," "provocation before," and "provocation after" exposures, respectively. We conclude that our inhalation technique is useful in studying conditions in the bronchioles, as deposition is rather independent of airway resistance.