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 me thod for selective particle deposition in the smallest ciliated airways. Ei ght healthy subject inhaled 6-mu m radiolabelled test particles on 3 occasi ons at 0.05 L/s and retention was measured for 72 hours. At one occasion, t he subjects inhaled the particles at a normal airway resistance. At a secon d occasion, a 2-3-fold increase in airway resistance was induced by a choli nergic 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 (mea n +/- SD) for "normal airway resistance," "provocation before," and "provoc ation 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 radioactiv ity. The retentions at 24 hours were 51 +/- 7, 52 +/- 9, and 51 +/- 8 in pe rcent of initial lung deposition for "normal airway resistance," "provocati on before," end "provocation after" exposures, respectively. We conclude th at our inhalation technique is useful in studying conditions in the bronchi oles, as deposition is rather independent of airway resistance.