RETENTION OF PARTICLES INHALED IN BOLI WITH AND WITHOUT INDUCED BRONCHOCONSTRICTION

Large lung retentions (up to 50%) of particles less than or equal to 4 mu m inhaled with a bolus technique at a penetration depth less than dead space have been reported to occur after 24 h, This retention may be due to retarded clearance of particles deposited in the airways of the tracheobronchial tract; an alternative explanation, could be that particles are deposited in the alveolar region. The purpose of the pre sent study was to confirm the occurrence of retained fractions and to study the influence of a cholinergic drug, which is assumed to give a more central particle deposition, on these retentions in human lungs a fter shallow aerosol bolus inhalation. Twelve healthy subjects inhaled , with a bolus technique, monodisperse Teflon particles (2.4 mu m geom etric diameter, 3.5 mu m aerodynamic diameter), labeled with In-111. T he volumetric lung depth of the inspired boils was around GO mt and fl ow rate was about 300 mL/s. Six subjects inhaled the test particles af ter a provocation with a cholinergic aerosol, which induced a threefol d increase in airway resistance. The other siv subjects inhaled a chol inergic aerosol after inhalation of the test particles or inhaled no c holinergic aerosol at all. Radioactivity in the body was measured afte r 0.5, 24, 48, and 72 h with a whole-body scunner with three 127 x 101 -mm NaI detectors, The investigation confirmed results obtained earlie r by a group in Frankfurt claiming that great retentions occur after 2 4 h. Thr retentions tended to be lower in the group receiving a bronch oconstricting drug before the bolus inhalations. There was a significa nt lung clearance of particles between 24 and 72 h, in contrast to the findings in earlier studies in healthy subjects and asthmatics who in haled Teflon particles in large volumes. On the other hand, the cleara nce agreed well with the clearance in healthy subjects with extensive deposition of Teflon particles in the small ciliated airways, obtained by means of an extremely low inhalation flow rate. The results sugges t that a considerable fraction of the particles in the bolus inhalatio n haze been deposited in small ciliated airways in which the mucocilia ry transport is less efficient or in the alveolar region.