Individual differences in regional deposition of 6-micron particles in humans with induced bronchoconstriction

The effect of induced bronchoconstriction on regional lung deposition of 6 microns aerodynamic diameter 99mTc-labeled Teflon particles was studied in eight healthy non-smokers. The Teflon particles were inhaled at 0.5 l/s from a 25-l glass bulb with 8-12 maximally deep breaths on four consecutive days. For three exposures, various degrees of bronchoconstriction were induced using an aerosol of methacholine bromide before the inhalation of the Teflon particles. For the fourth (control) exposure, bronchoconstriction was induced after the inhalation of the Teflon particles. The degree of bronchoconstriction was quantified by measurements of airway resistance (Raw) using a whole-body plethysmograph. The fraction of alveolarly deposited particles in the lung (FAD) was estimated by measurements of radioactivity in the lung immediately after inhalation of the Teflon particles and 6 h later. Earlier studies have shown that when the mucociliary transport is stimulated with the cholinergic aerosol used in this study, the 6-h retention values (Ret6) are similar to the 24-h values. Within the subjects there was a close relationship between Raw and Ret6 with a decrease of Ret6 with increased Raw. This decrease varied markedly among the subjects. The relationship between Raw and Ret6 calculated from the model by the Task Group on Lung Dynamics, in which the airway diameters were varied, agreed with our experimental data. On an average, airway resistance of 1 and 2 cm H2O.s/l correspond to FAD of about 50% and 25%, respectively.