Individual Differences in Regional Deposition of 6-μm Particles in Humans with Induced Bronchoconstriction

Abstract

The effect of induced bronchoconstriction on regional lung deposition of 6 μm 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 25–1 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 (R_aw) 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 R_aw and Ret₆ with a decrease of Ret₆ with increased R_aW This decrease varied markedly among the subjects. The relationship between R_aw 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.