Regional Deposition of Particles in Human Lung after Induced Bronchoconstriction

Abstract

The percentage 24-hr lung retention (Ret²⁴), a measure of penetration to the aveoli, of 4 μm monodispersed Teflon particles, aerodynamic diameter 6 μm, was studied in 8 healthy nonsmokers. The particles were inhaled at 0.2 1/sec with maximally deep breaths. Bronchoconstriction was induced by inhalation of a methacholine-bromide aerosol for one exposure before and for one exposure after inhalation of the Teflon particles. Airway resistance (R_aw) was measured using a whole body pletys-mograph before and after the induction of bronchoconstriction and increased on an average by a factor 2–3. Ret₂₄ was significantly lower when the Teflon particles were inhaled during bronchoconstriction than when bronchoconstriction was induced after inhalation of the Teflon particles, 26 ± 12% and 48 ± 6% (mean ± SD), respectively. These experimental data agree fairly well with data on deposition due to impaction and sedimentation using a lung model where the diameters of the airways were varied so that an increase in airway resistance occurs similar to that produced in our experimental subjects. However, the experimental data tended to be lower than the theoretical ones when the particles were inhaled during the induced bronchoconstriction. In this study, where the mucociliary transport system was stimulated by metha-cholinebromide, the percentage 3-hr retention (Ret₃) was highly correlated with Ret₂₄, r = 0.97, i.e., Ret₃, can be used instead of the Ret₂₄. This implies that radio-nuclides with shorter half-lives which give lower radiation doses, can be used, and that subjects can be studied within shorter periods of time.