Deposition of inhaled particles in the mouth and throat of asthmatic subjects

We previously studied the deposition of inhaled particles in the mouth and throat of asthmatic patients, and found large, reproducible differences among subjects. In the present study, we examined whether anatomical and/or functional differences in the pharynx and larynx could underlie this interindividual variation. Deposition in the mouth and throat, and in the lung was estimated in 16 asthmatic subjects after inhalation of 3.6 microns (aerodynamic diameter) monodisperse Teflon particles labelled with 111In. The particles were inhaled at a flow rate of 0.5 l.s-1 with maximally deep breaths. Radioactivity was measured by external scanning over head and neck, lungs and stomach, immediately after the inhalation. Radioactivity in the lungs was also measured 24 h later. A measure of the total amount of particles deposited in the mouth and throat was obtained from the added activities in mouthwash, head and neck, and stomach, immediately after the inhalation of the test particles. Pharynx and larynx function was examined by fibreoptic laryngoscopy performed during a corresponding inhalation procedure. Deposition in the mouth and throat varied widely among the subjects, ranging 9-76% (median 12%). We found two subpopulations, 13 subjects in the range 9-34%, and 3 subjects with > 70% deposition. Deviations in pharyngeal configuration during inhalation were significantly related to high mouth and throat deposition, whereas functional differences in the larynx were not. Our study shows that mouth and throat deposition may be extremely high in some asthmatics, and that pharyngeal configuration affects deposition of particles in the mouth and throat.