NASAL DEPOSITION OF ULTRAFINE PARTICLES IN HUMAN VOLUNTEERS AND ITS RELATIONSHIP TO AIRWAY GEOMETRY

Very large and very small particles most often deposit in the nasal ai rways. Human volunteers have often been used in deposition studies usi ng particles > 0.5 mu m, whereas physical airway models have been used in studies of ultrafine particle deposition. Studies in airway models provide large data sets with which to evaluate the deposition mechani sm, while in vivo deposition data are needed to validate results obtai ned with nasal models. Four adult male, nonsmoking, healthy human volu nteers (ages 36-57 Fr) participated in this study. Deposition was meas ured in each subject at constant Bow rates of 4, 7.5, 10, and 20 L min (-1). Monodisperse silver particles (5, 8, and 20 nm) and polystyrene latex particles and 100 mn) were used. Each subject held his breath fo r 30-60 sec during which rime, the aerosol was drawn through the nasal airway and exhausted through a mouth tube. Aerosol concentrations in the intake and exhaust air were measured by an ultrafine condensation particle counter. The deposition efficiency in the nasal ah-way was ca lculated taking into account particle losses in the mask, mouth tube, and transport lines. Our results were consistent with the turbulent di ffusional deposition model previously established from studies using n asal airway casts. However, nasal deposition varied widely among the f our subjects. From magnetic resonance imaging data of in vivo nasal ai rway dimensions for the subjects in this study, we calculated the mean cross-sectional area (<(A)over bar (c)>), mean perimeter (<(P)over ba r r>), and total surface area (A(s)) of the individual nasal passages. The turbulent diffusional deposition model was extended to provide a relationship between deposition efficiency and nasal airway dimensions . Our results suggested that deposition can be correlated using the pa rameter of (A(s)/<(A)over bar (c)>)(0.75)(<(P)over bar r>)(0.45). This information indicates a higher nasal deposition for a person with a s maller cross-sectional area, larger surface area, and larger perimeter . This approach has significant potential for future research in the a rea of intersubject variability of aerosol and vapor deposition.