Nasal Deposition of Ultrafine Particles in Human Volunteers and Its Relationship to Airway Geometry

Abstract

Very large and very small particles most often deposit in the nasal airways. Human volunteers have often been used in deposition studies using particles > 0.5 μm, 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 mechanism, while in vivo deposition data are needed to validate results obtained with nasal models. Four adult male, nonsmoking, healthy human volunteers (ages 36–57 yr) participated in this study. Deposition was measured in each subject at constant flow rates of 4, 7.5, 10, and 20 L min ⁻¹. Monodisperse silver particles (5, 8, and 20 nm) and polystyrene latex particles (50 and 100 nm) were used. Each subject held his breath for 30–60 sec, during which time, 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 airway was calculated taking into account particle losses in the mask, mouth tube, and transport lines. Our results were consistent with the turbulent diffusional deposition model previously established from studies using nasal airway casts. However, nasal deposition varied widely among the four subjects. From magnetic resonance imaging data of in vivo nasal airway dimensions for the subjects in this study, we calculated the mean cross-sectional area ([Abar]_c ), mean perimeter ([Pbar]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 parameter of (A_s/[Abar]_c )⁰⁷⁵([Pbar]r)^0–45. This information indicates a higher nasal deposition for a person with a smaller cross-sectional area, larger surface area, and larger perimeter. This approach has significant potential for future research in the area of intersubject variability of aerosol and vapor deposition.