Diffusional deposition of ultrafine aerosols in a human nasal cast

Abstract

This report describes an experimental study of aerosol deposition in a human nasal cast. A clear polyester resin cast of the upper airways of a normal human adult was used. This life-sized model included nasal hairs, the nasal airways, oral cavity, nasopharynx, larynx and entrance to the trachea. For nasal air flow rates, the measured pressure drop in the cast was similar to the in vivo measurements reported in the literature. Thus, the cast appeared to be a good representation of the nasal airways of living humans. The total deposition was measured in the cast for monodisperse NaCl aerosols between 0.2 and 0.0046 μm at flow rates between 4 and 50 l min −1 of inspiratory flow. The deposition efficiency increased with decreasing particle size and flow rate, indicating that diffusion was the dominant mechanism for deposition. At 20 1 min −1 flow (comparable to that for normal breating at rest), inspiratory deposition efficiencies were 16 and 40% for 0.01 and 0.005 μm particles, respectively. A theoretical equation relating the deposition efficiency to the flow rate and diffusion coefficient was derived based on a turbulent diffusion process. The agreement achieved between the theoretical and measured deposition indicated that the turbulent diffusion was the dominant mechanism of deposition in the nasal cast. This information will be incorporated into future models of respiratory tract dosimetry.