Nasal molds as predictors of fine and coarse particle deposition in rat nasal airways

Respiratory particle toxicity and accompanying dosimetry are commonly studied in laboratory animals and results are extrapolated to humans. Nasal deposition in the rat has been studied experimentally using acrylic molds made from postmortem casts and in vivo techniques. A previous study (Martonen & Yang, 1993) found agreement between the deposition efficiencies of rat nasal airways and nasal molds for ultrafine particles (<0.1 mu m) but disagreement for particles greater than 1 mu m. In this work, the hypothesis that molds made from postmortem casts of rat nasal airways are suitable predictors of the deposition of particles greater than 1 mu m in live rats was reevaluated by considering data recently obtained in our laboratory. Comparisons of deposition data for steady and pulsatile flows in the inspiratory and expiratory directions from studies using an F344 nasal mold and Long-Evans rats were performed. The validity of comparing nasal deposition data derived from an F344 nasal airway with data from Long-Evans airways was supported by a comparison of the nasal morphologies of these strains. Graphical comparisons of data showed good agreement between deposition in a nasal mold and rat nasal airways for particles with diameters between 0.5 and 4 mu m; statistical comparisons indicated differences. Statistical findings were not considered conclusive because of differences in variability between the studies. The available data suggest that good estimates of total nasal deposition in rats can be obtained by using rat nasal molds as surrogates for their live counterparts in studies of the deposition of particles greater than about 0.5 mu m.