An Empirical Dosimetry Model of Aerodynamic Particle Deposition in the Rat Respiratory Tract

Abstract

The authors thank Jeanne Galbo and Cyndi Saunders for their expert word processing support i n the preparation of this manuscript. The authors would also like to thank the anonymous reviewers for their thoughtful and insightful comments on the submitted manuscript. EMPIRICAL PARTICLE DOSIMETRY IN THE RAT 541Zhang and Yu (1 993) presented empirical equations for nasal fractional deposition in humans and small laboratory animals (mouse, hamster, rat, and guinea pig) using the published data of Raabe and colleagues (1 977, 1988). They did not, however, consider fractional deposition in the tracheobronchial (TB) or alveolar (A) regions of the respiratory tract.All of the empirical models of regional fractional deposition in humans and the ET model of Zhang and Yu (1993) fit independent equations to deposition efficiency (number or mass depositedhumber or mass entering that region) for each region. This approach treats the respiratory tract as a series of linked filters through which the aerosol passes (Rudolf et al., 1983;Heyder & Rudolf, 1977). Asgharian et al. (1995) recently published an empirical model of fractional A deposition in the human, monkey and rat. Their model differs from the other models referenced already in that their equations for the A region are calculated directly from deposition fractions rather than from deposition efficiencies. In contrast to regional deposition efficiencies that depend only on ventilatory parameters, airway geometry, and particle characteristics, regional deposition fractions depend on fractional deposition in preceding regions as well. This limits the usefulness of such a model but does provide a way to use published fractional deposition data in empirical models even when, as i s often the case, the regional efficiencies cannot be derived. In the model of Asgharian et al. (1 995), fourth-order polynomials were essentially eye-fit through published data on A deposition following exposure to monodisperse or near monodisperse particle size distributions. In a technique similar to that used by Kobrich et al. (1994) for humans, Asgharian and co-workers (1 995) then generated equations to estimate A deposition of polydisperse spherical particles by first integrating the monodisperse deposition equation with a lognormal distribution describing the polydisperse particle size distribution. Fourth-order polynomials were then fit to the resulting predicted polydisperse deposition fractions to provide an empirical model for polydisperse particle fractional deposition in the A region. The model of Asgharian and colleagues (1995) does not describe fractional deposition in either the ET or TB regions, although they discuss that the same procedures could be applied to these regions.In this article, we present an empirical model for the rat to calculate predicted fractional deposition of particles in the aerodynamic size range. This model consists of three independent deposition efficiency equations (ET, TB, and A regions). Multiplying predicted deposition efficiencies (or their complemen...

Physiologic Models for Comparison of Inhalation Dose Between Laboratory and Field-Generated Atmospheres of a Dry Powder Fire Suppressant

“…Figure 8, 9, and 10 illustrate the agreement between published data sets and predicted particle deposition in the extrathoracic, tracheobronchial, and pulmonary regions of the lung, respectively. The reconstruction of published data (Raabe et al, 1977(Raabe et al, , 1988Yeh, 1980;Menache et al, 1996) and the repetition of Wojciac's (1988) calculations demonstrate that the modifications made here did not alter the model structure in an unacceptable fashion. For the particle size range depicted, on average, the reported and predicted particle deposition fractions were in agreement by factors of 1.012, 0.9988, and 0.838 for extrathoracic, tracheobronchial, and pulmonary regions, respectively .…”

“…The annotated data point from Schum and Yeh (1980) was computed as 100% minus thoracic deposition. Remaining data are from Yeh (1980), Rabbe et al (1977), Rabbe et al (1988), and Menache et al (1996).…”

“…We have recast this model in ACSL (Advanced Continuous Simulation Language, MGA Corp, Concord, MA), which allows facile integration of time varying systems of differential equations. We provided an extrathoracic deposition compartment by fitting an empirical equation to the data of Menache et al (1996) and redefining input to the Wojciak model. This had the effect of extending the region of particle size model validity to approximately 10 µm.…”

“…Two approaches have been used in describing the fate of inhaled particulate matter: modeling on an empirical compartment basis (Graham et al, 1996;Menache et al, 1996), or modeling on the basis of pulmonary anatomy and the physics of fine particle behavior in flowing air. We have chosen the latter approach.…”

The Relevance of Animal Models for Aerosol Studies

“…Therefore, this inhalability curve strictly applies only to this case. The inhalability of particles in laboratory animals is less well defined, (15,61,62) and is dependent on the specific aerosol exposure system used. Although the curves in Figure 2 are widely used, the variability in aerosol deposition in human subjects is often underappreciated.…”