Predicted Nasal and Tracheobronchial Particle Deposition Efficiencies for the Mouse

Abstract

ii) An11. 0<<'11p. HJy .• Vol. 38. Supplemcn1 I. pp. JJ S-141 . 1994 El ~'· ier Science Ltd Copyrigh1 i ' 1994 British <Xcupa1iona l Hygiene Sociely Printed in Great Britain. All rights reserved 0003-4878/ 94 S7.00 + 0.00 /11/Jaled Particles VII Pergamon PREDICTED NASAL AND TRACHEOBRONCHIAL PARTICLE DEPOSITION EFFICIENCIES FOR THE MOUSE* M. J. OLDHAM, R. F . PHALEN, G. M. SCHUM and D. s. DANIELS Department of Community and Environmental Medicine, University of California, Irvine, CA 92717, U .S.A. Abstract-Few models are available for predicting the efficiency of deposition of-inhaled particles in the various regions of the respiratory tract of the mouse. The purpose of this study was to improve the ability to predict upper airway (nose, pharynx and larynx) and tracheobronchial deposition efficiencies for inhaled aerosols in the laboratory mouse. Currently-used equations for predicting nasal deposition efficiencies in humans are semi-empirical and utilize airflow and/or pressure drop data. Therefore, we measured nasal pressure drop and airflow in anaesthetized mice and used this information, together with published data , to formulate aerosol deposition equations. Tracheobron- chial deposition efficiency is usually predicted by considering three mechanisms (impaction, sedimentation and diffus ion ), along with airway anatomical and airflow information. A typical path tracheobronchial airway geometry, complete to the terminal bronchiole, was developed for the mouse from detailed measurements of three replica respiratory tract casts. Particle deposition efficiency calculations were then performed for the tracheobronchial region of the adult mouse a nd compared with published estimates of aerosol deposition in mice. The calculations, which covered a particle diameter range of 0.1- 100 11m (aerodynamic), tended to underestimate the experimental measure- ments in mice. The calculations did not take into account deposition during exhalation, or the effects of several other complex factors. INTRODUCTION BECAUSE the laboratory mouse has been used extensively to study the effects of inhaled substances, the methods of performing inhalation studies are well developed, and a large database on biological effects under a wide variety of conditions exists, it is important to understand the relationship between exposure dose and target tissue dose. However, mathematical equations that use exposure aerosol characteristics in order to predict doses delivered to specific target tissues are not available. Predicted particle deposition efficiency calculations in the mouse have been constrained by the lack of reliable information on upper airways and on the structure of the tracheobronchial tree. We addressed this problem by making upper airway pressure drop vs. airflow measurements and by performing measurements of tracheobronchial airway dimensions for B6C3F 1 mice. The measured resting pressure drop was used .with experimental data from RAABE et al. (1988) to propose upper respiratory tract deposition efficiency equations. The measured geometry was input into a computer program that used particle deposition equations and airflow rates to obtain calculated particle deposition efficiencies. Nasal deposition efficiency (N,rr) has been predicted for humans by an equation of the form: *This paper was included in Poster Session 2 and the discussion included in the summary presented in Section 12.