Interspecies Modeling of Inhaled Gases

Abstract

Information concerning factors affecting human Inhalation Toxicology can be obtained from exposure experiments performed with surrogates such as laboratory rats. An interspecies model simulating mass transport processes is in much demand to aid in the interpretation and extrapolation of the resultant data to human conditions. In this work, the mathematical model developed by Martonen et al. (1995) that describes mass transfer efficiencies of inhaled gases (e.g., ozone) in the human respiratory tract has been adapted to (and subsequently verified for) rat airways. The Weibel (1991) and Yeh et al. (1979) morphologies are used to describe the human and rat lungs, respectively. Enhanced CO₂ concentrations in inhalation exposure chambers are used to produce desired breathing patterns in rats that mimic human breathing patterns as functions of increased physical activity levels. Results show that diffusion efficiencies for rats are about 100% higher than for humans in most tracheobronchial airways at corresponding levels of activity. The most suitable approximation of human diffusion efficiency curves at a sedentary condition is attained using a high CO₂ concentration (8%) exposure chamber environment in rat experiments.