INTERSPECIES MODELING OF INHALED GASES

Information concerning factors affecting human inhalation toxicology c an be obtained from exposure experiments performed with surrogates suc h as laboratory rats. An interspecies model simulating mass transport processes is in much demand to aid in the interpretation and extrapola tion of the resultant data to human conditions. In this work, the math ematical model developed by Martonen et al. (1995) that describes mass transfer efficiencies of inhaled gases (e.g., ozone) in the human res piratory tract has been adapted to (and subsequently verified for) rat airways. The Weibel (1991) and Yeh et al. (1979) morphologies are use d to describe the human and rat lungs, respectively. Enhanced CO2 conc entrations in inhalation exposure chambers are used to produce desired breathing patterns in rats that mimic human breathing patterns as fun ctions of increased physical activity levels. Results show that diffus ion efficiencies for rats are about 100% higher than for humans in mos t tracheobronchial airways at corresponding levels of activity. The mo st suitable approximation of human diffusion efficiency curves at a se dentary condition is attained using a high CO2 concentration (8%) expo sure chamber environment in rat experiments.