OZONE UPTAKE IN HEALTHY ADULT MALES DURING QUIET BREATHING

Experimental measurements of ozone (O-3) uptake are needed for validat ion of dosimetry model parameters and in predictions as well as for de termining factors affecting uptake and for making comparisons between subpopulations or across species, In this study, 10 healthy adult male subjects were exposed to 0.3 ppm O-3 while seated and breathing natur ally through the nose or mouth, Total respiratory tract O-3 uptake, sp ontaneous breathing parameters, and respiratory gas exchange were meas ured for 10 min under steady-state conditions. The exposure protocol w as replicated in each subject approximately 2 weeks after the first vi sit, On each visit, health exams were performed and spirometric lung m easurements were obtained. The experimental design provided comparison s of total O-3 uptake during nasal and oral breathing, differences in uptake in an individual at two time points, and an examination of betw een-subject variability in O-3 uptake. Exposure to O-3 had no effect o n the breathing parameters or gas exchange, Oral and nasal breathing f requency averaged 16.2 +/- 1.1 (SE) and 16.0 +/- 1.2 breaths per minut e with tidal volumes averaging 651 +/- 46 and 669 +/- 67 ml, respectiv ely, A significant correlation (p < 0.01) was found for the minute vol ume during resting breathing with the percentage of uptake. The percen tage of O-3 uptake was consistently higher (p = 0.02) during oral brea thing (76.5% +/- 3.3) than during nasal breathing (73.1% +/- 3.0) alth ough this difference may not be biologically significant. The variabil ity in percentage of uptake between subjects was substantial with calc ulated uptakes ranging from 51 to 96%, a difference of about 45%. Vari ability in percentage of uptake for an individual was less with the ma ximal difference between the first and second visits being about 20%; the average difference, however, was only about 3%, We conclude that t otal percentage of O-3 uptake is approximately 75% in adult males duri ng resting breathing. It is slightly greater during oral than during n asal breathing, will vary considerably among subjects, and is moderate ly reproducible within a subject. (C) 1996 Society of Toxicology