PROPORTION OF MODERATELY EXERCISING INDIVIDUALS RESPONDING TO LOW-LEVEL, MULTI-HOUR OZONE EXPOSURE

The purpose of this study was to describe the proportion of moderately exercising individuals experiencing significant respiratory responses to low-level, multi-hour ozone exposure as a function of ozone concen tration and exposure duration. Sixty-eight healthy, nonsmoking adults, ages 18 to 34 yr, underwent two or more 6.6-h exposures to 0.0, 0.08, 0.10, or 0.12 ppm ozone. Five hours of exercise was performed during exposure, and lung function was measured before exposure and following each hour of exposure. For each combination of concentration and dura tion, each individual was determined to either have or not have experi enced a 10% or greater decrement in FEV(1). A logistic function was us ed to model the proportion of individuals experiencing such a decremen t as a function of concentration and exposure duration. Bootstrap 90% confidence intervals (Cls) were calculated around the predictions. The model was found to give predictions that were in good agreement with observed data. The lowest level of exposure (C x T) for which the 90% Cl excluded zero was approximately 0.2 ppm-h. For exposu re to 0.12 pp m ozone for 6.6 h, 47% (90% Cl = 30 to 65%) of exposed individuals wer e predicted to experience a 10% decrement in FEV(1). A greater proport ion of younger adults than of older adults were found to experience a given effect for a given exposure.