Am. J. Respir. Crit. Care Med., Vol 152, No. 2, 08 1995, 589-596.
Proportion of moderately exercising individuals responding to low- level, multi-hour ozone exposure
WF McDonnell, PW Stewart, S Andreoni and MV Smith
Clinical Research Branch, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
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 concentration
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 duration, each individual was
determined to either have or not have experienced a 10% or greater
decrement in FEV1. A logistic function was used to model the proportion of
individuals experiencing such a decrement as a function of concentration
and exposure duration. Bootstrap 90% confidence intervals (CIs) 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% CI excluded zero was approximately 0.2
ppm-h. For exposure to 0.12 ppm ozone for 6.6 h, 47% (90% CI = 30 to 65%)
of exposed individuals were predicted to experience a 10% decrement in
FEV1. A greater proportion of younger adults than of older adults were
found to experience a given effect for a given exposure.
