Methacholine Responsiveness Is Not Associated With O3-lnduced Decreases in FEV1

Controlled human exposure studies have suggested that the National Ambient Air Quality Standard for ozone (O3) may not provide a margin of safety to protect the most susceptible members of the population from adverse health effects. Although the subgroups of the population that are most susceptible to O3have not been identified, recent work in our laboratory suggested that methacholine responsiveness might be an important determinant of susceptibility to O3. Patients and methods: To test the hypothesis that methacholine responsiveness is correlated with FEV1response after O3exposure, we conducted methacholine challenge tests and O3(0.20 ppm) and filtered air exposures for 4 h with moderate exercise on 66 healthy individuals.