METHACHOLINE RESPONSIVENESS IS NOT ASSOCIATED WITH O-3-INDUCED DECREASES IN FEV(1)

Study objective: Controlled human exposure studies have suggested that the National Ambient Air Quality Standard for ozone (O-3) 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 O-3 have not been identified, recent work in our laboratory suggested that methacholine responsiveness might be an important determinant of susceptibility to O-3. Patients and methods: To test the hypothesis that methacholine responsiveness is correlated with FEV(1) response after O-3 exposure, we conducted methacholine challenge tests and O-3 (0.20 ppm) and filtered air exposures for 4 h with moderate exercise on 66 healthy individuals. Results: Repeated measures analysis of variance demonstrated significant changes in FEV(1) (-0.82 +/- 0.63 L), FVC (-0.69 +/- 0.48 L), and specific airway resistance (SRaw) (+1.5 +/- 1.1 L X cm H2O/L/s) across the O-3 exposure that persisted after adjusting for responses to air. Baseline PC100 (the concentration of methacholine that caused a doubling of the baseline SRaw) was weakly associated with O-3-induced increases in SRaw (F-1.54 = 2.85, p = 0.09), but not O-3-induced declines in FEV(1) or FVC. There was a weak association (r = -0.29) between Os-induced responses for SRaw and FEV(1). The FEV(1) responses for O-3 were weakly associated with the symptoms of cough (r = -0.37), wheeze (r = -0.29), chest pain on deep inspiration (r = -0.31), and shortness of breath (r = -0.3), but not with chest discomfort or sputum production. Conclusions: Although we were unable to find support for our hypothesis, we found, somewhat surprisingly, that respiratory symptoms were weakly associated or unassociated with FEV(1) responses after O-3 exposure. This finding implies that individuals may experience adverse effects, ie, respiratory symptoms, without large declines in lung function. Conversely, individuals may suffer large declines in lung function without prominent symptoms and, therefore, may remain in an unhealthy environment despite evidence of toxicity.