SMOKING CESSATION AND ACUTE AIRWAY RESPONSE TO OZONE

Pulmonary function and symptom responses of asymptomatic smokers were measured during chamber exposures to ozone or filtered air. Subjects were evaluated while habituated to smoking and after 6 mo of smoking abstinence. At the onset of treatment, subjects (n = 18) who had a history of smoking 33.4 +/- 15.6 packs/y and who had almost normal pulmonary function (forced vital capacity [FVC], forced expiratory volume in 1 s [FEV1.0], and mid-maximal flow [MMF] were > 82% of predicted) were unresponsive to ozone exposure (0.4 ppm for 2 h). A matched group of control smokers (n = 16) did not respond to filtered air exposure. After 6 mo of smoking cessation, baseline MMF rates improved significantly (p < .02); ex-smokers (n = 15) raised this index from 3.32 to 4.11 l/s. All 9 subjects who abstained from smoking cigarettes for 6 mo and who were re-exposed to 0.4 ppm ozone had significant (p < .01) reductions in MMF (from a mean of 3.86 +/- 1.32 [standard deviation] to 2.99 +/- 0.94 l/s, i.e., 22.5% reduction) and marginally significant reductions in comfort, as evidenced by an increase in the incidence of dry cough (p < .10). The FVC was not reduced during ozone exposure. Control ex-smokers (n = 6) remained unresponsive to filtered air exposure. The ex-smokers' responses to ozone and their improved MMF during the period of smoking abstinence were correlated (coefficient = .88), i.e., subjects with the largest baseline gains in MMF after withdrawal experienced the largest acute decrements in MMF during ozone exposure. This study suggests that functional response and symptom sensitivity to ozone are moderated or nonexistent in asymptomatic smokers; after 6 mo of smoking cessation and improvement in lung function, airway response and subjective awareness to ozone emerge. However, the reduction in FVC, which is a common response of nonsmokers to ozone exposure, was not restored by 6 mo of abstaining from smoking.