Duration of pulmonary function adaptation to ozone in humans

The duration of pulmonary function adaptation subsequent to cessation of a 5-day repeated ozone (O3) exposure was studied in 24 nonsmoking human subjects. A three-week, 3 hr/day study was conducted. The subjects received filtered air on Week 1 and 0.4 ppm O3 on Week 2. During Week 3, 13 subjects were re-exposed to O3 on Friday and 11 were re-exposed to O3 on Tuesday. Spirometric measurements (FVC and FEV1) and bronchial reactivity to methacholine showed adaptation within 2-3 days of the repeated daily exposures (Week 2). Although the duration of adaptation seen with bronchial reactivity appears longer than 7-days, the FVC and FEV1 clearly demonstrated complete loss of adaptation by 7 days, with a trend toward significance by 4 days. We conclude, therefore, the loss of ozone adaptation in pulmonary function is a gradual phenomenon lasting less than 7 days following cessation of repeated daily exposures.