The study was approved by the University of Toronto Human Ethics Committee; informed written consent was obtained from all subjects. We studied 15 never smoker asthmatics (7 male and 8 female) with a mean (±SD) age of 25.6 ±6.76 years. Asthma was defined by the American Thoracic Society criteria.15 Subjects with a baseline FEVi >70 percent predicted and who had exhibited a fall in FEVi >15 percent after exercise were included in the study. None had any symptoms of acute respiratory tract illness within the 6 weeks preceding the study. They refrained from taking their bronchodilator medications for at least 12 h prior to testing, and theophylline and antihistamines for 48 h. None had required parenteral or oral corticosteroids in the previous year.
This was a double-blind, placebo-controlled study performed during the winter months. Subjects came to the laboratory at the same time of day on 3 separate days, at least 1 week apart. Patients were studied only if FEVi was within 10% of the baseline measured on the screening day. inhalers for asthma
After an initial screening day (day 1) to determine baseline FEVi and exercise response, subjects were randomized to receive either ozone or air (placebo) during a 1-h period before performing the exercise challenge on days 2 and 3. Environmental levels of ozone were obtained from an analyzer (Bendix) for indoor readings and from the Ontario Government Air Resources Branch for outdoor values.
The exercise protocol consisted of 6 min of treadmill exercise under constant environmental conditions: temperature 23°C (± 1) and relative humidity 50% (±5). Exercise challenges were performed at the same time of the day and treadmill speed and inclination were such that patients achieved their maximal exercise. Exercise was terminated if the subject no longer wished to continue due to shortness of breath or fatigue.