Study objectives: In a previous study published by our group, six out of nine subjects with mild allergic asthma were shown to have an enhanced response to allergen challenge following a 1-h exposure in an 0.8-m3 exposure chamber (modified from a body plethysmograph) to an average of 120 parts per billion (ppb) ozone at rest. Other studies failed to confirm this effect. In the present study, using a similar design, we reexamined this effect using a larger group of asthmatics and a larger chamber allowing minimal fluctuations in ozone levels during exposures.
Design: Prospective, randomized single-blinded crossover study.
Setting: Pulmonary function laboratory equipped with an exposure chamber.
Subjects: Fifteen subjects had mild allergic asthma; 9 men and 6 women; the mean (SD) age was 32.5 (10) years; FEV1 was 3.4 (0.8) L; baseline methacholine provocation concentration causing a 20% fall in FEV1 was (PC20) 3.28 (4.1) mg/mL.
Interventions: Each participant was exposed, at rest, on 1 day to filtered air and on another day to ozone (mean level=120 ppb) in a larger exposure chamber than the one used in our first study with less variability in ozone level (110 to 130 vs 85 to 175 ppb) using a random, single-blinded design. After each exposure, the subject was challenged with allergen (nine with grass pollen extract and six with ragweed extract) and allergen PC15 was measured.
Results: Ozone preexposure did not affect allergen PC15 when compared with clean air preexposure (allergen PC15 dilution 1/114 vs 1/119, respectively). Ozone vs air preexposure resulted in an allergen PC15 that was lower in five subjects, higher in six, and unchanged (within one doubling dose) in four.
Conclusions: At this low level with less variability and lower peaks than our previous study, ozone had no significant effect on airway allergen responsivess.