Effect of exposure to low levels of ozone on the response to inhaled allergen in allergic asthmatic patients.

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 responsiveness.