Background: Clinical and epidemiologic studies suggest that ambient ozone exposure may increase the response of patients with asthma to inhaled allergen.
Objectives: The study was designed to evaluate whether a resting 1-hour exposure to 0.12 ppm ozone increases the sensitivity of patients with atopic asthma to inhaled allergen.
Methods: Outside of their allergen season, 15 patients with mild atopic asthma (5 women and 10 men) were exposed, on separate occasions, for 1 hour at rest to clean air and 0.12 ppm ozone. Exposures were separated by a minimum of 4 weeks in a counterbalanced, double-blind design. After exposure, subjects underwent inhalation challenge with doubling doses of aerosolized allergen (0.05 to a maximum of 1600 protein nitrogen units/ml) until we elicited a 20% FEV1 decrement (PC20).
Results: Baseline symptoms, spirometry, and histamine bronchoreactivity were similar for the two exposures. Neither spirometry results nor symptoms were significantly changed after either exposure. The mean difference in response to allergen challenge on the air and ozone days, for the 12 subjects who attained a PC20 was not significant (p = 0.124). Three subjects required the same allergen dose to reach PC20 for both exposures, five required less allergen after ozone exposure, and four required more. There was no order effect for the acute response to allergen challenges (p = 0.325). However, 20 hours after allergen challenge, histamine bronchoreactivity was increased (p < 0.05) to a similar degree for both air and ozone.
Conclusions: A resting exposure for 1 hour to 0.12 ppm ozone did not potentiate an immediate bronchoconstrictive response to grass allergen in this group of patients with mild atopic asthma.