The effect of exposure to ozone and nitrogen dioxide on the airway response of atopic asthmatics to inhaled allergen - Dose- and time-dependent effects

Eleven mild atopic asthmatic patients were exposed for 6 h, in randomized o rder, to air, 100 ppb O-3, 200 ppb NO2, and 100 ppb O-3 + 200 ppb NO2, foll owed immediately by bronchial allergen challenge. Subsequently 10 of these patients were exposed for 3 h to air, 200 ppb O-3, 400 ppb NO2, and 200 ppb O-3 + 400 ppb NO2, followed immediately by bronchial allergen challenge. A ll exposures were carried out in an environmental chamber, with intermitten t moderate exercise, and a minimal interval of 2 wk. Exposure for 6 h to 10 0 ppb O-3, 200 ppb NO2, and 100 ppb O-3 + 200 ppb NO2 did not lead to any s ignificant increase in the airway response of these individuals to inhaled allergen, when compared with exposure for 6 h to air. In contrast, exposure for 3 h to 200 ppb O-3, 400 ppb NO2, and 200 ppb O-3 + 400 ppb NO2 signifi cantly decreased the dose of allergen tin log cumulative breath units [CBU] ) required to decrease FEV1 by 20% (allergen PD20FEV1), compared with expos ure to air (geometric mean CBU: 3.0 for air versus 2.66 for O-3 [P = 0.002] ; 2.78 for NO2 [p = 0.018]; 2.65 for O-3 + NO2 [p = 0.002]). These results suggest that the pollutant-induced changes in airway response of mild atopi c asthmatics to allergen may be dependent on a threshold concentration rath er than the total amount of pollutant inhaled over a period of time.