Increased Levels of Outdoor Air Pollutants Are Associated With Reduced Bronchodilation in Children With Asthma

Abstract

Increased outdoor air pollution levels are associated with more frequent use of rescue inhalers in subjects with asthma. However, it is unknown whether this phenomenon is explained by an air pollution-mediated increase in respiratory symptom severity or whether air pollutants decrease the efficacy of short-acting beta-agonists (SABAs). We examined the relationship between the percentage change in FEV(1) after SABA use with outdoor air pollution exposure in 85 children with asthma who were 7 to 12 years of age. Outdoor air pollution exposure was determined by measuring nitrogen dioxide (NO(2)), ozone (O(3)), and fine particulate matter (ie, particulate matter with an aerodynamic diameter < 2.5 microm [PM(2.5)]) levels. These measurements were obtained from the Mexico City Automated Monitoring Network from network sites located within a 5-km radius of each child's home and school. We found that a same-day interquartile increase of 10 parts per billion (ppb) in NO(2) concentration was associated with a reduced response of FEV(1) to SABA therapy (-15%; 95% CI, -29 to -0.5). This association was also significant when considering NO(2) levels in each of the preceding 3 days. An interquartile O(3) increase (16 ppb) in the preceding fifth day was associated with a reduced response to SABA (-11%; 95% CI, -23 to -1); an interquartile PM(2.5) increase (14 microg/m(3)) was not associated with any significant reductions in the response to SABA therapy. These associations were not observed in children receiving therapy with inhaled corticosteroids. Our results suggest that recent exposure to NO(2) and possibly O(3) may reduce the response to SABAs in producing bronchodilation in children with asthma. The association between NO(2) and FEV(1) response to SABA administration may have important implications in understanding how outdoor air pollution levels relate to asthma control.