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 β-agonists (SABAs).
We examined the relationship between the percentage change in FEV1 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 (NO2), ozone (O3), and fine particulate matter (ie, particulate matter with an aerodynamic diameter < 2.5 μm [PM2.5]) 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 NO2 concentration was associated with a reduced response of FEV1 to SABA therapy (−15%; 95% CI, −29 to −0.5). This association was also significant when considering NO2 levels in each of the preceding 3 days. An interquartile O3 increase (16 ppb) in the preceding fifth day was associated with a reduced response to SABA (−11%; 95% CI, −23 to −1); an interquartile PM2.5 increase (14 μg/m3) 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 NO2 and possibly O3 may reduce the response to SABAs in producing bronchodilation in children with asthma. The association between NO2 and FEV1 response to SABA administration may have important implications in understanding how outdoor air pollution levels relate to asthma control.