The effect of acute outdoor air pollution on peak expiratory flow in individuals with asthma: A systematic review and meta-analysis.

Abstract Objectives Acute exposures to outdoor air pollution have been shown to reduce lung function in children with asthma, but the effect on adults with asthma has not been established in a meta-analysis. The objective of this study was to conduct a systematic literature review and meta-analysis of studies that assessed the relationship of outdoor air pollution and peak expiratory flow (PEF) in adults with asthma. Methods Studies that contained data on outdoor air pollution levels (PM10, PM2.5, or NO2) and PEF in adults with asthma were eligible for inclusion. Effect estimates were quantified for each air pollution measure using random effects models. Heterogeneity was investigated with the Q-test and I2 statistics. Meta-regression and subgroup analyses were conducted to determine differences in effect by air pollution measures and the inclusion of smokers. Results A total of 22 effect estimates from 15 studies were included in this review. A 10 μg/m3 increase in acute PM10 exposure was associated with a -0.19 L/min (95% CI: -0.30, -0.09) change in PEF. For both PM10 and PM2.5, the inclusion of current smokers was a significant source of heterogeneity among studies (meta-regression: p=0.04 and p=0.03). Among studies that only included non-smokers, a 10 μg/m3 increase in acute exposure to PM10 and PM2.5 was associated with changes in PEF of -0.25 L/min (95% CI: -0.38, -0.13) and -1.02 L/min (95% CI: -1.79, -0.24), respectively. Conclusions This study provides evidence that acute increases in PM10 and PM2.5 levels are associated with decreases in PEF in adults with asthma, particularly among non-smokers.