Pulmonary Effects of Indoor- and Outdoor-Generated Particles in Children with Asthma

Most particulate matter (PM) health effects studies use outdoor (ambient) PM as a surrogate for personal exposure. However, people spend most of their time indoors exposed to a combination of indoor-generated particles and ambient particles that have infiltrated. Thus, it is important to investigate the differential health effects of indoor- and ambient-generated particles. We combined our recently adapted recursive model and a predictive model for estimating infiltration efficiency to separate personal exposure (E) to PM(2.5) (PM with aerodynamic diameter ≤2.5 μm) into its indoor-generated (E(ig)) and ambient-generated (E(ag)) components for 19 children with asthma. We then compared E(ig) and E(ag) to changes in exhaled nitric oxide (eNO), a marker of airway inflammation. Based on the recursive model with a sample size of eight children, E(ag) was marginally associated with increases in eNO [5.6 ppb per 10-μg/m(3) increase in PM(2.5); 95% confidence interval (CI), −0.6 to 11.9; p = 0.08]. E(ig) was not associated with eNO (−0.19 ppb change per 10μg/m(3)). Our predictive model allowed us to estimate E(ag) and E(ig) for all 19 children. For those combined estimates, only E(ag) was significantly associated with an increase in eNO (E(ag): 5.0 ppb per 10-μg/m(3) increase in PM(2.5;) 95% CI, 0.3 to 9.7; p = 0.04; E(ig): 3.3 ppb per 10-μg/m(3) increase in PM(2.5); 95% CI, −1.1 to 7.7; p = 0.15). Effects were seen only in children who were not using corticosteroid therapy. We conclude that the ambient-generated component of PM(2.5) exposure is consistently associated with increases in eNO and the indoor-generated component is less strongly associated with eNO.