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 (L) to PM2.5 (PM with aerodynamic diameter <= 2.5 pm) 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-mu g/m(3) increase in PM2.5; 95% confidence interval (CI), -0.6 to 11.9; p = 0.08]. E-ig was not associated with eNO (-0.19 ppb change per 10 mu g/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-mu g/m(3) increase in PM2.5; 95% CI, 0.3 to 9.7; p = 0.04; E-ig: 3.3 ppb per 10-mu g/m(3) increase in PM2.5; 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 PM2.5 exposure is consistently associated with increases in eNO, and the indoor-generated component is less strongly associated with eNO.