To identify the measurable physiologic changes in the small airways of children with asthma, when employing a 2.5 µm particulate matter (PM2.5) filtration device in their bedrooms.

The population enrolled includes children with mild or moderate asthma who live in a suburb of Shanghai, China, during a low-ozone season. A total of 43 children (5–13 years old; 60% boys) are included in the analysis.

Patients are randomly assigned into either arm of a double-blind crossover study design with 3 consecutive 14 day periods of true filtration-washout-sham filtration or the reverse order. Impulse oscillometry, spirometry, and fractional exhaled nitric oxide (FeNO) were measured before and after each intervention, and peak flow was measured twice per day at home.

PM2.5 concentrations were moderately high (28.6-69.8 $μ$ g/m3) among the enrollees. A decrease in PM2.5 concentration by 63.4% was noted in true filtration bedrooms, when compared with...