Participant recruitment and characterization
AIRWEIGHS is a single-center, randomized, parallel-assignment, quadruple-masked clinical trial of an air purifier intervention for obesity-associated asthma (NCT02763917). The study was approved by the IRB-1 Committee of the institutional review board of Johns Hopkins University School of Medicine (IRB00074171). All participants gave assent, and all primary caretakers gave written informed consent.
Participants were recruited from patients seen at the Johns Hopkins outpatient clinics and the pediatric emergency department, community engagement activities, recruitment flyers posted in public locations and a registry of previous study participants. Eligible participants were aged 8–17 years, nonsmokers, and had physician-diagnosed asthma by National Asthma Education and Prevention Program (NAEPP) criteria with at least one exacerbation in the prior year11. Those who had other significant cardiopulmonary disease were excluded. A diagram of the participant flow is shown in Figure 1 .
Sociodemographic information was obtained by participant or caregiver report. Body weight and height were measured in triplicate and each averaged, from which body mass index (BMI) was calculated and converted to a normalized z-score based on the 2000 Centers for Disease Control and Prevention (CDC) growth charts12,13.