Study measures and procedures
Children wore a pedometer for one week, then came into the hospital for a study visit to complete a questionnaire, pulmonary MRI, and pulmonary function testing (PFT) on a single day.
Pedometer: Participants were sent a StepsCount Piezo Rx pedometer in the mail to wear at their waist for 7 consecutive days, including 2 weekend days. The pedometer collected daily step count (steps per day) as well as moderate-to-vigorous physical activity (MVPA) data, which is the duration of time (in hours) spent in moderate (100 steps per minute) or vigorous (120 steps per minute) activity14. This pedometer has been validated14, and pedometer data has been shown to be a valid assessment of physical activity in school-aged children15-18. The pedometer was returned to the study team on the day of their study visit. Data was considered valid if a participant had at least 4 valid days (including one weekend day) of data.
Physical Activity Questionnaire (PAQ): The PAQ is a validated, self-report, recall questionnaire which documents the physical activity performed by a child in the most recent 7 days19. The outcome of interest was the PAQ global score, which is a composite score averaging the participation in several different activities to provide an indication of the degree of physical activity performed. A score of 1 indicates low physical activity, while a score of 5 indicates high physical activity19.
Pulmonary MRI: Participants underwent a lung MRI to assess for average total proton density (at a lung volume of functional residual capacity plus one litre), which is a marker of lung tissue inhomogeneity, and average proton density at full expiration, which is an exploratory surrogate measure of gas trapping13,20. Novel research has identified correlations between pulmonary function and proton density,21-23 but MRI measures provide different information about lung architecture13.
Pulmonary function test: PFT included spirometry, which was conducted according to American Thoracic Society protocols24. Measurements included percent-predicted forced expiratory volume in one second (FEV1), forced vital capacity (FVC), forced expiratory flow at 25 and 75% of the pulmonary volume (FEF25-75), residual volume (RV), and lung clearance index (LCI) using Global Lung Function Initiative (GLI) norms25.
Medical chart review: Throughout the course of the study, a research coordinator collected medical history, including maternal and neonatal history, and medications.