Partial expiratory flow-volume curves in young children.

The purpose of this study was to examine the variability and possible uses of partial maximal expiratory flow-volume curves as a measurement of lung function in young children. Repeated partial flow-volume curves followed by measurement of resting lung volume were obtained from 45 healthy children and 12 with generally mild lung disease caused by cystic fibrosis; the age range was 3 to 6 yr. At each test session, each child completed 3 runs; for each run, values of functional residual capacity, maximal flow at functional residual capacity, and maximal flow compensated for lung size were obtained. Within-subject, day-to-day, and among-subject variabilities in the healthy group were very close to those reported for similar flow rates and lung volume in older subjects who are able to produce a full forced vital capacity. When compensated for lung volume, healthy boys had significantly lower flow rates than did girls. Test sensitivity and specificity were such that the cystic fibrosis and healthy groups were easily discernible. Among-subject variability of flow rates in healthy children was large enough to make the accurate detection of mild airways dysfunction in any given individual difficult.