ANALYSIS OF FORCED EXPIRATORY MANEUVERS FROM RAISED LUNG-VOLUMES IN PRETERM INFANTS

During recent years it has been suggested that forced expiratory measu rements, derived from a lung volume set by a standardized inflation pr essure, are more reproducible than those attained during tidal breathi ng when the rapid thoracoabdominal compression technique is used in in fants. The aim of this study was to evaluate the feasibility of obtain ing measurements from raised lung volumes in unsedated preterm infants . Measurements were made in 18 infants (gestational age 26-35 wk, post natal age 1-10 wk, test weight 1.4-3.5 kg). Several inflations [1.5-2. 5 kPa (15-25 cmH(2)O)] were used to briefly inhibit respiratory effort before the rapid thoracoabdominal compression was performed. Conventi onal analysis of flows and volumes at fixed times and percentages of t he forced expiration resulted in a relatively high variability in this population. However, by using the elastic equilibrium point (i.e., th e passively determined lung volume, derived from passive expirations b efore the forced expiration) as a volume landmark, it was feasible to achieve reproducible results in unsedated preterm infants, despite the ir strong respiratory reflexes and rapid respiratory rates. Because th is approach is independent of changes in expiratory time, expired volu me, or applied pressures, it may facilitate investigation of the effec ts of growth, development, and disease on airway function in infants, particularly during the first weeks of life, when conventional analysi s of forced expirations may be inappropriate.