Analysis of forced expiratory maneuvers from raised lung volumes in preterm infants

During recent yearsit has been suggested that forced expiratory measurements, derived froma lung volume set by a standardized inflation pressure, are morereproducible than those attained during tidal breathing when the rapidthoracoabdominal compression technique is used in infants. The aim ofthis study was to evaluate the feasibility of obtaining measurementsfrom raised lung volumes in unsedated preterm infants. Measurementswere made in 18 infants (gestational age 26-35 wk, postnatal age1-10 wk, test weight 1.4-3.5 kg). Several inflations[1.5-2.5 kPa (15-25cmH₂O)] were used to brieflyinhibit respiratory effort before the rapid thoracoabdominal compression was performed. Conventional analysis of flows and volumesat fixed times and percentages of the forced expiration resulted in arelatively high variability in this population. However, by using theelastic equilibrium point (i.e., the passively determined lung volume,derived from passive expirations before the forced expiration) as avolume landmark, it was feasible to achieve reproducible results inunsedated preterm infants, despite their strong respiratory reflexesand rapid respiratory rates. Because this approach is independent ofchanges in expiratory time, expired volume, or applied pressures, itmay facilitate investigation of the effects of growth, development, anddisease on airway function in infants, particularly during the firstweeks of life, when conventional analysis of forced expirations may be inappropriate.