REFERENCING LUNG-VOLUME FOR MEASUREMENTS OF RESPIRATORY SYSTEM COMPLIANCE IN INFANTS

We propose a method for measurements of respiratory system compliance (C(rs)) in spontaneously breathing infants, which circumvents the pote ntial problems introduced by the breath-by-breath oscillations in the end-expiratory level, i.e., functional respiratory capacity (FRC). Cha nges in lung volume (V) and pressure at the airway opening (P(ao)) wer e measured in 10 infants breathing through a face mask. A first brief occlusion was to establish a reference V and the corresponding static P(ao); a second occlusion was done at a different V, within the same e xpiration, or in the following breath. Both occlusions were sufficient ly long for the establishment of a stable P(ao) value. From the V diff erence (deltaV, where deltaV was at least 20% tidal volume) and the co rresponding difference in P(ao) (deltaP(ao)) Cr(rs) was computed and a veraged (C(rs)[REF.VOL.] = deltaV/deltaP(ao)). Although, on average, t he results were similar to those obtained by the traditional multiple occlusions technique with linear regression analysis of the P(ao)-V da ta points (C(rs)[MOT]), in several infants C(rs)[REF.VoL.] tended to b e slightly higher than C(rs)[MOT]. Some possibilities for this discrep ancy are discussed. It seems likely that breath-to-breath oscillation in FRC may potentially lower C(rs)[MOT] by introducing a bias on the V measurement at low P(ao). We conclude that referencing V for C(rs) me asurements in spontaneously breathing infants is a simple approach, wh ich does not require linear regression analysis and circumvents the ef fects of oscillation in FRC. (C) 1993 Wiley-Liss, Inc.