Measurement of functional residual capacity through the transient phase of He dilution in newborns

Helium dilution maneuver is used to determine the functional residual capacity (FRC) 14 newborns ages 1-5 mo. The model equation describes the changing alveolar fractions of He and the ventilation promoted by a rebreathing procedure that does not exceed 40 s. The model does not involve the volume of the rebreathing bag usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to newborns. Results show a strong relationship between FRC and the biometrical indexes, and confirm those found in the literature featuring that the measurement duration of FRC can be considerably shortened.