Is air trapping important in the maintenance of the functional residual capacity in the hours after birth?

Serial measurements of thoracic gas volume revealed no evidence of air trapping in maintenance of functional residual capacity (FRC) in healthy term babies in the first days of life. Tidal pressue/volume and flow/volume analysis demonstrated intermittent air trapping in only 2 of 19 such babies. Artificial FRC reduction by continuous positive external pressure of 7 cm H20 induced grunting in 4 babies, but otherwise had no effect on spontaneous breathing pattern or on dynamic compliance. Group mean total pulmonary resistance rose by 52.9% but only one baby demonstrated evidence of air trapping. Our findings suggest that FRC is maintained in the immediate neonatal period by some means other than air trapping.