Role of labour in the establishment of functional residual capacity at birth.

Intrathoracic pressure and volume changes were measured during the spontaneous first breath in 11 healthy term neonates delivered by emergency caesarean section (CS). Although inspiratory and expiratory rates were higher than those found among babies delivered by elective CS, inspiratory volume was very similar and these babies, unlike those delivered by elective CS, had all formed a functional residual capacity at the end of the first breath. We obtained cord arterial and venous samples for catecholamine analysis concurrently, and found that most of the babies had concentrations of plasma noradrenaline similar to babies delivered by elective CS--high values were found only among infants who had suffered fetal distress. Both catecholamine excretion and method of delivery may be important in the formation of the functional residual capacity at birth.