Prolongation of inspiration during lower airway occlusion in children.

Inspiration is strongly inhibited by volume-related vagal afferents in human neonates and animals, but this reflex is not as active in human adults during normal breathing. To determine whether volume-related inspiratory inhibition occurs beyond the neonatal period, we performed 10 +/- 1 end-expiratory occlusions in nine asleep children, ages 2-29 mo, with cuffed tracheostomy or endotracheal tubes in place. Airflow, tidal volume, occlusion pressure, and surface diaphragm electromyogram (DIA EMG) were simultaneously recorded. Occlusion consistently increased mechanical (P less than 0.002) and neural inspiratory times (P less than 0.001). During occluded respiratory efforts, peak amplitude of DIA EMG increased by 22 +/- 10% (P less than 0.002). In contrast, initial rate of rise of DIA EMG did not change. We conclude that in children with isolated lower airways, end-expiratory occlusions prolonged inspiratory duration as measured by both mechanical and neural parameters. The lack of an associated increase in rate of rise of DIA EMG strongly suggests that inspiration is prolonged by release of volume-related inhibition of inspiration rather than by facilitation. These data provide evidence for the presence of the Hering-Breuer reflex beyond the neonatal period.