B. Webb et al., VAGALLY MEDIATED VOLUME-DEPENDENT MODULATION OF INSPIRATORY DURATION IN THE NEONATAL LAMB, Journal of applied physiology, 76(1), 1994, pp. 397-402
Inspiratory mechanical loads elicit a reflex volume-timing response in
human infants and experimental animals. In adult animals, this reflex
has been shown to be mediated by vagal afferents. It was hypothesized
that the volume-related regulation of inspiratory duration would also
be vagally mediated in the newborn. Single-breath graded inspiratory
loads were presented to 4-day-old anesthetized neonatal lambs breathin
g through a facemask, after tracheostomy, and after bilateral cervical
vagotomy. Inspired volume decreased and inspiratory duration (TI) inc
reased with increasing load magnitude. The increase in TI was greater
with facemask loads than with loads presented after tracheostomy for e
quivalent changes in inspired volume. The volume-related prolongation
of TI after tracheostomy was abolished after cervical bilateral vagato
my. The results demonstrate that the volume-timing reflex in neonatal
lambs after tracheostomy is mediated by vagal afferents. However, in t
he intact lamb, there is also a significant contribution to this refle
x by upper airway afferents.