The present study was aimed at investigating the principal reflex mechanism by
which non-nutritive swallowing (NNS) is inhibited by application of a nasal CPAP 6
cm H2O during quiet sleep (QS) in newborn lambs. Eighteen full-term lambs were
chronically instrumented and evenly distributed into 3 separate groups to sort out
whether reflex activity originates from the upper or lower airway receptors. Six lambs
were tracheotomized, six other lambs underwent a 2-step bilateral intrathoracic
vagotomy while the remaining 6 lambs underwent chronic laryngo-tracheal
separation (isolated upper airway group). Forty-eight hours after surgery, each nonsedated
lamb underwent polysomnographic recordings on 3 consecutive days.
States of alertness, NNS and respiratory movements were recorded. Results
demonstrate that a CPAP of 6 cm H2O inhibited NNS during QS while administered
directly on the lower airways. This NNS inhibition was prevented by eliminating the
vagal afferent messages originating from the bronchopulmonary receptors. However,
application of CPAP on the upper airways only also inhibited NNS during QS. Finally,
the application of a CPAP 6 cm H2O had no systematic effect on NNS-breathing
coordination. In conclusion, our results suggest that the inhibiting effect of nasal
CPAP 6 cm H2O on NNS is mainly mediated by bronchopulmonary receptors with
some participation however of upper airway receptors. Our demonstration that
spontaneous, non-nutritive swallowing can be modulated by bronchopulmonary
receptor activity further illustrates the physiological interactions between upper and
lower airways