Origins of the inhibiting effects of nasal CPAP on non-nutritive swallowing in newborn lambs

Abstract

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.