The present study stems from our recent demonstration (Moreau-Bussiere F, Samson N, St-Hilaire M, Reix P, Lafond JR, Nsegbe E, Praud JP. J Appl Physiol 102: 2149-2157, 2007) that a progressive increase in nasal intermittent positive pressure ventilation (nIPPV) leads to active glottal closure in nonsedated, newborn lambs. The aim of the study was to determine whether the mechanisms involved in this glottal narrowing during nIPPV originate from upper airway receptors and/or from bronchopulmonary receptors. Two groups of newborn lambs were chronically instrumented for polysomnographic recording: the first group of five lambs underwent a two-step bilateral thoracic vagotomy using video-assisted thoracoscopic surgery (bilateral vagotomy group), while the second group, composed of six lambs, underwent chronic laryngotracheal separation (isolated upper airway group). A few days later, polysomnographic recordings were performed to assess glottal muscle electromyography during step increases in nIPPV (volume control mode). Results show that active glottal narrowing does not develop when nIPPV is applied on the upper airways only, and that this narrowing is prevented by bilateral vagotomy when nIPPV is applied on intact airways. In conclusion, active glottal narrowing in response to increasing nIPPV originates from bronchopulmonary receptors.

The present study investigated the mechanism by which continuous positive airway pressure (CPAP) suppresses nonnutritive swallowing (NNS) during quiet sleep (QS) in newborn lambs. Eighteen full-term lambs were chronically instrumented and evenly distributed into three separate groups to determine the extent to which modulation of NNS may be attributed to stimulation of upper airway and/or bronchopulmonary mechanoreceptors. Six lambs were tracheotomized, six other lambs underwent a two-step bilateral intrathoracic vagotomy, and the remaining six lambs underwent chronic laryngotracheal separation (isolated upper airway group). Forty-eight hours after surgery, each nonsedated lamb underwent polysomnographic recordings on three consecutive days. States of alertness, NNS and respiratory movements were recorded. Results demonstrate that a CPAP of 6 cmH2O inhibited NNS during QS while administered directly on the lower airways and that bivagotomy prevented this inhibition. However, application of CPAP on the upper airways only also inhibited NNS during QS. Finally, the application of a CPAP of 6 cmH2O had no systematic effect on NNS-breathing coordination (assessed by the respiratory phase preceding and following NNS). In conclusion, our results suggest that bronchopulmonary receptors are implicated in the inhibiting effects of nasal CPAP of 6 cmH2O on NNS in all our experimental conditions, whereas upper airway receptors are only implicated in certain conditions.nasal and tracheal continuous positive airway pressure; vagotomy; laryngotracheal separation; bronchopulmonary receptors NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP) has been used in newborns for a number of years for treating respiratory distress syndrome and apneas of prematurity and as a bridge between endotracheal tube ventilation and spontaneous ventilation (4, 6, 10). However, laryngeal functions, such as nonnutritive swallowing (NNS), which fulfils the important task of clearing upper airways from secretions and liquids refluxed from the stomach, have not been specifically assessed in newborns during nasal CPAP, aside from one study wherein nasal CPAP was shown to increase laryngeal opening (5). We recently reported that a nasal CPAP of 6 cmH 2 O inhibits spontaneous NNS in newborn lambs during quiet sleep (QS) (19). Although such effects were previously reported for waterinduced swallowing in conscious adult humans (12), the precise mechanism by which swallowing is inhibited by nasal CPAP remains unclear. Recent findings suggest it may be mediated by mechanoreceptors in the upper airways or by bronchopulmonary slowly adapting stretch receptors (SARs). Indeed, a recent study showed that application of CPAP on isolated larynx enhances laryngeal constrictor muscle (thyroarytenoid) activity in piglets (22). Alternatively, continuous lung inflation induced by negative extrathoracic pressure in awake adult humans also inhibits water-triggered swallows (7), suggesting that SARs can modulate swallowing. According to the authors, the latter hypothesis was f...