Origins of the inhibiting effects of nasal CPAP on nonnutritive swallowing in newborn lambs

Abstract

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...

Effects of nasal continuous positive-airway pressure on nutritive swallowing in lambs

“…Similarly, the present study indicates that nCPAP has no effect on NS-breathing coordination in full-term lambs. Overall, the coordination of breathing and NNS as well as NS appears to be largely unaltered by various conditions such as preterm birth (28), hypoxia (8), nCPAP, and nasal intermittent positive-pressure ventilation (33,34). Furthermore, the present results suggest that stimulation of positive pressure receptors in the upper airways by nCPAP, in likelihood with upper airway dilation, do not significantly alter NS in the neonatal period, including NS-breathing coordination.…”

“…Our previous studies (33,34) revealed that nCPAP had no systematic effect on NNS-breathing coordination in full-term lambs. Similarly, the present study indicates that nCPAP has no effect on NS-breathing coordination in full-term lambs.…”

“…Previous studies from our group showed an inhibiting effect of nCPAP on nonnutritive swallowing (NNS) in newborn lambs during quiet sleep, mediated by stimulation of both bronchopulmonary and upper airway receptors (33,34). In addition, continuous lung inflation prompted by application of negative extrathoracic pressure in awake adult humans was also shown to inhibit water-triggered swallows (14).…”

Radio telemetry devices to monitor breathing in non-sedated animals

“…Some progress has been made in the last years to decrease this stress, e.g. by using thoracic videosurgery instead of conventional thoracotomy Samson et al, 2008). However, we are continually committed to finding new ways to replace surgery by non-invasive instrumentation as often as possible, without decreasing the quality of recorded physiological signals.…”

“…Our group has been actively studying the perinatal control of breathing in lambs since the late 80's, in an attempt to better understand the pathophysiology of apneas of prematurity, apparent-life threatening events and sudden infant death syndrome, with a special focus on laryngeal physiology (Praud et al, 2006;Samson et al, 2007Samson et al, , 2008St-Hilaire et al, 2007).…”