Postnatal maturation of laryngeal chemoreflexes in the preterm lamb

Abstract

Laryngeal chemoreflexes (LCR) are triggered by the contact of liquids with the laryngeal mucosa. In the mature organism, LCR trigger lower airway protective responses (coughing, effective swallowing, and arousal) to prevent aspiration. General belief holds that LCR are responsible for apnea and bradycardia in the newborn mammal, including humans. Our laboratory has recently shown that LCR in full-term lambs are consistently analogous to the mature LCR reported in adult mammals, without significant apneas and bradycardias (St-Hilaire M, Nsegbe E, Gagnon-Gervais K, Samson N, Moreau-Bussiere F, Fortier PH, and Praud J-P. J Appl Physiol 98: 2197–2203, 2005). The aim of the present study was to assess LCR in nonsedated, newborn preterm lambs born at 132 days of gestation (term = 147 days). The preterm lambs were instrumented for recording glottal adductor electromyogram, electroencephalogram, eye movements, heart rate, respiration, and oximetry. A chronic supraglottal catheter was used for injecting 0.5 ml of saline, distilled water, and HCl (pH 2) during quiet sleep, active sleep, and wakefulness on postnatal days 7 (D7) and 14 (D14). Laryngeal stimulation by water or HCl on D7 induced significant apneas, bradycardia, and desaturation, which, at times, appeared potentially life-threatening. No significant apneas, bradycardias, or desaturation were observed on D14. No consistent effects of sleep state could be shown in the present study. In conclusion, laryngeal stimulation by liquids triggers potentially dangerous LCR in preterm lambs on D7, but not on D14. It is proposed that maturation of the LCR between D7 and D14 is partly involved in the disappearance of apneas/bradycardias of prematurity with postnatal age.

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

“…On this basis, several neonatology teams are reluctant to initiate oral feeding in infants receiving nCPAP (23), probably fearing the cardiorespiratory consequences of triggering laryngeal chemoreflexes due to increased laryngeal penetration of milk. On one hand, previous results from our laboratory showing severe cardiorespiratory events in preterm lambs during laryngeal chemoreflexes triggered by milk during spontaneous room air breathing may be seen as giving support to these fears (37). On the other hand however, very recent unpublished observations by our group in preterm lambs that nCPAP (6 cmH 2 O) efficiently prevents these severe events justify further studies aiming at delineating the conditions where feeding can be attempted in newborns with nCPAP.…”

“…A number of neonatology teams refuse to initiate oral feeding in infants while on nCPAP (23), fearing laryngotracheal penetrations and pulmonary aspirations of milk with the consequent potentially deleterious cardiorespiratory events (27,37,38). On the other hand, some neonatologists defend the introduction of oral feeding in preterm infants while on nCPAP, as soon as cardiorespiratory stability is present (4,6).…”

Radio telemetry devices to monitor breathing in non-sedated animals

“…These unique models include apneas in premature lambs (Renolleau et al, 1999;St-Hilaire et al, 2007), application of nasal CPAP (Samson et al, 2005 or intermittent positive pressure ventilation , postnatal exposure to cigarette smoke (St-Hilaire et al, 2010), reflux laryngitis (Carreau et al, 2011), respiratory syncytial virus infection (unpublished results), all of which are relevant to neonatal respiratory problems. Overall, review of the scientific literature suggests that our team has the most extensive and consistent publication track record on respiration recording via radio telemetry.…”

“…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).…”

Presence of task-1 channel in the laryngeal mucosa in the newborn lamb

“…Furthermore, all of the above modulating factors of Task-1 channel activity appear especially relevant to the larynx. Indeed, extracellular acidification of the laryngeal mucosa is frequent during laryngo-pharyngeal reflux of acid gastric liquid and triggers the laryngeal chemoreflexes, which include swallowing, expiratory reflex and cough in the mature mammal in contrast to apnea, bradycardia and laryngospasm in the premature newborn mammal (16,17). Overall, the available literature suggests that laryngeal chemoreflexes are involved in apneas of prematurity, apparent life-threatening events of infancy and sudden infant death syndrome.…”