Philippe Reix

Non-nutritive swallowing and respiration coordination in full-term newborn lambs.

Swallowing is a powerful inhibitor of respiratory rhythm in infants. The present study was aimed at investigating the influence of states of alertness on non-nutritive swallowing (NNS) frequency, on NNS and respiration coordination, and on bursts of NNS frequency in newborn lambs. Six full term newborn lambs were instrumented for electroencephalogram, eye movement, diaphragm and thyroarytenoid muscle electromyogram, nasal flow and electrocardiogram. Polysomnographic recordings were performed in non-sedated lambs, using radiotelemetry. NNS frequency was significantly higher during quiet wakefulness (W) and active sleep (AS) than during quiet sleep (QS). NNS mainly interrupted inspiration and the transition phases between expiration and inspiration, especially in W and AS. Bursts of NNS occurred significantly more often during AS. This study highlights the relevance of the ovine model to study ontogeny of NNS during sleep, and documents the influence of sleep on NNS and respiration coordination.

Effects of C fiber blockade on cardiorespiratory responses to laryngeal stimulation in concious lambs

The primary aim of the study was to explore cardiorespiratory reflexes originating from laryngeal C fiber endings in the neonatal period. Seventeen lambs were instrumented for recording glottal adductor and diaphragm EMG, heart rate, systemic arterial pressure and respiratory movements. C fiber blockade was induced in eight lambs by 30 mg/kg capsaicin, the remaining nine lambs serving as controls. Cardiorespiratory reflexes were induced in non-sedated lambs by flowing air, menthol or 13% CO2, or by injecting water or 50 microg capsaicin in the laryngeal inlet through an endoscope. Responses to all stimuli but capsaicin were similar between the two groups. While cardiorespiratory responses were induced by capsaicin in control lambs, the responses were significantly inhibited in lambs with C fiber blockade. We conclude that laryngeal C fiber endings are functional and responsible for laryngeal chemoreflexes in newborn lambs.

Cricothyroid muscle electrical activity during respiration and apneas in lambs

Respiratory function of the cricothyroid muscle (CT) is virtually unknown in the neonatal period. This study was aimed at assessing CT electrical activity (EMG) during respiration and central apneas in non-sedated lambs. Seven full-term and four preterm lambs were instrumented for polysomnographic recording, including EMG of the diaphragm, thyroarytenoid (TA, a glottal constrictor), posterior cricoarytenoid (PCA, the primary glottal dilator) and CT. Phasic CT EMG was usually observed during inspiration and late expiration, whereas phasic TA EMG was observed during early expiration. While TA EMG virtually disappeared in REM sleep, both inspiratory and expiratory CT EMG increased. Overall, while CT EMG was not frequently observed during central apneas in either full-term (10% of apneas, but never simultaneously with TA EMG) or preterm lambs (30% of apneas), it was associated with decreased lung volume and subglottal pressure when present alone or with PCA EMG. Our results concur with the assumption that CT behaves as a laryngeal dilator in the neonatal period.

Influence of Prematurity on Postnatal Maturation of Heart Rate and Arterial Pressure Responses to Hypoxia in Lambs

Background: While hypoxic events with bradycardias are a frequent occurrence during the first weeks of life in preterm infants, the impact of preterm birth on maturation of the cardiovascular response to hypoxia in early postnatal life is unknown. Objectives: In the present study, we tested the hypothesis that preterm birth influences postnatal maturation of cardiovascular responses to hypoxia. Methods: 6 preterm lambs (term 132 days, birth weight 2.9 kg) and 6 full-term lambs (term 147 days, birth weight 4.3 kg) were studied without sedation on days 3, 7, 14, 21 and 28 during acute, steady-state hypoxia (FIO2 = 0.08, 15 min). Results: Results show that full-term lambs increased their heart rate (HR) in response to hypoxia from the first day of life, with no postnatal maturation thereafter. In preterm lambs, HR did not change before day 14 and the full-term-like response was not acquired before 2 weeks after theoretical term. In both groups, mean arterial pressure tended to decrease below baseline, but the amplitude of variations remained of small magnitude. Conclusion: The present results bring unique evidence that preterm birth is associated with a blunted heart response to steady-state hypoxia during the first postnatal week and a delay in the maturation of HR response.

Monitoring pulse oximetry via radiotelemetry in freely-moving lambs

This study was aimed at validating the use of a custom-made wireless pulse oximeter in freely moving lambs, using radiotelemetry transmission. First, measurements obtained simultaneously using the new, wireless oximeter and a standard commercially-available pulse oximeter (Nonin 8500) were compared in five lambs during 5min episodes of normoxia, hypoxia and hyperoxia. Correlation between the two oximeters for both SpO(2) and heart rate was very good, regardless of oxygenation conditions. Secondly, the capabilities of our device were assessed during more than 45h of polysomnographic recordings in seven lambs. According to the plethysmographic pulse waveform, reliable SpO(2) values were obtained in more than 85% of recording time. Multiple decreases in SpO(2) were readily observed after spontaneous apneas in preterm lambs. It is concluded that our wireless pulse oximeter performs as reliably as a standard pulse oximeter for monitoring SpO(2) variations in lambs, and offers new perspectives for researchers interested in continuous monitoring of oxygenation throughout sleep stages and wakefulness.