Postnatal autonomic activity in the preterm lamb

BackgroundEarly postnatal abnormalities of autonomic nervous system (ANS) activity, including at baseline and following cardiorespiratory challenge, are involved in apneas–bradycardias of prematurity, apparent life-threatening events of infancy and sudden infant death syndrome. Literature data suggest that baseline ANS activity does not mature normally after premature birth.ObjectivesThis study performed in preterm lambs was aimed at assessing ANS maturation at baseline and following laryngeal chemoreflexes (LCR), a group of reflexes triggered by the contact of liquids with the laryngeal mucosa.MethodsHeart rate variability (HRV) and baroreflex sensitivity (BRs) were measured at baseline and after LCR during polysomnographic recordings performed in five non-sedated lambs born 15 days prematurely. Laryngeal chemoreflexes were induced by distilled water or acid (pH 2) during sleep and wakefulness on postnatal days 7 (D7) and 14 (D14, full-term equivalence).ResultsWhile the life-threatening cardiorespiratory events of the LCR observed at D7 were no longer present at D14, baseline and post-LCR HRV and BRs indices were significantly lower at D14 compared to D7 (up to p < 0.001). These results suggest that an initial autonomic overactivity was present at D7 and normalized at D14.ConclusionThe autonomic cardiac and baroreflex control appears to follow a specific evolution in the preterm compared to the full-term newborn lamb, with an important initial autonomic stress, which normalizes at an age equivalent to full-term. Potential relevance of these findings in relation to anomalies of cardiac control in the early postnatal period, such as apneas–bradycardias of prematurity, apparent life-threatening events of infancy and sudden infant death syndrome, awaits further studies.