Reflex Apnea from Laryngeal Chemo-Stimulation in the Sleeping Premature Newborn Lamb

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Abstract
Summary: The laryngeal chemoreflex was studied during quiet and REM sleep and wakefulness in premature newborn lambs. The response to reflex stimulation with a 5 sec-water infusion was evaluated during 30 sec, as % change in ventilation, heart rate and blood pressure. Apnea, hypertension and bradoardia were more pronounced during sleep than during walleffilhess, when arousal was not associated with the stimulation. The response was similar during quiet and REM sleep. Arousal, which occurred in 24 and 31% of the tests respectively, resulted in a response comparable to that seen during wakefulness. The respiratory drive was evaluated by measurement of the mean inspiratory flow and was found to be decreased during both sleep states when compared to wakefulness. We propose that during sleep in the newborn period there is a decreased ability to respond to asphyxia possibly due to a functional immaturity of the arterial chemoreceptors. This results in a low incidence of arousal and a delayed termination of the pronounced poststimulus apnea resulting from laryngeal chemoreflex stimulation. Speculation: In the newborn lamb, quiet and REM sleep have been shown to be more vulnerable states than wakefulness to reflex apnea elicited by laryngeal chemoreflex stimulation with water, probably as a reflection of decreased respiratory drive and a failure to arouse. It is possible that reflex apnea during sleep triggered by a variety of mechanisms may play a role in the pathogenesis of Sudden Infant Death Syndrome (SIDS).