SummaryThe 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 bra-rdia were more pronounced during sleep than during watieffilhess, 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.
SpeculationIn 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).The inhibitory effect on respiration of superior laryngeal nerve stimulation was first recognized by Rosenthal in 1862 (43). Several investigators have since studied extensively the reflex elicited by the stimulation of the laryngeal chemoreceptors (5,6,19,21,22,25,26,29,46). Stimulation of the laryngeal chemoreflex (LCR) in the unanesthetized animal elicits a multi-organ response: apnea, swallowing, bradycardia, increase in pulmonary and systemic vascular resistances and blood flow redistribution in the dive pattern with preservation of cerebral and myocardial perfusion. The afferent pathway of the reflex lies in the superior laryngeal nerve. Previous reports in anesthetized newborn animals have shown that this reflex apnea can be lethal (13,26,33,48).SIDS victims usually die during the night, presumably because of failure to recover from apnea during sleep. Both quiet (2,18,20,44) and REM sleep (12,17,18,23,28,48) have been implicated as being vulnerable activity states for apnea in the newborn period, especially in premature infants. A recent study in the unanesthetized adult dog has described the depressed arousal response from REM sleep occurring after LCR stimulation (47); however, little is known about the influence of different activity states on the LCR response in newborn animals.This study was performed in unanesthetized premature newborn lambs in order to evaluate the effects of different activity states on the respiratory and cardiovascular response to laryngeal chemoreflex stimulation. The study lambs wer...
