1691 APNEA FROM LARYNGEAL CHEMOREFLEX (LCR) STIMULATION DURING SLEEP IN THE NEWBORN LAMB

Abstract

In order to evaluate the effects of different activity states (AS): wakefulness (W), Rapid Eye Movement (REM), and Quiet Sleep (QS), on the recovery from LCR induced apnea, we studied 4 premature newborn lambs chronically instrumented with tracheostomy, EEG and EOG leads for 1 to 5 weeks. During each AS, the LCR was stimulated with water for 5 s. The response was evaluated as the % decrease in ventilation from the baseline period for 30 s after the onset of stimulation (ΔV). ΔV was greater during REM (85.9±17.8)+and QS (82.4±17.3) than during W (55.9±21.5)*, but there was no difference between REM and QS. Following arousal, which occured in 1/4 of the tests during sleep, the response was markedly reduced (ΔV=53.7±28.6). However, one lamb needed frequent resuscitation after stimulation during either REM or QS. Respiratory drive for each AS was evaluated during the baseline period by measuring mean inspiratory flow (Tidal Volume/Inspiratory Time: Vt/Ti), assuming no variations in lung resistance among different AS. Vt/Ti was lower during either QS (55.7±19.7) or REM (50.4±14.5) as compared to W (70.5±33.5)*. During both REM and QS, if arousal does not occur, the newborn lamb is more vulnerable to LCR stimulation induced apnea which can be fatal. A more sustained apnea during sleep may be related to a decreased respiratory drive and/or a decreased sensitivity to hypoxemia. It is postulated that, although the importance of such reflex apnea in the human infant is unknown, the impaired recovery observed during sleep may reproduce the sequence of events occuring in SIDS.