Airway Closure During Mixed Apneas in Preterm Infants: Is Respiratory Effort Necessary? • 1800

Abstract

The exact mechanism for airway closure during mixed apneas in preterm infants is unknown. One possibility is that lack of tone in the upper airway is followed by collapse and obstruction; another possibility is that the diaphragmatic action sucks the upper airway in and induces obstruction. We took advantage of our new method of detecting airway obstruction, based on the disappearance of a magnified cardiac pulse observed on the respiratory flow, to examine whether respiratory efforts are necessary for airway closure. We analyzed 198 mixed apneas of various lengths (≥3 s) observed in 33 preterm infants [birthweight 1400±100 g (mean±SE), study weight 1745±120 g; gestational age 29±1 wk, postnatal age 33±4 d]. The great majority of these apneas (88%) had a central followed by an obstructive component. The infants were studied using a nosepiece and a flow-through system. Respiratory efforts (abdominal and chest movements, diaphragmatic EMG) were recorded. Of the apneas, 20 were less than 5 second duration; 78, 5 to 10 seconds; 45, 10 to 15 seconds; 27, 15 to 20 seconds; and 28 greater than 20 seconds. Of the 198 mixed apneas, 151 occurred in the absence of any respiratory effort; 43 showed a simultaneous cessation of the cardiac oscillation and respiratory effort; and 4 showed diaphragmatic activity appearing after cessation of the cardiac oscillation. There was never any evidence of respiratory efforts preceding the cessation of the cardiac oscillation. The findings suggest 1) the diaphragmatic action is not needed to occlude the airway in mixed apneas, since most of them occlude without diaphragmatic activity, and in some such activity follows the closure of the airway; and 2) the simultaneous occlusion of the airway with the beginning of respiratory efforts in 43 apneas may indicate that such effort contributes to closure or is induced by the same stimulus that closes the airway. We speculate that the mechanism for airway closure in mixed apneas is most likely a lack of upper airway tone, which normally occurs simultaneously with the cessation of a central drive to breathe.Supported by the Children's Hospital of Winnipeg Research Foundation.