Airway closure during mixed apneas in preterm infants: Is respiratory effort necessary?

Airway closure during mixed apneas in preterm infants may be due to lack of tone in the upper airway followed by collapse and obstruction or diaphragmatic action inducing obstruction. We examine whether respiratory efforts are necessary for airway closure using a new method of detecting airway obstruction, based on the disappearance of an amplified cardiac pulse observed on the respiratory flow tracing. We analyzed 198 episodes of mixed apnea of various lengths (≥3 seconds) observed in 33 preterm infants (birth weight, 1.4 ± 0.1 kg [mean ± SEM]; study weight, 1.7 ± 0.1 kg; gestational age, 29 ± 1 weeks; postnatal age, 33 ± 4 days). The great majority of these episodes (88%) had a central, followed by an obstructive, component. Infants were studied by using a nosepiece and a flow-through system. Respiratory efforts (abdominal and chest movements) were recorded. Of the apneas, 20 were