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UPPER AIRWAY OBSTRUCTION DURING APNEIC SPELLS IN PRETERM INFANTS

Apneic spells can result from respiratory muscle inactivity (central apnea) and also from obstruction to air flow (obstructive apnea). Manually flexing the neck of infants can result in a mixture of obstructive and central apnea (J. Pediat. 89:982). To study the effect of spontaneous neck flexion on apnea frequency and mechanism we recorded expiratory flow (nasal CO2 probe, mouth closed) respiratory muscle activity (swings in esophageal pressure) and EKG in 8 preterm infants (4 with apnea of prematurity and 4 controls). Infants were observed for 1 hr. in a supine posture alternating with a posture predisposing to spontaneous neck flexion (infant seat elevated to 45°-75°). 42 spells defined as absent air flow ≥120 sec. or absent flow < 20 sec. followed by heart rate ≤ 100/min, occurred in 6 infants including 10 spells in 2 controls. Spells were 2X as frequent sitting than supine and while sitting, 4X as frequent with the neck flexed than not. The mechanism of most spells was mixed regardless of posture. Thus, 35 of 42 spells consisted of obstructed breaths (respiratory muscle activity without flow) alternating with central apnea; in 14 of 35 obstruction preceded central apnea. Only 3 spells were central. Conclusion: airway patency is potentially a significant factor in the pathogenesis of apnea of prematurity. Spontaneous neck flexion predisposes to apneic spells possibly by increasing an inherent vulnerability to upper airway obstruction.