The effects of airway closure in central apneas and obstructed respiratory efforts in mixed apneas in preterm infants.

Background: Airway closure during central apnea could allow for better gas exchange. However, the return of inspiratory efforts against a closed airway may cause greater desaturation and prolongation of apnea.

Objective: To investigate the effect of patency of the airway and obstructed respiratory efforts on the length of apneas and the degree and slope of O(2) desaturation and bradycardia.

Methods: All mixed apneas observed in 15 preterms were matched 1:2 with the longest central apneas in each infant. Central apneas were further classified using the amplified cardiac airflow oscillation in those with airway open and in those with airway closed.

Results: No differences were found in the length of apnea, slope of O(2) desaturation, delay between the onset of apnea and onset of desaturation, lowest post-apneic SpO(2), and time of recovery of SpO(2) between central apneas with and without airway closure. Although mixed apneas were significantly longer than central apneas, their initial central component was significantly shorter than the length of central apneas. In mixed apneas, the onset of O(2) desaturation occurred faster, SpO(2) decreased lower, and recovered slower compared with central apneas. The slope of O(2) desaturation after the obstructed respiratory efforts was significantly greater than before the obstructed respiratory efforts.

Conclusions: In preterm infants: (1) airway closure during central apneas does not limit oxygen desaturation; (2) respiratory efforts against a closed airway prolong apnea and worsen the degree of desaturation and bradycardia. Although respiratory efforts are not necessary to induce airway closure, inspiratory efforts against a closed airway could trigger inhibitory cardio-respiratory responses causing significant desaturation, bradycardia, and prolongation of apnea.