1515 RESPIRATORY TIMING IN NEWBORNS WITH RESPIRATORY DISTRESS SYNDROME (RDS)

The Hering-Breur inspiratory inhibitory reflex decreases in activity with increasing gestational age (GA) (JAP 36:426). An intercostal-phrenic inhibitory reflex may be present in the premature with RDS who demonstrates paradoxical rib cage motion (JAP 40:352). Either reflex would decrease inspiratory time (Ti) in premature infants of younger (GA). We tested the hypothesis that Ti is directly proportional to GA in infants with RDS resulting in a greater respiratory rate (f) in the less mature newborn. Ti and f were calculated from nasal or oral flow signals in 6 spontaneously breathing infants with RDS at 6-14 hrs of age. Infants were studied supine during REM sleep using behavioral criteria. Mean Ti and f for a 5 minute period were determined from the flow tracings. Contrary to our hypothesis, Ti decreased with increasing GA (r=-0.889, p=0.018). If inspiratory inhibitory reflexes are more active in the premature newborn of younger gestation with RDS, their effect was not sufficient to produce a smaller Ti when compared to more mature infants. Either these reflexes are not present in infants with RDS or other factors may have a greater influence on respiratory timing.