Respiratory frequency according to sleep states and age in normal premature infants: A comparison with full term infants

Abstract

To assess the influence of sleep states, gestational age, and postnatal age on respiratory frequencies, we made polygraphic recordings on forty-eight 31-41 wk gestational age newborns (≤ 10 days of legal age) and on 16 prematurely born (≤ 36 wk of gestation) infants, after they reached the term of 37-40 wk conceptional age. Periods with and without ≥3-sec respiratory pauses were independently analyzed by 20-sec periods. States of sleep were defined according to REMs and EEC criteria. At all ages and in all sleep states, respiratory frequencies were slightly, but not significantly, lower in total tracing compared to no-pause tracing. Results of statistical comparison were identical when they were performed on both total and no-pause tracings. From 35 wk gestational age onward, respiratory frequency was higher in active (AS) REM sleep, compared to quiet (QS) NREM sleep (P < 0.01). In undefined sleep (IS), respiratory frequency was at an intermediate level (AS > IS > QS), significantly different from that of AS and QS. Respiratory frequency was similar in all 31-38 wk gestational age newborns. It became significantly higher in 39-41 wk gestational age newborns (P < 0.01). The frequency of the respiration was higher in prematurely born infants reaching 37-48 or 39-40 wk conceptional age, compared to that of newborns of the same gestational age. We did not find significant differences between genders in any age group studied. At all ages there was a high correlation among respiratory frequencies found in AS, QS, and IS and also among those frequencies found in successive sleep cycles for given individuals: Some normal infants breathed more rapidly and the others more slowly in all states studied. It appears that respiratory frequency is an individual characteristic, modulated by the sleep state, gestational age and postnatal age factors. The review of the literature suggests, that divergences among authors can be due to some methodological differences and partic-ularly to differences in scoring of sleep states. © 1983 International Pediatric Research Foundation, Inc.