SLEEP STATE ORGANIZATION IN PREMATURE-INFANTS OF LESS-THAN-35-WEEKS GESTATIONAL-AGE

To assess sleep organization in premature infants of <35 wk gestationa l age (w GA), we performed polygraphic recordings in 24 neurologically normal neonates (eight per group): artificially ventilated 27-30 and 31-34 w GA infants and nonventilated 31-34 w GA infants. Sleep states were defined by concordance of EEG and rapid eye movement criteria. Un interrupted active sleep periods of >13 min and quiet sleep periods of >5 min were observed in all babies, except in one 33 w GA ventilated infant. Intervals from the beginning of recording to the 1st quiet sle ep period varied from 0 to 63 min and intervals to the beginning of th e longest sleep cycle varied from 5 to 84 min. Nonventilated 31-34 w G A infants had longer sleep cycles (p < 0.02), principally because of l onger active sleep periods. However, percentages of different states i n the cycles were similar in all groups. When body movements were requ ired for state definition, amounts of active and quiet sleep diminishe d and the percentage of indeterminate sleep was augmented significantl y. In conclusion, our study demonstrated that I) sleep state different iation is present as soon as 27 w GA; and 2)artificial ventilation, pe rformed in a highly specialized neonatal intensive care unit, does not modify sleep organization of neurologically normal premature infants. We hypothesize that this ''earlier'' sleep state differentiation, com pared with previous data, may be related to improvements in neonatal i ntensive care over recent years.