No abstract

Cardiorespiratory behavior during sleep has been investigated by comparing visually analyzed minutes of EEG sleep with the digitized values of these two physiologic variables for each corresponding minute. Continuous 3-h nighttime sleep studies on 37 full-term and preterm neonates at comparable postconceptional term ages were acquired under controlled conditions, using a 24-channel computerized monitoring system and an automated eventmarker program. Five thousand, two hundred ninety-four minutes were assigned an EEG state by traditional criteria. Eighteen preterm infants were compared with 19 full-term infants with respect to six cardiac and six respiratory measures: two nonspectral calculations (i.e. average per minute and variance of the means) and four spectral calculations of the cardiorespiratory signal (i.e. bandwidth, spectral edge, mean frequency, and ratio of harmonics). The relative capabilities of these measures to predict a sleep state change were investigated using discriminant analysis. A stepwise selection algorithm in discriminant analysis was used to identify the order of significance for the remaining variables. Eight cardiorespiratory measures were then submitted to multivariate analysis of variance to assess sleep state or preterm-full-term differences: mean frequency, bandwidth, average per minute, and ratio of harmonics for cardiac signals; and spectral edge, mean frequency, logarithm of variance, and ratio of harmonics for respiratory signals. Differences among the sleep states and between neonatal groups were highly significant ( p < 0.0001). Interaction between sleep state and neonatal group was also significant ( p < 0.034). Two variables differentiated preterm from full-term respiratory behavior: ratio ( p I 0.001) and mean frequency ( p 5 0.02). Three variables demonstrated differences between preterm and full-term cardiac behavior: average heart rate per minute ( p I 0.001), ratio ( p I 0.05), and bandwidth ( p I 0.08). Notably, the lowest values for most spectral measures were noted during tract5 alternant quiet sleep compared with the three other segments of the ultradian sleep cycle. Our findings demonstrate sleep state-specific differences in cardiorespiratory behavior in neonates regardless of prematurity. Differences between preterm and full-term infants reflect altered functional development of the brain because of adaptation to prematurity, an extrauterine experience, or both and may contribute to a model of physiologic vulnerability of certain infants for sudden infant death syndrome. (Pediatr Res 36: 738-744, 1994) Abbreviations SIDS, sudden infant death syndrome EEG sleep organization, in general, is comparable for have been described between full-term and preterm inall newborns at postconceptional term ages regardless of fants in cardiorespiratory behavior, rapid eye moveprematurity at birth (1, 2). However, differences also ments, spectral content, and state organization (3-11).W e have reported differences between full-term and Received April 16, 1993; accepted May 18, ...

Different physiologic measures during EEG sleep peri-discontinuous periods of EEG activity (i.e. quiet sleep). ods in preterm neonates are postulated to change with Sleep efficiency (p < 0.001), maintenance ( p < 0.001), and maturation and reflect functional brain development. For-latency (p = 0.01) also decreased with increasing postconty-three healthy preterm neonates received 3-h EEG sleep ceptional age. Cycle length between two segments of constudies in an environmentally controlled setting. Postcon-tinuous EEG with an intervening period of EEG disconticeptional ages of neonates at each recording session ranged nuity also lengthened with maturation ( p < 0.001). These from 28 to 35 wk. Minute-by-minute analyses of EEG findings are discussed in the context of previously reported discontinuity, motility, arousals, and REM were per-differences in phasic and continuity measures noted beformed. Eight phasic events and continuity measures of tween preterm and full-term infants at matched full-term sleep were tabulated. Data were analyzed using Spearman postco~ceptional ages. Changes in phasic and continuity rank order correlation coefficients. Increases in arousal measures with increasing postconceptional ages reflect numbers ( p < 0.001) and durations ( p < 0.001) were noted maturation of specific neuronal processes of the CNS with age only during continuous periods of EEG activity within a rudimentary sleep cycle of the preterm neonate. The concept of state during early brain ontogenesis of the preterm infant is controversial. It is generally accepted that patterns representing sleep in preterm infants are highly variable (1) and less organized than patterns described for full-term infants (24). Conventional wisdom dictates that organized sleep states do not appear before 31 w k (1, 2) and are not well established until 36 w k postconceptional age (1-6). Several researchers, however, have questioned this assumption based on studies of sleep in preterm infants. Rudimentary state differentiation in terms of motor, EEG discontinuity, and autonomic function have recently been described in early preterm infants (4,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Although four well-developed Received February 8, 1993; accepted May 18, 1994. Correspondence and reprint requests: Mark S. Scher, M.D., Developmental Neurophysiology Laboratory, Magee-Womens Hospital, 300 Halket St., Pittsburgh, PA 15213-3180. Supported in part by Grants NSO1110, NS26793, and MOlRR00084, the Twenty-Five Club of Magee-Womens Hospital, and the Scaife Family Fund.'Presented in part at the 7th International Child Neurology Meeting, Buenos Aires, Argentina, November 1992. sleep state segments of the full-term infant are not observed on the EEG recordings of preterm infants, specific physiologic measures may already have an established association during specific segments of the rudimentary EEG sleep cycle.Studies of the maturational trends of polysomnographic measures in asymptomatic, presumably healthy neonates will assist in the documenta...