Maturation of phasic and continuity measures during sleep in preterm neonates

Different physiologic measures during EEG sleep periods in preterm neonates are postulated to change with maturation and reflect functional brain development. Forty-three healthy preterm neonates received 3-h EEG sleep studies in an environmentally controlled setting. Postconceptional ages of neonates at each recording session ranged from 28 to 35 wk. Minute-by-minute analyses of EEG discontinuity, motility, arousals, and REM were performed. Eight phasic events and continuity measures of sleep were tabulated. Data were analyzed using Spearman rank order correlation coefficients. Increases in arousal numbers (p < 0.001) and durations (p < 0.001) were noted with age only during continuous periods of EEG activity (i.e. active sleep). REM also increased with corrected age during indeterminate or transitional sleep (p < 0.002) and decreased during quiet sleep (p < 0.01). Decreases in small body movements per minute (p = 0.02) and large body movements per minute (p < 0.001) occurred only during discontinuous periods of EEG activity (i.e. quiet sleep). Sleep efficiency (p < 0.001), maintenance (p < 0.001), and latency (p = 0.01) also decreased with increasing postconceptional age. Cycle length between two segments of continuous EEG with an intervening period of EEG discontinuity also lengthened with maturation (p < 0.001). These findings are discussed in the context of previously reported differences in phasic and continuity measures noted between preterm and full-term infants at matched full-term postconceptional ages. Changes in phasic and continuity measures with increasing postconceptional ages reflect maturation of specific neuronal processes of the CNS within a rudimentary sleep cycle of the preterm neonate.