Quantitative sleep stage analyses as a window to neonatal neurologic function

Abstract

Objective: To test the hypothesis that neonatal sleep physiology reflects cerebral dysfunction, we compared neurologic examination scores to the proportions of recorded sleep/wake states, sleep depth, and sleep fragmentation in critically ill neonates.

Methods: Newborn infants (≥35 weeks gestation) who required intensive care and were at risk for seizures were monitored with 8- to 12-hour polysomnograms (PSGs). For each infant, the distribution of sleep-wake states, entropy of the sequence of state transitions, and delta power from the EEG portion of the PSG were quantified. Standardized neurologic examination (Thompson) scores were calculated.

Results: Twenty-eight infants participated (mean gestational age 39.0 ± 1.6 weeks). An increased fraction of quiet sleep correlated with worse neurologic examination scores (Spearman rho = 0.54, p = 0.003), but the proportion of active sleep did not (p > 0.1). Higher state entropy corresponded to better examination scores (rho = -0.43, p = 0.023). Decreased delta power during quiet sleep, but not the power at other frequencies, was also associated with worse examination scores (rho = -0.48, p = 0.009). These findings retained significance after adjustment for gestational age or postmenstrual age at the time of the PSG. Sleep stage transition probabilities were also related to examination scores.

Conclusions: Among critically ill neonates at risk for CNS dysfunction, several features of recorded sleep-including analyses of sleep stages, depth, and fragmentation-showed associations with neurologic examination scores. Quantitative PSG analyses may add useful objective information to the traditional neurologic assessment of critically ill neonates.

Figures

Figure 1. Lower delta power during quiet sleep is associated with worse neurologic examination scores

On the EEG, lower delta frequency power (0.5–4 Hz) during quiet sleep was associated with worse neurologic examination (Thompson) scores (Spearman correlation p < 0.05, open circles). The EEG power at higher frequencies did not correlate with examination scores (p > 0.05, crosses).

Figure 2. Sleep-wake stage transition probabilities for 28 critically ill neonates

Sleep-wake stage transition probabilities for 28 critically ill neonates monitored with polysomnography. Those with Thompson scores at or below the group median (i.e., t test p = 0.02 for difference in mean transition probabilities). The Spearman correlation of active to quiet sleep transition probability with Thompson score was rho = 0.5, p = 0.006.