SummaryThe time spent in REM, quiet, and indeterminate sleep was computed in 13 aborted SIDS infants and compared to that spent in the same sleep states .in 19 normal infants. Aborted sudden infant death syndrome (SIDS) infants were studied within a week of their aborted SIDS episode and subsequently at monthly intervals through the age of 4 months. Normal infants were studied at 1,2,3, and 4 months of age. Sleep staging was performed by two independent observers using electroencephalogram, electrooculogram, electromyogram and behavioral criteria. Although there was an increase in the percentage of time spent in quiet sleep with age in both normal and aborted SIDS infants, the significantly greater regression coefficients in normal infants (6.3 versus 2.9; P < 0.01) indicate that there are differences in the two groups and suggest a maturational abnormality or delay in sleep state distribution in aborted SIDS infants.
SpeculationThe results of this study suggest that the differences in sleep state distribution between aborted sudden infant death syndrome and normal infants share a common pathophysiologic alteration with the ventilatory and cardiac abnormalities reported by us elsewhere, perhaps involving the catecholaminergic system. Previous studies from this laboratory have demonstrated that infants with aborted sudden infant death syndrome (SIDS) have increased heart rate and decreased heart rate variability (7), smaller QT index (3), and a greater COz-induced increase in minute ventilation (4) than do normal infants during both REM and quiet sleep. We have hypothesized that these findings are most consistent with an increase in the level of sympathoadrenal activity. Because the activity of the autonomic nervous system fluctuates during each sleep state, especially during REM sleep (2), we asked whether these ventilatory and cardiac differences depend on differences in the time spent in each sleep state. We, therefore, compared the time spent in REM, quiet, and indeterminate sleep in 13 aborted SIDS infants and in 19 age-matched normal infants during serial observations at monthly intervals in the first 4 months of life.
MATERIALS AND METHODS
STUDY POPULATIONWe defined an aborted SIDS infant as one who has experienced at least one episode of unexplained apnea and unresponsiveness with cyanosis or pallor requiring mouth to mouth resuscitation or vigorous physical stimulation for revival. The mean age of the infants at the time of the first aborted SIDS episode was 2 months, with a range of 1 to 4 months. Nine of the 13 infants were observed to be asleep shortly before their apneic episode; the level of 1 Of consciousness was unknown in the remaining four. Detailed clinical and laboratory assessment failed to reveal an explanation for the aborted SIDS episode. The laboratory evaluation included blood counts, serum glucose, calcium, magnesium, sodium, potassium and chloride, acid-base and blood gas analysis, chest x-ray, conventional 12-lead electrocardiogram, an electroencephalogram (EEG), and a roentgenographi...