DEVELOPMENT OF HEART-RATE DYNAMICS DURING SLEEP-WALKING STATES IN NORMAL INFANTS

Previous studies show alterations in the dynamic patterns of cardiac r ate in several ''at-risk'' populations, including apparently healthy i nfants who subsequently die of the sudden infant death syndrome. In th e present study, we examined the maturation of cardiac rate dynamics i n normal infants during sleep-waking states over the first 6 mo of lif e. Instantaneous changes in cardiac RR intervals were examined in 12-h recordings of 24 normal full-term infants; each infant was recorded a t 1 wk and at 1, 2, 3, 4, and 6 mo of age. Scatter plots, consisting o f each cardiac R-R interval plotted as a function of the previous inte rval (Poincare plots), were constructed for each sleep-waking state in each recording. Analyses of variance were performed on the dispersion of intervals after long and short R-R intervals. In neonates, Poincar e plots showed significantly more next-interval dispersion after a lon g RR interval than after a short interval, a pattern similar to those observed in older infants and in healthy adults. However, between 1 wk and 1 mo of age, this pattern disappeared and returned gradually begi nning at 2 mo of age. The scatter of points in Poincare plots of infan ts 1 mo of age approached the patterns of at-risk populations, includi ng infants who subsequently died of the sudden infant death syndrome. These patterns at 1 mo may be indicative of increased vulnerability in normal infants after the neonatal period.