Heart Rate Variability during Sleep and Wakefulness in Low-Birthweight Infants

Abstract

The effects of various stages of sleep and wakefulness on heart rate were studied, with R-R interval histograms computed by a ATAC computer, in serial polygraphic EEG recordings made on 22 low-birthweight infants. The heart rate depended on postnatal age rather than on conceptional age, decreasing progressively after birth to each a minimum at various days between 7 and 30 days old, followed by a gradual increase. The heart rate was higher during stage 3 than during stage REM. The heart rate variability was greatest during stage REM and stage 1; it was smallest during stage 3. During crying and bottle feeding, the variability was as small as during stage 3. The variability during wakefulness was larger than during stage 3, but far smaller than during stage REM. The heart rate was very regular, and without the changes associated with sleep stages in infants of 25 to 30 weeks’ conceptional age.