Heart rate variability in response to the sleep-related movements in infants with and without colic

The activity of the autonomic nervous system depends on sleep stage. The imbalance of the autonomic nervous system together with over-reactivity to stimuli has been suggested to be an etiologic factor for infantile colic. This study was designed to estimate the reactivity of the autonomic nervous system to a sleep-time stimulus in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep stages and in colic and control infants. Overnight sleep polygraphic recordings were performed for 12 colic and 14 control infants at the age of 8 weeks. Movements were detected by a static-charge-sensitive bed. Extent of heart rate variability (HRV) was measured in response to spontaneous sleep-related movements. HRV analysis was performed over 2-min segments during NREM and REM sleep before and after 5-36-s long movement periods. Total (0.04-1.0 Hz), low (0.04-0.15 Hz) and high frequency (0.15-1.0 Hz) HRV increased after the movement periods in light NREM sleep (p < 0.001). These changes were not observed in REM sleep. No differences were found between the colic and the control groups in HRV. The observed difference in the response of the HRV between sleep stages is likely to reflect the different characteristics of heart rate control in NREM and REM sleep, but our results do not suggest that colic infants would have abnormal autonomic reactivity to stimuli while asleep.