Background Heart rate has been used to measure infants’ physiological stability during skin-to-skin holding. Variability in heart period (interbeat interval), a more sensitive measure of autonomic nervous system tone, has not.

Objective To describe heart period variability in intubated very-low-birth-weight infants during incubator care and during maternal skin-to-skin holding.

Design/Methods An experimental, interrupted time series, crossover design was used; infants served as their own controls. Infants were randomly assigned to treatment order: 2 hours of intermittent skin-to-skin holding for 2 consecutive days followed by 2 days of incubator care or vice versa. The analog signal representing heart period was sampled and quantized at 5 Hz via a dedicated computer system in multiple 300-second epochs each day.

Results Fourteen infants with similar characteristics completed the protocol. The mean interbeat interval was 332 ms during skin-to-skin care and 368 ms during incubator care. Power within the low-and high-frequency regions of heart period was not significantly different between skin-to-skin holding and incubator care. Mean low-frequency power was 124.6 ms22 during skin-to-skin holding and ranged from 51.9 ms22 to 71.4 ms22 during all periods of incubator care. Mean high-frequency power was similar during skin-to-skin holding and incubator care (8.8 ms22 and 6.1 ms22). Infants of 32 to 34 weeks’ corrected gestational age had increased power in the low- and high-frequency regions.

Conclusions Heart period variability did not improve during skin-to-skin holding. Gestationally older infants had increased power in the low- and high-frequency regions, suggesting a maturing autonomic nervous system.

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