BACKGROUND: Heart period variability provides a measure of balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). Since the PNS develops during the final weeks of gestation, premature infants have an overriding SNS. Spectral power analysis of heart period variability reveals two main frequency regions, the low frequency region (LF) representing primarily SNS activity and the high frequency region (HF) representing PNS activity. OBJECTIVES: To identify the characteristics of heart period power in the LF and HF regions in very low birth weight (VLBW) infants in the neonatal intensive care unit across gestational age groups and between sleep and awake states. METHODS: Data were collected from 16 intubated and mechanically ventilated VLBW infants with respiratory disease. Using spectral analysis techniques, heart period power in the two main frequency regions was extracted. RESULTS: HF power did not improve with gestational age as expected. LF power did increase with age, albeit nonsignificantly. LF and HF power were not significantly different between awake and sleep states. CONCLUSIONS: The results of this preliminary study suggest that PNS tone does not improve with gestational age in VLBW infants with respiratory disease. The intensive care environment may stimulate a sympathetic response in these infants and disrupt normal PNS development. 2004 S. Karger AG, Basel.
BACKGROUND: Heart period variability provides a measure of balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). Since the PNS develops during the final weeks of gestation, premature infants have an overriding SNS. Spectral power analysis of heart period variability reveals two main frequency regions, the low frequency region (LF) representing primarily SNS activity and the high frequency region (HF) representing PNS activity. OBJECTIVES: To identify the characteristics of heart period power in the LF and HF regions in very low birth weight (VLBW) infants in the neonatal intensive care unit across gestational age groups and between sleep and awake states. METHODS: Data were collected from 16 intubated and mechanically ventilated VLBW infants with respiratory disease. Using spectral analysis techniques, heart period power in the two main frequency regions was extracted. RESULTS: HF power did not improve with gestational age as expected. LF power did increase with age, albeit nonsignificantly. LF and HF power were not significantly different between awake and sleep states. CONCLUSIONS: The results of this preliminary study suggest that PNS tone does not improve with gestational age in VLBW infants with respiratory disease. The intensive care environment may stimulate a sympathetic response in these infants and disrupt normal PNS development. 2004 S. Karger AG, Basel.