Power Spectrum Analysis of Heart Rate Variability in Full-Term and Preterm Neonates

Objective: Prematurely born infants have been believed to be neurologically less mature than full-term neonates. The purpose of this study was to investigate the regulation and maturation of autonomic nervous systems, in both full-term and preterm neonates of different conceptional ages.Methods: One hundred and thirteen infants, both clinically and neurologically healthy and with conceptional ages of between 33 and 42 weeks, were enrolled in the study. Power spectrum analyses of heart rate variability were performed under standard conditions when the subjects were in a sleeping state. Results: Conceptional age did exert a significant influence over heart rate variability. There was a steady increase in total power and in the power of low frequency and high frequency components, along with a progressive decline of low frequency/high frequency ratio, as the conceptional age advanced. Infants of more than 36 weeks conceptional age demonstrated a significantly greater activity of autonomic nervous system than the younger group. However, the maturation of sympathovagal balance needed to take two more weeks with a low frequency/high frequency ratio cut-off age occurring at 38 weeks conceptional age. Gender and postnatal days at the time of the study did not exert a significant impact on the recordings. Conclusions: The function of autonomic nervous systems in preterm neonates was underdeveloped as compared with full-term neonates. This might account for the vulnerability to stress in this population. Every possible precaution should be taken to avoid jeopardizing their fragile lives, and continuous monitoring of vital signs during medical procedures should be mandatory in order to recognize major stress signs as early as possible.