Autoregressive analysis of cardiac RR intervals in preterm and fullterm infants

For the purpose of obtaining information on the maturation process of the autonomic nervous system in pre- and full-term infants, polygraphs were recorded during sleep from a total of 52 appropriate-for-dates infants at a conceptional age of 28-41 weeks. The 104 RR interval time series was calculated by autoregressive (AR) and component analysis. Histograms of damping frequencies obtained were divided into two frequency bands: low frequency fluctuations (LF) of less the 0.1 cycle/beat (c/b) and high frequency fluctuations (HF) of more than 0.15 c/b. Total power and LF power decreased with increases in the conceptional age or postnatal age at a significance level of 0.01, respectively. In addition, the HF amount of bio-informing activity increased (P < 0.001) and the damping time of HF also increased (P < 0.01). From these results, it was speculated that the activity of the sympathetic system decreases with increases in conceptional or postnatal age. It was also speculated that increased regularity and oscillatory duration in HF might be caused by the development of the reciprocal response of respiration to heart rate variation.