Measurement of heart rate variability in early neonates just after birth

Electrocardiographic (ECG) and respiratory movement waveform measurements were conducted in 15 early neonates from 30 minutes until 5 hours after birth, using an ECG measurement system that was developed to avoid discomfort to the subjects during the measurements. After calculation of the power spectral density (PSD) and the first-joint interval histogram using R-R intervals, the mean values of the PSD were calculated in the following low-frequency (LF) and high-frequency bands (HF); 0.04 to 0.15 Hz (LF), and above 0.15 Hz (HF). At one hour after birth in the neonates, the first-joint R-R interval histogram was concentrated focused temporarily on one spot, and the mean values of the PSD in the LF and HF band were less than that calculated at 30 minutes after birth. A slope of the 1/fⁿ fluctuations of the PSD close to a horizontal line. Later, with the passage of time, the mean values of the PSD and the slope of the 1/fⁿ fluctuations increased gradually. These results suggest that the heart rhythm becomes regular, when the actions of the autonomic nervous system on the heart decrease just after birth.