THE DYNAMIC-RANGE OF NEONATAL HEART-RATE-VARIABILITY

Introduction: Although it is generally appreciated that heart rate var iability is low during severe illness, the extent, time course, and ma thematical characteristics of heart rate variability during transition s between health and illness have not been systematically examined. Th e purpose of this study was to analyze heart rate variability in newbo rn infants during a rapid recovery from severe respiratory and circula tory failure. Methods and Results: From prolonged ECG recordings, we e valuated heart rate variability in the time domain (mean, relative cha nge, and coefficient of variation of RR intervals),in the frequency do main(using power spectra of the time series of RR intervals), and usin g a neural network. Qualitatively, RR interval plots showed little hea rt rate variability during severe illness but became ''noisier'' durin g recovery. Quantitatively, recovery was marked by twofold to threefol d increases in time-domain parameters, by eightfold increases in frequ ency-domain parameters, and by more than 20-fold increases in a neural network measure. Time-domain and frequency-domain measures were corre lated, but not strongly. Heart rate variability reached stable levels by 4 to 5 days. Heart rate did not change dramatically. Conclusion: Re covery from severe neonatal illness is accompanied by large and rapid increases in heart rate variability, but not by large changes in heart rate. This increase can be effectively assessed in the time domain, i n the frequency domain, and by using a neural network.