SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY IN SPONTANEOUSLY BREATHING VERY PRETERM INFANTS

The influence of maturation, sleep state and respiration on heart rate variability was studied in 16 spontaneously breathing preterm infants (<33 weeks). ECG, respiratory impedance curve and movements were reco rded four times a day, during the first three days of life. The power content of selected frequency bands of the R-R interval power spectrum , as well as respiratory frequency and breath amplitude oscillation fr equency, were calculated for 3-min periods. An increase in low frequen cy heart rate variability with gestational age was found. High-frequen cy variability increased during early postnatal life. Sleep state infl uenced very low-frequency heart rate variability. The amount of respir atory sinus arrhythmia and breath amplitude sinus arrhythmia was deter mined mainly by respiratory rate and breath amplitude oscillation freq uency, respectively. The influences of gestational and postnatal age o n heart rate variability might be due to an increase in sympathetic to ne before birth and a change in parasympathetic-sympathetic balance af ter birth. Respiration has an important influence on heart rate variab ility, even in very preterm infants.