HEART-RATE-VARIABILITY IN LOW-RISK PREMATURELY BORN INFANTS REACHING NORMAL TERM - A COMPARISON WITH FULL-TERM NEWBORNS

To investigate the influence of prematurity and postnatal age on the m aturation of the autonomic nervous system function, we analysed heart- rate and heart-rate variability in twelve prematurely born infants ( < 3 7 weeks gestational age) reaching the conceptional age of 37-41 wee ks. These neonates were compared with sixteen 37-41 week conceptional age newborns (< 10 days postnatal age). Heart-rate variability was ana lysed by spectral analysis of interbeat intervals using Short-Time Fou rier Transform. We found that during both active and quiet sleep, the durations of RR-intervals were shorter and the amplitude of heart-rate variability in different frequency bands was lower in prematures reac hing term than in newborns of the same conceptional age (P < 0.001). B etween-state comparison showed differences in both groups. In both gro ups, low-frequency heart-rate variability was higher in active sleep t han in quiet sleep. Between-state differences of RR-intervals and high -frequency heart-rate variability were present only in newborns (P < 0 .01). Discrimination between newborns and prematures reaching term, ba sed on RR-intervals and heart-rate variability, was correct in both sl eep states with errors between 7 to 16%. However, in both newborns and prematures reaching term, between-state discrimination showed less re liable results, especially for quiet sleep discrimination with 24% (in PRT) and 20% (in NB) of errors. Our results, especially information g iven by factor analysis, suggest that the differences between newborns and prematures reaching term, concerning RR-interval and heart-rate v ariability, may be related to a changed balance between the sympatheti c and parasympathetic nervous systems with a diminished parasympatheti c component of heart rate control in prematures reaching term, as comp ared to newborns.