DEVELOPMENT OF HEART-RATE POWER SPECTRA REVEALS NEONATAL PECULIARITIES OF CARDIORESPIRATORY CONTROL

Postnatal adaptation should be associated with changes in cardiac rhyt hmic behavior. To examine the development of heart rate variability, i nstantaneous heart rate (IHR) and the corresponding breathing signals of 16 healthy infants were analyzed. This was pursued by use of fast F ourier transformation beginning with the Ist day until the 6th mo of l ife. Power in the low-frequency range (LF, 0.02-0.2 Hz) and high-frequ ency range (HF, 0.2-1.5 Hz), total power (TP), the quotient LF/HF, and the frequency of the peak in LF and HF (LFF and HFF, respectively) we re derived from the IHR spectrum. The peak frequency in HF (RF) was de tected in the respiratory spectrum. Power and frequency of IHR rhythms undergo a marked development. TP, LF, and HF are lowest from the end of the Ist mo until the 2nd mo. LF predominates over HF, with LF/HF re aching its peak during 1- to 2-mo period. HF, recording respiratory re lated rhythms, is negatively correlated with the breathing rate (BR). HFF and RF both show an increasing tendency during the Ist mo followed by a decrease down to the 6th mo. However, HFF is lower than RF if BR is high, mainly during the first 2 mo. The distinct changes in BR and its important influence on the IHR spectrum underscore the importance of monitoring respiration as a further measure in the diagnosis of in fants. LFF is on average between 0.075 and 0.095 Hz, exhibiting an irr egular course with minimum at the 10th, 21st-28th, and 90th day being apparent. The developmental pattern of LFF may be interpreted in terms of the maturation of the nervous system involved in the generation of circulatory rhythms.