Rhythmic structure of circaseptan series of heart rate variability in newborns

RHYTHMIC STRUCTURE OF CIRCASEPTAN SERIES OF HEART RATE VARIABILITY IN NEWBORNS. Narogan M. V. *, Syutkina E. V. **, Masalov A. V. ***. *Moscow Regional Scientific Research Clinical Institute, Moscow; **Scientific Center for Children’s Health, Russian Academy of Medical Sciences, Moscow; ***Lebedev Physical Institute, Russian Academy of Sciences, Moscow. INTRODUCTION. The idea to study the heart rate variability (HRV) has been originated from the concept of the circulatory system as an indicator of the adaptation reactions of the whole body [Parin V.V., Baevskii R.M., et all., 1967]. The cardiovascular system is characterized by the most rapid and fine responses to the regulatory effects of the autonomic nervous system (ANS). The development of methods for analyzing HRV had begun by Russian scientists - V.V. Parin and R.M. Baevskii. Spectral analysis of heart hate (HR) is one of the methods for evaluating the state of ANS. In the HR spectrum, two main frequency ranges are distinguished: high-frequency (HF) and low-frequency (LF) ones. It is believed that oscillations in the HF range are connected with respiratory waves and the activity of the parasympathetic nervous system. Oscillations in the LF range is connected with Mayer (vasomotor) waves. They are considered to be mediated predominantly by the sympathetic division of ANS. The LF-to-HF ratio is often used as an index of the sympathovagal balance. Almost every month, leading medical journals publish the results of HRV studies; quite a number of them deal with infants. However from the whole recordings, the researchers select only short segments (1- to 5-minites), which are subjected to spectral analysis. The aim of our work is to study the long rhythms (circadian, circaseptan, circasemiseptan) of the HF-, LF-power and LF-to-HF ratio in infants. PATIENTS AND METHODS. We studied 33 newborns, hospitalized in the intermediate unit for preterm infants of the Scientific Center for Children’s Health. They were predominantly preterm and had hypoxic cerebral pathology. Some of them also had respiratory disorders and were small for gestation age. The most part of the study was performed at infants’ age of 1 or 2 months. Initially we have studied HRV on the basis of long (about a week) registration of cardiointervals (CI). For this purpose we used the device Minilogger-2000, which is capable to record a high HR (up to 240 beats/min, which corresponds to a CI of 250 ms) and has adequate accuracy (1 ms). Obviously, the LF and HF ranges will have age-related distinctions connected with differences in the main physiological parameters: the HR and the respiratory rate. In infants, the LF and HF boundaries are not clearly delineated and differ in various works. We identified this boundaries as LF from 0.025 to 0.3 Hz and HF from 0.3 to ~1 - 1.5 Hz. The artifact-free CI series were subjected to spectral-temporal analysis by the least-square method. In the process, the spectrum was determined in a 36-s time window, which was shifted with 9-s steps. The spectral power was averaged to determine the total spectral power within a 3-min interval. 3-min segments of HF & LF spectral power were studied in order to find rhythmic structure in the range of 24 hours – 7 days. RESULTS. When we planned this work, we supposed to find circaseptan and/or circasemiseptan rhythms of HRV, as it is known, that these rhythms are expressed well in other physiological variables of newborns [Halberg F., Cornelissen G., et all., 1994]. However circadian rhythm dominated in all histograms – of LF, HF and LF-to-HF ratio. Circaseptan and circasemiseptan rhythms also were found but more rare then circadian. We do not find any dependence between the occurrence of circaseptan and/or circasemiseptan rhythms and gestational or postnatal age. Only one 4-month old infant had accurate LF and HF circaseptan rhythms. CONCLUSIONS. In HRV of newborn infants the circadian rhythm occurs more often than circaseptan and/or circasemiseptan rhythms. We did not find any dependence between the occurrence of circaseptan and/or circasemiseptan rhythms and the gestational or postnatal age of infants.