[Metrological aspects of the spectral analysis of cardiac rhythm]

There are factors (presence of slow waves with the period that exceeds the recording duration, nonmultiplicity of the analysed oscillation periods to realisation), which do not allow reliable and reproducible estimations of the spectrum parameters in the slow area even in case of the stable patient's state. In case there are oscillations in the heart rhythm with periods comparable with the recording duration application of such a well known method like the elimination of polynominal trend to inhibit destabilizing effect of the factors is not effective enough. To increase the reliability and reproducibility in estimating heart rhythm wave pattern, its registration should be carried out only in the stable patient's condition long enough to cover several periods of the slowest analysed waves, that will limit the applications of the heart rhythm spectral analysis in clinical practice.