  Factor structure of heart rate periodogram has been detected with factor
analysis. The results showed that there are at least four periodical phenomena
of HRV. Two of them have not been discovered and physiologically explained yet.
Their frequency ranges are 0.21 to 0.31 1/beat with the peak at 0.26 1/beat and
0.25 to 0.5 1/beat with the peak 0.35 1/beat. Despite of differences of the
peak frequencies the frequency rages of the factors are overlapped. Therefore,
power of spectral density within any frequency range could not be a measure of
a modulating physiological mechanism activity.
