Effects of the lower frequency limit on determining high frequency power of heart rate fluctuations

Parasympathetic autonomie nervous system activity is reflected in the high frequency (HF) range of heart rate fluctuations. The proper selection of the limits of this HF frequency range is important for following parasympathetic activity under different physiologic or pathologic conditions. A low cut-off frequency of 0.15 Hz allows power from lower frequencies components which are not solely connected with the parasympathetic system to enter into calculations of HF activity. This error of HF power estimation causes, for instance, masking of increased true HF activity during sleep. A low cut-off frequency of 0.2 Hz remedies such problems while only rarely leading to errors due to peak HF power at frequencies lower than 0.2 Hz.