Table 2.

Description of parameters calculated by frequency domain analysis. Parameters were calculated for heart rate and systolic and diastolic blood pressure.

Method	Parameter	Description
Frequency domain	ULF	Power (=variability) in “ultra low frequency” range (0–0.0033 Hz)
	VLF	Power (=variability) in “very low frequency” range (0.0033–0.04 Hz)
	LF	Power (=variability) in “low frequency” range (0.04–0.15 Hz)
	HF	Power (=variability) in “high frequency” range (0.15–0.4 Hz)
	XHF	Extended high frequency band from 0.15 to 0.6  Hz
	XF	Frequency band from 0.12 to 0.18  Hz
	P	Total power density spectra (variance of all NN intervals ≤0.4 Hz)
	LF/HF	Ratio of LF and HF
	LF/P	Ratio of LF and P
	HF/P	Ratio of HF and P
	XHF/PX	Ratio of XHF and the extended total power (variance of all NN intervals ≤0.6 Hz)
	VLF/P	Ratio of VLF and P
	ULF/P	Ratio of ULF and P
	(ULF + VLF + LF)/P	Ratio of (ULF + VLF + LF) and P
	(ULF + VLF)/P	Ratio of (ULF + VLF) and P
	UVLF	Sum of ULF, VLF, and LF (≤0.15 Hz)
	LFN	Normalized low frequency
	HFN	Normalized high frequency