Linear and Nonlinear Heart Rate Variability Indexes in Clinical Practice

Table 2

Most used HRV measures. (modified from Heart Rate Variability: Standards of Measurement, Physiological Interpretation, and Clinical Use. Task Force of the European Society of Cardiology the North American Society of Pacing Electrophysiology. Circulation. 1996;93:1043–1065).

Time domain indexes	SDNN	Standard deviation of all NN intervals
	SDANN	Standard deviation of the averages of NN intervals in all 5-minute segments of the entire recording
	RMSSD	The square root of the mean of the sum of the squares of differences between adjacent NN intervals
	SDNN index	Mean of the standard deviations of all NN intervals for all 5-minute segments of the entire recording
	pNN50	NN50 count divided by the total number of all NN intervals
Frequecy domain indexes	Total power	Variance of all NN intervals (≤0.4 Hz)
	ULF	Power in the ULF range (≤0.003 Hz)
	VLF	Power in the VLF range (0.003–0.04 Hz)
	LF	Power in the LF range (0.04–0.15 Hz)
	HF	Power in the HF range (0.15–0.4 Hz)
	LF/HF	Ratio LF [ms^2]/HF[ms^2]