Table 2 Heart rate variability feature parameters of ECG

Time-domain

\(\stackrel{-}{\mathrm{RR}}\)

[ms]

The mean of RR intervals

 SDNN

[ms]

Standard deviation of normal to normal RR intervals

\(\stackrel{-}{\mathrm{HR}}\)

[1/min]

The mean heart rate

 SDHR

[1/min]

Standard deviation of instantaneous heart rate values

 MinHR

[beats/min]

Min heart rate per minute

 MaxHR

[beats/min]

Maximum heart rate per minute

 RMSSD

[ms]

The root mean square of successive RR interval differences

 NN50

[count]

Number of successive RR interval pairs that differ more than 50 ms

 pNN50

[%]

NN50 divided by the total number of all NN intervals

 HRV triangular index

–

The integral of the RR interval histogram divided by the height of the histogram

 TINN

[ms]

Baseline width of the NN interval histogram

Frequency-domain

 VLF power

[ms²]

Absolute power of VLF band

 LF power

[ms²]

Absolute power of LF band

 HF power

[ms²]

Absolute power of HF band

 LF/HF

–

Ratio between LF and HF band powers

 Total power (TP)

[ms²]

Total spectral power

 Normalized LFP

–

LF/(TP-VLF)

 Normalized HFP

–

HF/(TP-VLF)

Nonlinear

 SD1

[ms]

Poincaré plot standard deviation perpendicular the line of identity

 SD2

[ms]

Poincaré plot standard deviation along the line of identity

 SD2/SD1

[%]

Ratio of SD2 to SD1

 ApEn

–

Approximate entropy

 SampEn

–

Sample entropy

\({\alpha }_{1}\),\({\alpha }_{2}\)

–

Short-term and long-term fluctuations of detrended fluctuation analysis (DFA)