Table 1. Summary of proposed HRV analysis parameters.

Parameter	Unit	Description	References
Time-domain analyses: statistical methods
Mean RR	ms	The mean of RR intervals	[5]
SDNN	ms	Standard deviation of RR intervals	[5]
RMSSD	ms	Square root of the mean squared differences between successive RR intervals	[5]
NN50	count	Number of successive RR interval pairs that differ more than 50 ms	[5]
pNN50	%	NN50 divided by the total number of RR intervals	[5]
Time-domain analyses: geometrical methods
HRV triangular index	-	The integral of the RR interval histogram divided by the height of the histogram	[5]
TINN	ms	Baseline width of the RR interval histogram	[5]
Frequency-domain analyses
VLF, LF, HF power	ms2	Absolute powers of very low frequency band (0-0.04 Hz), low frequency band (0.04-0.15 Hz), and high frequency band (0.15-0.4 Hz), respectively	[5]
LF/HF ratio	-	Ratio between LF and HF band power	[5]
Nonlinear analyses: Poincaré plot
SD1, SD2	ms	Short-term and long-term variability standard deviation, respectively	[9,10]
Nonlinear analyses: correlation dimension
ApEn(0.2), ApEn(rmax), ApEn(rchon)	-	Approximate entropy where the tolerance value r is chosen to be r=0.2×SDNN, in the interval [0.1×SDNN, 0.9×SDNN] which maximizes ApEn, and computed according to the following formula proposed by Chon[12], respectively	[11,12]
SampEn	-	Sample entropy	[11]
Nonlinear analyses: correlation dimension
D2	-	Correlation dimension	[13]
Nonlinear analyses: detrended fluctuation analyses
α1, α2	-	Short-term and long-term fluctuations, respectively	[14.15]
Nonlinear analyses: recurrence plot
lmean	beats	Mean line length of diagonal lines	[16-18]
lmax	beats	Maximum line length of diagonal lines	[16-18]
REC	%	Recurrence rate (percentage of recurrence points)	[16-18]
DET	%	Determinism (percentage of recurrence points which form diagonal lines)	[16-18]
ShEn	-	Shannon entropy of diagonal line lengths’ probability distribution	[16-18]