Table 2.

Definition of heart rate (HR) and heart rate variability (HRV) parameters.

Parameter	Definition
HR	Heart rate, bpm
AVNN	Mean beat-to-beat intervals, ms
SDNN	Standard deviation of beat-to-beat intervals, ms
RMSSD	Square root of the mean squared difference of successive RRs or inter-beat intervals, ms
pNN50	Percentage of successive RR intervals that differ by more than 50 ms, %
LF	Peak frequency of the low-frequency band (0.04–0.15 Hz)
HF	Peak frequency of the high-frequency band (0.15–0.40 Hz)
LF/HF	Ratio of LF-to-HF