Table 1.

HRV parameters and calculation methods.

HRV parameters	Calculation methods
Mean RR	Average of all normal-to-normal (NN) intervals
SDNN	Standard deviation of NN intervals (overall HRV)
RMSSD	Root mean square of successive NN differences (parasympathetic activity)
SDHR	Standard deviation of heart rate values
PNS index/SNS index	Composite indices reflecting parasympathetic and sympathetic activity
DCmod/ACmod	Derived using phase-rectified signal averaging (PRSA), representing deceleration and acceleration capacities of heart rate, respectively