aRR (s)

Average width of the RR interval

STD (s)

Standard deviation of all RR intervals

avHR (beats/minute)

Average of the instantaneous heart rate (HR)

sdHR (beats/minute)

Standard deviation of the instantaneous HR

RMSSD (s)

Root mean square of differences between adjacent RR intervals

NN50 (count)

Number of consecutive RR intervals differing by more than 50 ms

pNN50 (%)

Number and percentage of consecutive RR intervals differing by more than 50 ms

Triangular index

Total number of all RR intervals divided by the height of the histogram of intervals

TINN

Baseline width of a triangle fit into the RR interval histogram using a least squares

LF power (ms^{2})

Power in low frequency range 0.040.15 Hz

HF power (ms^{2})

Power in high frequency range 0.150.40 Hz

Total power (ms^{2})

Total power estimated from RR intervals

LF norm (n.u.)

LF power in normalized units: LF/(Total powerVLF) × 100

HF norm (n.u.)

HF power in normalized units: HF/(Total powerVLF) × 100

LF/HF

Ratio of LF power to HF power
