Table I.

Panel of Measurements of the RR Interval and Various Derivations of the RR Interval

Time domain intervals

Average heart rate

Average RR interval (NN)

SD of the RR intervals over a 24‐hour period (SDNN)

SD of all 5‐minute mean RR intervals (SDANN)

Average SD of all 5‐minute RR intervals (ASDNN)

Percentage of RR intervals with >50 ms variation (pNN50)

Square root of mean squared differences of successive RR intervals (RMSSD)

Covariance of the RR intervals (CVNN)

Frequency domain indices

Total power spectrum (0–0.4 Hz)

High‐frequency power (HF, 0.015–0.4 Hz)

Low‐frequency power (LF, 0.04–0.15 Hz)

Very‐low‐frequency power (VLF, 0.003–0.04 Hz)

Ultra‐low‐frequency power (ULF, ≤0.003 Hz)