Method | Measure of variability | Calculation of variable | Physiological mechanism |
---|---|---|---|
Time-domain methods | |||
Statistical | RMSSD | Root mean square of successive differences of NN intervals | Short-term components of HRV, vagal modulation |
SDNN | Standard deviation of the of all NN intervals | Overall HRV, cyclic components responsible for HRV | |
SDANN | Standard deviation of the averages of NN intervals in all 5-min segments of the entire recording (only for nocturnal HRV) | Long-term components of HRV | |
Frequency domain methods | |||
Lomb-Scargle Periodogram and Fast Fourier transformation | TP | Total power: power density spectrum in the frequency range of 0.00001 to 0.4 Hz [ms2] | Overall HRV |
LF | Low-frequency power: power density spectrum in the frequency range of 0.04 to 0.15 Hz [ms2] | Sympathetic and vagal activity, baroreflex activity (vasomotor tone) | |
HF | High-frequency power: power density spectrum in the frequency range of 0.15 to 0.40 Hz [ms2] | Vagal modulation | |
LF/HF | Ratio LF [ms2]/HF [ms2] | Sympathetic and vagal modulation |