Table 1.
A summary of HRV indices according to their respective analysis domains.
| Analysis Domain | Sub-Domain | Acronym | Description |
|---|---|---|---|
| Time-Domain | Deviation-based approach | SDNN | Standard deviation of NN intervals |
| SDANN | Standard deviation of average NN intervals for each 5 min segment | ||
| SDNN Index | Mean of the standard deviations of NN intervals in 5 min segments | ||
| Difference-based approach | SDSD | Standard deviation of successive NN interval differences | |
| RMSSD | Root mean square of successive NN interval differences | ||
| pNN20 | Proportion of successive NN interval differences larger than 20 ms | ||
| pNN50 | Proportion of successive NN interval differences larger than 50 ms | ||
| Geometric approach | HTI | Integral of the density of the NN interval histogram divided by its height | |
| TTIN | Baseline width of the RR interval histogram | ||
| Frequency-domain | Absolute Power | ULF | Power spectrum in the frequency range of ≤0.003 Hz |
| VLF | Power spectrum in the frequency range of 0.0033–0.04 Hz | ||
| LF | Power spectrum in the frequency range of 0.04–0.15 Hz | ||
| HF | Power spectrum in the frequency range of 0.15–0.4 Hz | ||
| Normalized/Relative Power | LnHF | Natural logarithm of HF | |
| HFn | Normalized HF | ||
| LFn | Normalized LF | ||
| LF/HF | Ratio of LF to HF power | ||
| Time-frequency domain | Linear approach | STFT | Power spectrum estimation using short-term Fourier transform |
| WT | Power spectrum estimation using Wavelet transform | ||
| Quadratic approach | WVD | Power spectrum estimation using Wigner–-Ville distribution | |
| SWVD | Power spectrum estimation using Smoothed Wigner–Ville distribution | ||
| Non-linear domain | Poincaré Plot | SD1 | Poincaré plot standard deviation perpendicular the line of identity |
| SD2 | Poincaré plot standard deviation along the line of identity | ||
| SD1/SD2 | Ratio of SD1 to SD2 | ||
| Entropy | ApEn | Estimation of complexity using approximate entropy | |
| SampEn | Estimation of complexity using sample entropy | ||
| MSE | Estimation of complexity using multiscale entropy | ||
| Fractal Dimensions | DFA | Estimation of signal fluctuations using detrended fluctuation analysis | |
| CD | Estimation of minimum number of variables to define a dynamic model |