Table 1.
Set of Features used in the current study presenting the designation used across the document, the units of measurement, a description of the feature and the papers reporting that feature for the analysis of HRV.
| HRV Features Initials | Units | HRV Features Description | References |
|---|---|---|---|
| Time Domain | |||
| mNN | [ms] | mean of NN (or RR) intervals | [2] |
| SDNN | [ms] | standard deviation of NN (or RR) intervals | [2,10] |
| SDSD | [ms] | standard deviation of the differences between heartbeats | [2,10] |
| RMSSD | [ms] | the root mean square of the differences between heartbeats | [2,10] |
| NN50 | -- | number of consecutive RR intervals differing by more than 50 milliseconds | [2,10] |
| pNN50 | [%] | proportion of consecutive RR intervals differing by more than 50 milliseconds | [2,10] |
| Geometrical Domain | |||
| TI | -- | HRV Triangular Index–integral of the NN interval histogram divided by the height of the histogram | [2,10,25,26] |
| TINN | -- | Triangular Interpolation of RR (or NN interval) Histogram—baseline width of the NN interval histogram | [2,10,25,26] |
| SI | -- | Baevsky’s Stress Index | [27] |
| Non-Linear Domain | |||
| ApEn | -- | Approximate Entropy—measures the complexity or irregularity of the RR series | [28] |
| SD1 | [ms] | Standard Deviation of the Poincare plot perpendicular to the line of identity | [2,6] |
| SD2 | [ms] | Standard Deviation of the Poincare plot along the line of identity | [2,6] |
| PTM | -- | Point Transition Measure—quantifies the temporal variation at the point-to-point level of the Poincare plot | [6] |
| KFD | -- | Katz Fractal Dimension | [29] |
| HFD | -- | Higuchi Fractal Dimension | [30] |
| Frequency Domain | |||
| VLF | [ms2] | Very-Low-Frequency band power (≤0.04 Hz) | [2,10] |
| LF | [ms2] | Low-Frequency band power (0.04–0.15 Hz) | [2,10] |
| HF | [ms2] | High-Frequency band power (0.15–0.4 Hz) | [2,10] |
| VLFnu | n.u. | VLF power normalized | [2,10] |
| Lfnu | n.u. | LF power normalized | [2,10] |
| HFnu | n.u. | HF power normalized | [2,10] |
| VLFpeak | [ms2] | VLF power frequency peak | [2,10] |
| LFpeak | [ms2] | LF power frequency peak | [2,10] |
| HFpeak | [ms2] | HF power frequency peak | [2,10] |
| VLFpeak-nu | n.u. | VLF power frequency peak normalized | [2,10] |
| LFpeak-nu | n.u. | LF power frequency peak normalized | [2,10] |
| HFpeak-nu | n.u. | HF power frequency peak normalized | [2,10] |
| totPow | [ms2] | Total Power | [2,10] |
| Peak | [ms2] | Overall frequency power peak | [2,10] |
| LF/HF | -- | Ratio of LF and HF band powers | [2,10] |
| LFpeak/HFpeak | -- | Ratio of LF and HF band power frequency peak | [2,10] |