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Linear time domain indicators of HRV
| Features | Description |
|---|---|
| SDNN | Standard deviation of NN intervals (beat-to-beat intervals) calculated over a 24-hour period. |
| RMSSD | Root mean square of successive difference (RMSSD) is the square root of the mean of the sum of the squares of the successive differences between adjacent NNs. |
| NN50 | The number of pairs of successive NNs that differ by more than 50 millisecond. |
| pNN50 | The ratio obtained of NN50 divided by the total number of NNs. |
