Table 1.
HRV metrics used in this study.
| Domain | HRV metric | Unit | Description |
|---|---|---|---|
| Time | AVNN | ms | Average normal-to-normal interval |
| SDNN | ms | Standard deviation of normal-to-normal interval | |
| SDSD | ms | Standard deviation of successive difference of normal-to-normal interval | |
| RMSSD | ms | Root mean square of successive difference of normal-to-normal interval | |
| pNN50 | % | Percentage of normal-to-normal interval exceeds 50 ms | |
| Frequency | TP | ms2 | Total frequency power |
| VLF | ms2 | Very low frequency power of HRV (≤ 0.04 Hz) | |
| LF | ms2 | Low frequency power of HRV (0.04-0.15 Hz) | |
| HF | ms2 | High frequency power of HRV (0.15-0.4 Hz) | |
| LF/HF | n.u. | Ratio LF/HF | |
| nLF | n.u. | LF power in normalized units | |
| LF/(Total Power–VLF) | |||
| nHF | n.u. | HF power in normalized units | |
| HF/(Total Power–VLF) | |||
| Non-linear | SD1 | ms | Standard deviation of points (QRSn, QRSn+1) perpendicular to the axis of line of identity |
| SD2 | ms | Standard deviation of points (QRSn, QRSn+1) along the axis of line of identity | |
| ApEn | n.u. | Approximate entropy or normal-to-normal interval |