Table 1.
Common HRV measures.
| Units | Description | |
|---|---|---|
| Time domain analysis | ||
| NN interval | ms | Normal-to-normal intervals. |
| SDNN | ms | Standard deviation of all NN intervals reflecting the sum of symphatic and parasympathetic activity. |
| SDANN | ms | Standard deviation of the averages of NN intervals in all 5 min segments of the entire recording and correlates with VLF and ULF over a 24 h period. |
| RMSSD | ms | The square root of the mean of the sum of the squares of differences between adjacent NN intervals reflecting vagally-mediated changes in HRV. |
| pNN50 | % | Percentage of NN intervals differing by more than 50 ms in the entire recording reflecting vagally-mediated changes in HRV. |
| Frequency domain analysis | ||
| Total power | ms2 | Variance of all NN intervals |
| 5 min total power | ms2 | Variance of NN intervals over the temporal segment (Frequency range: ≤0.4 Hz). |
| ULF | ms2 | Power in the ultra-low frequency range (≤0.003 Hz) |
| VLF | ms2 | Power in very low frequency range (≤0.04 Hz) |
| LF | ms2 | Power in low frequency range (0.04–0.15 Hz), reflects both symphatic and (predominantly) parasympathetic activity |
| LF norm | n.u. | (LF/Total Power-VLF) × 100 |
| HF | ms2 | Power in high frequency range (0.15–0.4 Hz), reflects parasympathetic activity. |
| HF norm | n.u. | (HF/Total Power-VLF) × 100 |
| LF/HF | Ratio of LF and HF | |