Table 3.
An overview of the heart rate variability (HRV) measures in frequency-domain and time-domain and their relationship to the function of the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS)
| HRV Parameter | Units | Description | Association to SNS and PNS function | Studies reported | |
|---|---|---|---|---|---|
| Frequency-domain parameter | HF power | ms2 | High-frequency power (between 0.15 and 0.4 Hz) (synchronous with respiration); Parasympathetic/vagal activation is estimated | PNS | Schultz et al.,[25] Takada et al.,[26] Bozkurt et al.,[27] Nahshoni et al.,[28] Royster et al.,[29] Suzuki et al.[30] |
| LF power | ms2 | Low-frequency power (between 0.04 and 0.15 Hz) extracted from RR interval time series power spectrum | SNS | Takada et al.,[26] Bozkurt et al.,[27] Nahshoni et al.,[28] Royster et al.[29] | |
| VLF power | ms2 | Very low-frequency power (between 0 and 0.04 Hz) extracted from RR interval time series power spectrum | Undefined | NR | |
| LF/HF | LF/HF power ratio | SNS vs. PNS | Takada et al.,[26] Bozkurt et al.,[27] Royster et al.,[29] Nahshoni et al.[31] | ||
| HF | n.u. | HF power in normalized units (n.u.) representing the relative power in proportion to total power (TP) minus VLF power: HF [n.u.] = HF power/(TP – VLF power) | PNS vs. SNS | Ebert et al.,[9] Nahshoni et al.[31] | |
| LF | n.u. | LF power in normalized units (n.u.) representing the relative power in proportion to total power (TP) minus VLF power: LF [n.u.] = LF power/(TP – VLF power) | SNS vs. PNS | Ebert et al.,[9] Nahshoni et al.[31] | |
| Time-domain parameters | SDNN | ms | The standard deviation of all normal RR intervals (normal-to-normal intervals, NN), demonstrating overall variability | PNS ↑, SNS | Ebert et al.,[9] Bozkurt et al.,[27] Karpyak et al.[32] |
| RMSDD | ms | Root mean square of successive differences between RR intervals, demonstrating beat-to-beat variation | PNS ↑ | Bozkurt et al.,[27] Royster et al.[29] | |
| pNN50 | % | The percentage of adjacent NN intervals that differ from each other by more than 50 ms | PNS ↑ | Bozkurt et al.,[27] Karpyak et al.[32] |
NR=not reported. RR intervals, interbeat intervals between all successive heartbeats; NN intervals, interbeat intervals between successive heartbeats with artifacts removed