Table 3.
Expansion and definition of HRV measurement acronyms.
| Measurement | Units | Expansion | Application | Interpretation |
|---|---|---|---|---|
| RMSSD | ms | Root-mean square of successive differences | Primary measurement for short-term vagally mediated changes (2) | Time-Domain Measurements generally increase with increased aerobic capacity (2, 47) |
| pNN20 | % | Percentage of adjacent intervals that differ by more than 20 ms | Assessment of vagal activity (2) Thresholds of ~6.8% or lower for disease states have been posited (48, 49) |
|
| pNN50 | % | Percentage of adjacent intervals that differ by more than 50 ms | ||
| AVNN | ms | Average value N-N; mean interbeat interval | Sensitive to changes in Psychological stress (50) | |
| SDNN (SDRR) | Ms | Standard deviation of all interbeat intervals during the sample period | Most widely acceptable HRV measurement for assessing cardiac risk (24-h recording only) (2) | |
| VLF | ms2 | Very-Low Frequency Band power (0.0033-0.04 Hz) | Intrinsically generated by the heart (2) Modulated by sympathetic activity (2) |
Low VLF power has been associated with cardiac death, PTSD and inflammation (2, 51) |
| LF | ms2 | Low Frequency Band power (0.04-0.15 Hz) | Represents baroreceptor activity during resting measurements (2) | Can be used to estimate vagal tone (2, 52) |
| LnLF | nu | Natural log of LF | Relative frequency band measurement to total power (53) | |
| HF | ms2 | High Frequency Band power (0.15-0.4 Hz) | Parasympathetic and respiratory activity (2) | Low HF values are associated with high stress (50) Correlated with RMSSD (2) |
| LnHF | nu | Natural log of HF | Relative frequency band measurement to total power (53) | |
| LF/HF | % | Ratio of LF to HF power | For resting seated measurements, likely measures PNS and baroreceptor activity (2) | Highly dependent on measurement conditions (2) |
| TP | ms2 | Total Spectral power | Useful for determining relative power measurements (2) | Broad estimate of total autonomic activity (2) |
| SD1 | ms | Standard Deviation from y-axis on Poincare plot | Nonlinear measurement, useful for short-term analysis without trend sensitivity (2) | Predicts RMSSD, pNN50, SDNN, and power in the LF and HF bands, and total power during 5 min recordings (2, 52) |
| SD2 | ms | Standard Deviation from x-axis on Poincare plot | Nonlinear measurement, useful for long-term analysis without trend sensitivity (2) | Correlates with LF power (2) |
| SampEn | – | Sample entropy or approximate entropy | Quantification of the unpredictability of a time series (2) | Useful for short recordings which may have noise (2) |
| Alpha1 | – | Short-term detrended fluctuation analysis Extracts the correlations between successive RR intervals over different time scales |
Reflects baroreflex activity (2) | Useful when longer recordings are not available (2) |