Table 5. Twenty-four-hour Heart Rate Variability (HRV).
N-N intervals: times between heart beats with normal morphology and correct beat onset time. Ultra low frequency power: variance in heart rate explained by underlying cycles from once in 5 min to once in 24 hours. Very low frequency power: variance in heart rate explained by underlying cycles from once in 20s to once in 5 min. Low frequency power: variance in heart rate explained by underlying cycles of 3–9 per minute (based on averages of 5-min determinations). High frequency power: variance in heart rate explained by underlying cycles respiratory frequencies (9–24/min), based on averaged 5 min determinations. Normalized high frequency power: the average proportion of variance in heart rate explained by low frequency power (based on averaged 5-min determinations). LF/HF ratio: the numerical ratio of low to high frequency power (based on average 5 min determinations)
| Fibromyalgia N=11 |
Control N=10 |
p-value | |
|---|---|---|---|
| Longer-term HRV | |||
| Heart rate (beats per minute) | 75 ± 8 | 74 ± 9 | 0.682 |
| SDNN [SD of N-N intervals (msec)] |
105 ± 22 | 119 ± 33 | 0.267 |
| SDANN [SD of 5-min averaged N-N intervals (msec)] |
86 ± 21 | 101 ± 32 | 0.209 |
| Ln (ultra low frequency power) |
8.91± 0.47 | 9.19 ± 0.64 | 0.274 |
| Intermediate-term HRV | |||
| SDNNIDX [Average of 5-min SDs of N-N intervals (msec)] |
57 ± 13 | 56 ± 14 | 0.209 |
| Ln (very low frequency power) |
7.37 ± 0.45 | 7.24 ± 0.43 | 0.523 |
| Ln (low frequency power) | 6.76 ± 0.38 | 6.53 ± 0.36 | 0.182 |
| Short-term HRV | |||
| pNN50 [Percent of N-N intervals >50 msec different from previous] |
9.3 ± 8.8 | 14.7 ± 13.7 | 0.343 |
| rMSSD [Root mean square of successive differences of N-N intervals (msec)] |
32 ± 12 | 38 ± 19 | 0.343 |
| CV [Coefficient of variance (%)] |
13.1 ± 2.7 | 14.3 ± 3.3 | 0.348 |
| Ln (high frequency power) | 5.54 ± 0.78 | 5.97 ± 0.78 | 0.223 |
| Ratio-based HRV | |||
| Normalized low frequency power (%) |
70.4 ± 9.1 | 56.6 ± 10.3 | 0.004 |
| Normalized high frequency power (%) |
22.9 ± 9.1 | 35.0 ± 10.1 | 0.009 |
| Low frequency / high frequency ratio |
4.8 ± 2.3 | 2.7 ± 1.33 | 0.019 |
| Non-linear HRV | |||
| DFA1 | 1.31 ± 0.16 | 1.11 ± 0.18 | 0.016 |
| SD12 | 0.26 ± 0.06 | 0.32 ± 0.09 | 0.098 |
SD = standard deviation; Ln = natural log