Nighttime (00:00–06:00) heart rate variability (HRV).
| Fibromyalgia, n = 13 | Control, n = 11 | p | |
|---|---|---|---|
| Longer-term HRV | |||
| Heart rate (beats per minute) | 73 ± 11 | 67 ± 9 | 0.160 |
| SDNN [SD of N-N intervals (ms)] | 80 ± 22 | 93 ± 21 | 0.141 |
| SDANN [SD of 5-min averaged N-N intervals (ms)] | 67 ± 21 | 47 ± 19 | 0.021 |
| Ln (ultra low frequency power) | 8.46 ± 0.60* | 7.75 ± 0.77 | 0.021 |
| Intermediate-term HRV | |||
| SDNNIDX [average of 5-min SDs of N-N intervals (ms)] | 58 ± 17 | 60 ± 19 | 0.849 |
| Ln (very low frequency power) | 7.49 ± 0.60* | 7.37 ± 0.50 | 0.596 |
| Ln (low frequency power) | 6.79 ± 0.73* | 6.68 ± 0.57 | 0.679 |
| Short-term HRV | |||
| pNN50 [percent of N-N intervals > 50 ms different from previous] | 11.4 ± 10.8 | 18.0 ± 19.2 | 0.304 |
| rMSSD [root mean square of successive differences of N-N intervals (ms)] | 35 ± 17 | 43 + 25 | 0.359 |
| Coefficient of variance (%) | 11.4 ± 3.7 | 8.7 ± 1.7 | 0.038 |
| Ln (high frequency power) | 5.82 ± 1.07* | 6.21 ± 0.91 | 0.360 |
| Ratio-based HRV | |||
| Normalized low frequency power (%) | 66 ± 9* | 54 ± 17 | 0.033 |
| Normalized high frequency power (%) | 27 ± 10* | 41 ± 17 | 0.025 |
| Low frequency/high frequency ratio | 3.9 ± 2.0* | 2.4 ± 2.1 | 0.121 |
| Nonlinear HRV | |||
| DFA1 | 1.27 ± 0.17* | 1.05 ± 0.28 | 0.033 |
| SD12 | 0.27 ± 0.08* | 0.38 ± 0.13 | 0.029 |
↵* N = 12 FM. Ln: natural log. N-N intervals: times between heartbeats 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 h. Very low frequency power: variance in heart rate explained by underlying cycles from once in 20 s to once in 5 min. Low frequency power: variance in heart rate explained by underlying cycles of 3–9 per min (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). DFA1: the short-term fractal scaling exponent, expressing the degree of randomness or correlation of 4–11 beat sequences. SD12: the Poincaré ratio, the ratio of the axes of an ellipse drawn to fit the scatterplot of each N-N interval vs the next.