To investigate heart rate variability (HRV) in fibromyalgia (FM) patients and healthy controls (HCs) during different sleep stages, and to examine the association of HRV with pain and sleep quality.
Polysomnography was recorded from 23 female FM patients and 22 age- and sex-matched HCs. HRV was recorded from bedtime until awakening including the standard deviation of normal-to-normal intervals (SDNN), the root mean square successive difference (RMSSD), and the low (LF; 0.04-0.15 Hz) and high (HF; 0.15-0.4 Hz) frequency power. Subjective scores of neck/shoulder pain and sleep quality were obtained at bedtime and awakening.
Both patients and HCs showed high incidence of arousals per hour (FM: 16 ± 9.7; HCs: 17 ± 11). RMSSD was lower in patients than HCs during non-rapid eye movement (non-REM) stage 2 (N2) sleep (mean ± SD; 30 ± 12 ms vs. 42 ± 13 ms, p < 0.002) and during REM sleep (23 ± 11 ms vs. 37 ± 16 ms, p < 0.003). HRV did not differ between groups during N3 sleep (p > 0.19 for all comparisons). In patients, SDNN, RMSSD, and HF power showed modest positive correlations with sleep quality (HF power during N3 sleep showed the highest correlation; Spearman's ρ = 0.54) and modest negative correlations with neck/shoulder pain (RMSSD during N3 sleep showed the highest correlation with pain at bedtime; Spearman's ρ = -0.51).
RMSSD, indicative of parasympathetic predominance, is attenuated in FM patients compared to HCs during N2 sleep and REM sleep. This difference was not present for the HF component. HRV during sleep in FM patients is moderately and positively associated with sleep quality and moderately and negatively associated with neck/shoulder pain.