The aim of the study was to investigate the cardiovascular correlates of simple relaxation and pain perception in chronic pain patients with high (highs) and low (lows) hypnotizability. ECG and skin blood flow (SBF) were monitored in 20 fibromyalgic (FM) and 20 healthy age-matched control women (Controls).

During simple relaxation, in FM the normalized Very Low Frequency (VLFn, < 0.04 Hz) and High Frequency component (HFn, 0.15-0.4 Hz) of heart rate variability (HRV) were lower and higher, respectively, than in Controls. SBF spectral analysis showed lower VLFn and higher HFn (0.15-0.4 Hz, respiratory induced) in highs. The Low Frequency component (LFn, 0.04-0.15 Hz) did not show significant differences in the HRV and SBF variability.

During suggestions for analgesia patients perceived lower pain intensity than during simple relaxation, but the reduction was significant only in highs; both highs and lows increased their RR and the HFn component of HRV, and decreased the LF/HF index. Among the SBF spectral components, LFn (myogenic component) increased.

In conclusion, fibromyalgia is associated with lower renin-angiotensin activity and higher parasympathetic tone; high hypnotizability is associated with lower neurogenic/endothelial-derived spectral components of flow motion; the suggestions for analgesia modulate heart rate and heart rate/flow motion variability independently of hypnotizability and subjective efficacy.