Autonomic cardiovascular control and responses to experimental pain stimulation in fibromyalgia syndrome.

OBJECTIVE: This study involves a comprehensive investigation of autonomic cardiovascular regulation in fibromyalgia syndrome (FMS) at rest and during painful stimulation and its association with pain indices.
METHODS: In 35 patients and 29 healthy controls, electrocardiography, impedance cardiography, and finger continuous blood pressure measurements were conducted. For the purpose of experimental pain induction, a cold pressor test was applied.
RESULTS: FMS patients showed lower pain threshold and tolerance, as well as higher ratings of pain intensity and unpleasantness on visual analogue scales. Resting stroke volume, myocardial contractility, R-R interval, heart rate variability, and sensitivity of the cardiac baroreflex were reduced in the patients, and increases in stroke volume and myocardial contractility during cold pressor stimulation were less pronounced. In the whole sample as well as in the FMS group, baroreflex sensitivity was inversely associated with subjective pain intensity, and a higher number of baroreflex operations per unit of time predicted higher pain tolerance.
CONCLUSIONS: The data suggest impaired autonomic cardiovascular regulation in FMS in terms of reduced sympathetic and parasympathetic influences, as well as blunted sympathetic reactivity to acute stress. The association between baroreflex function and pain experience reflects the pain inhibition mediated by the baroreceptor system. Given the reduced baroreflex sensitivity in FMS, one may assume deficient ascending pain inhibition arising from the cardiovascular system, which may contribute to the exaggerated pain sensitivity of FMS.