The role of cardiovascular activity in fibromyalgia and conditioned pain modulation.

Fibromyalgia (FM) is a chronic widespread pain condition of unknown origin. Reduced endogenous pain inhibition could be related to high pain sensitivity in FM. Associations between conditioned pain modulation (CPM) and cardiovascular responses to pain have been observed in healthy subjects (HS). Because reduced cardiovascular reactivity to various stressors has been reported in FM patients, we investigated relationships between CPM and cardiovascular response to the cold pressor test (CPT) in 22 FM patients and 25 HS. CPM was evaluated by comparing pain intensity produced by a 120-second heat test stimulus (HTS) before and after a CPT (2minutes, 12°C). The CPT, used to activate CPM, produced greater pain intensity in FM patients. Patients with FM had higher heart rates than HS at baseline and during CPT. Higher heart rate was related with higher pain intensity during the CPT. Blood pressure increments during CPT were weaker in the FM group. CPM was less effective in FM patients than in HS. Importantly, systolic blood pressure responses during CPT were positively related to CPM effectiveness, suggesting that reduced blood pressure response during the conditioning stimulus could be involved in CPM dysfunction in the FM group. Higher heart rate could be implicated in the greater sensitivity to cold pain in FM. Patients with FM have reduced blood pressure response to a painful CPT. Reduced cardiovascular reactivity to pain could have important involvement in diminished endogenous pain inhibition efficacy and FM pathophysiology.