Blunted short-term autonomic cardiovascular reactivity to orthostatic and clinostatic challenges in fibromyalgia as an indicator of the severity of chronic pain.

Fibromyalgia is a long-term pain disorder that has been related to autonomic dysfunctions and reduced cardiovascular reactivity. We aimed to assess the dynamic short-term cardiovascular responses to postural changes in fibromyalgia. Thirty-eight women with fibromyalgia and thirty-six healthy women underwent the "Chronic Pain Autonomic Stress Test". Electrocardiogram, blood pressure and impedance cardiography were continuously recorded during active standing and lying down. Second-by-second values were derived over the first 30 s of each posture. Lower reactivity during the beginning of each position was observed in fibromyalgia sufferers compared to healthy women, with smaller responses seen during stand up in heart rate, blood pressure, cardiac output, total peripheral resistance, and pre-ejection period, and smaller changes during lying down in heart rate, cardiac output and total peripheral resistance. The magnitude of the autonomic adjustments to postural changes was inversely associated with the severity of clinical pain. These findings indicate an early impaired autonomic cardiovascular response to orthostatic and clinostatic challenges in fibromyalgia, suggesting less autonomic flexibility and adaptability to situational demands and challenges. Short-term second-by-second cardiovascular measures may be useful in the clinical assessment of fibromyalgia.