This article evaluates the suitability of low frequency (LF) heart rate variability (HRV) as an index of sympathetic cardiac control and the LF/high frequency (HF) ratio as an index of autonomic balance. It includes a comprehensive literature review and a reanalysis of some previous studies on autonomic cardiovascular regulation. The following sources of evidence are addressed: effects of manipulations affecting sympathetic and vagal activity on HRV, predictions of group differences in cardiac autonomic regulation from HRV, relationships between HRV and other cardiac parameters, and the theoretical and mathematical bases of the concept of autonomic balance. Available data challenge the interpretation of the LF and LF/HF ratio as indices of sympathetic cardiac control and autonomic balance, respectively, and suggest that the HRV power spectrum, including its LF component, is mainly determined by the parasympathetic system.

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The data suggest that autonomic cardiovascular regulation in FMS is impaired in terms of reduced sympathetic and parasympathetic influences, as well as baroreflex malfunctioning. Furthermore, autonomic cardiovascular adjustment to acute stress is blunted. The inverse association between BRS and pain severity reflects the well-documented pain inhibition through the baroreceptor system. On account of this and the reduced baroreflex function in FMS, one may assume deficient ascending pain inhibition arising from the cardiovascular system, which may contribute to hyperalgesia that is characteristic of the disorder.

Fibromyalgia syndrome (FMS) is a chronic disorder characterized by widespread and persistent musculoskeletal pain and other frequent symptoms such as fatigue, insomnia, morning stiffness, cognitive impairment, depression, and anxiety. FMS is also accompanied by different comorbidities like irritable bowel syndrome and chronic fatigue syndrome. Although some factors like negative events, stressful environments, or physical/emotional traumas may act as predisposing conditions, the etiology of FMS remains unknown. There is evidence of a high prevalence of psychiatric comorbidities in FMS (especially depression, anxiety, borderline personality, obsessive-compulsive personality, and post-traumatic stress disorder), which are associated with a worse clinical profile. There is also evidence of high levels of negative affect, neuroticism, perfectionism, stress, anger, and alexithymia in FMS patients. High harm avoidance together with high self-transcendence, low cooperativeness, and low self-directedness have been reported as temperament and character features in FMS patients, respectively. Additionally, FMS patients tend to have a negative self-image and body image perception, as well as low self-esteem and perceived self-efficacy. FMS reduces functioning in physical, psychological, and social spheres, and also has a negative impact on cognitive performance, personal relationships (including sexuality and parenting), work, and activities of daily life. In some cases, FMS patients show suicidal ideation, suicide attempts, and consummated suicide. FMS patients perceive the illness as a stigmatized and invisible disorder, and this negative perception hinders their ability to adapt to the disease. Psychological interventions may constitute a beneficial complement to pharmacological treatments in order to improve clinical symptoms and reduce the impact of FMS on health-related quality of life.

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This study investigated cognitive performance in fibromyalgia syndrome (FMS) and its association with cardiovascular and clinical parameters. Thirty-five patients with FMS and 29 matched healthy controls completed a neuropsychological test measuring attention and arithmetic processing. As possible factors underlying the expected cognitive impairment, clinical pain intensity, co-morbid depression and anxiety disorders, sleep complaints, medication use, as well as blood pressure parameters were investigated. The patients' test performance was substantially reduced, particularly in terms of lower speed of cognitive processing and restricted improvement of performance in the course of the task. While the extent of depression, anxiety, fatigue and sleep complaints was unrelated to test performance, better performance was observed in patients showing lower pain ratings and those using opiate medication. The data corroborate the presence of substantial cognitive impairment in FMS. While the experience of chronic pain is crucial in mediating the deficits, co-morbid depression, anxiety, fatigue and sleep complaints play only a subordinate role. In the control group, but not in the patients, blood pressure was inversely associated with mental performance. This finding is in line with the well known cognitive impairment in hypertension. The lack of this association in FMS confirms previous research showing aberrances in the interaction between blood pressure and central nervous function in the affected patients.

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