The goal of this systematic literature review is to determine whether there are differences and similarities in heart rate variability (HRV) between adult patients with fibromyalgia (FM), chronic fatigue syndrome (CFS), and healthy pain-free control subjects.
To obtain relevant articles, PubMed and Web of Knowledge were searched for case-control studies. Selection of the literature was based on selection criteria ascertaining studies with adult human patient groups comparing HRV. Risk of bias and levels of evidence were determined.
Sixteen case-control studies were included, 10 comparing FM patients to controls and 6 comparing CFS patients to controls. Methodological quality was moderate to good. Both time domain and frequency domain measurements were used. The majority of the researchers observed lower HRV in FM patients compared to healthy control persons, as well as increased sympathetic activity and a blunted autonomic response to stressors. Resistance training improved HRV in FM patients. In CFS patients HRV was only reduced during sleep.
FM patients show more HRV aberrances and indices of increased sympathetic activity. Increased sympathetic activity is only present in CFS patients at night. Since direct comparisons are lacking and some confounders have to be taken into account, further research is warranted. The role of pain and causality can be subject of further research, as well as therapy studies directed to reduced HRV.