https://pubmed.ncbi.nlm.nih.gov/23166694/ Alison Beaumont 1, Alexander R Burton, Jim Lemon, Barbara K Bennett, Andrew Lloyd, Uté Vollmer-Conna Free PMC article Abstract Background: Cognitive difficulties and autonomic dysfunction have been reported separately in patients with chronic fatigue syndrome (CFS). A role for heart rate variability (HRV) in cognitive flexibility has been demonstrated in healthy individuals, but this relationship has not as yet been examined in CFS. The objective of this study was to examine the relationship between HRV and cognitive performance in patients with CFS. Methods: Participants were 30 patients with CFS and 40 healthy controls; the groups were matched for age, sex, education, body mass index, and hours of moderate exercise/week. Questionnaires were used to obtain relevant medical and demographic information, and assess current symptoms and functional impairment. Electrocardiograms, perceived fatigue/effort and performance data were recorded during cognitive tasks. Between-group differences in autonomic reactivity and associations with cognitive performance were analysed. Results: Patients with CFS showed no deficits in performance accuracy, but were significantly slower than healthy controls. CFS was further characterized by low and unresponsive HRV; greater heart rate (HR) reactivity and prolonged HR-recovery after cognitive challenge. Fatigue levels, perceived effort and distress did not affect cognitive performance. HRV was consistently associated with performance indices and significantly predicted variance in cognitive outcomes. Conclusions: These findings reveal for the first time an association between reduced cardiac vagal tone and cognitive impairment in CFS and confirm previous reports of diminished vagal activity.
The problem with HRV as a measure is the underlying causes are very non-specific. Reduced fitness itself can explain the difference between patients and controls and reduced fitness is a likely consequence of greater severity of the underlying illness. Mere association is not enough to derive conclusions.
