New research from Australia adds to a substantial body of evidence indicating autonomic nervous system imbalance plays a central role in causing the wide-ranging symptoms of chronic fatigue syndrome.
In the journal PLOS ONE investigators show for the first time that reduced heart rate variability (HRV) – or changes in heart beat timing – best predicts cognitive disturbances, including imparied concentration, mental focus and short-term memory commonly reported by people with chronic fatigue syndrome (CFS).
The autonomic nervous system (ANS) is responsible for maintaining balance and normal function within the body through interactions with other key systems such as the endocrine system and immune system. The hypothalamus in the brain is a key component of the ANS and can be looked upon as the conductor of the bodily orchestra - if the hypothalamus is giving incorrect instructions, dysfunction throughout the ANS, endcrine system, immune system and other bodily systems ensues. It has been thought for some time now that this is what is going on in CFS. Abnormal hormone levels, particularly low levels of the adrenal stress hormone cortisol, have long been seen in CFS patients and are a logical consequence of ANS dysfunction.
"We have studied autonomic function in CFS for some time and our findings clearly indicate a loss of integrity in stress-responsive neural and physiological systems in CFS. Patients with this condition are hyper-responsive to challenges arising both from within the body and from the environment," says lead researcher, Associate Professor Ute Vollmer-Conna of the University of New South Wales in Sydney, Australia.
"Even when they sleep, their stress-responsive neural systems are on high alert, signalling that it is not safe to relax. I think this condition may be understood by analogy to post-traumatic stress disorder, just that in CFS the original trauma is most likely a physiological, internal one, such as a severe infection."
CFS is typically preceeded by a flu-like viral illness that patients never fully recover from. Equally, a significant number of CFS patients report that environmental factors, for example exposure to chemicals such as pesticides, triggered their illness.
In a study of 30 patients with CFS and 40 healthy individuals, UNSW researchers recorded the heart beats of participants (via ECG) and analysed cardiac responses to cognitive challenges, and associations with mental performance outcomes.
The patients with CFS performed with similar accuracy, but they took significantly longer to complete the tests than people without the condition. They also had greater heart rate reactivity; low and unresponsive heart rate variability; and prolonged heart rate-recovery after the cognitive challenge.
Resting heart rate variability (an indicator of vagus nerve activity) was identified as the only significant predictor of cognitive outcomes, while current levels of fatigue and other symptoms did not relate to cognitive performance.
"This is the first demonstration of an association between reduced cardiac vagal tone and cognitive impairment in CFS. Our findings confirm previous reports of a significant loss of vagal modulation, which becomes particularly apparent when dealing with challenging tasks. The current results are consistent with the notion that CFS represents a 'system under stress'," Associate Professor Vollmer-Conna says.
The findings could lead to new ways to improve cognitive difficulties in people with CFS, including biofeedback assisted retraining of autonomic functioning, the researchers say.
Reference: Beaumont A Burton AR Lemon J Bennett BK Lloyd A Vollmer-Conna U (2012) Reduced Cardiac Vagal Modulation Impacts on Cognitive Performance in Chronic Fatigue Syndrome PLOS ONE 7(11): e49518