A study that was published in Autonomic Neuroscience has found that an increased heart rate variability in CFS patients was also present during sleep, suggesting an ongoing state of sympathetic autonomic dysfunction.
The autonomic nervous system (ANS) is the part of the nervous system that controls involuntary bodily functions such as heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils and urinary secretion. Heart rate, blood pressure and breathing, among other things, are part of the sympathetic ANS.
Disorders of the ANS share many clinical features of CFS and are present in many people with the illness. Several studies have found differences in heart rate and heart rate variability in CFS cases. All of these studies, however, were conducted while subjects were awake and usually performing some type of challenge such as treadmill activity, head-up tilt test or forced/paced breathing. While these studies shed light on valuable elements of CFS pathophysiology, the role of the induced stress response, anxiety and other environmental conditions cannot be completely ruled out as contributing to altered ANS function.
Researchers Roumiana Boneva and colleagues from the CDC, the Department of Neurology at Emory University and the Department of Psychiatry and Behavioral Sciences at Emory University hypothesized that some of the ANS dysfunctions observed in CFSparticularly increased heart rate and decreased heart rate variabilitymight reflect an ongoing perturbation in autonomic function that would persist during sleep. They explored their hypothesis by studying 43 people with CFS, 61 people with medically-unexplained fatigue but not enough other symptoms to diagnose CFS and 60 healthy control subjects. All subjects were part of a massive study referred to as “Wichita Clinical.”
The heart rate of all study participants was monitored overnight, and levels of the adrenal hormones norepinephrine and aldosterone were also measured. Compared to the control subjects, the study participants with CFS had significantly higher mean heart rate (71.4 beats per minute vs. 64.8 beats for minute in control subjects) and reduced heart rate variability. CFS patients also had significantly lower plasma aldosterone and tended to have higher plasma norepinephrine levels. Limitation in moderate physical activity was strongly associated with the increased heart rate and decreased variability in the CFS patients. Nevertheless, among 42 study subjects with similar physical activity limitations, the subjects with CFS still displayed higher heart rate than the respective controls, suggesting that reduced physical activity could not fully explain the CFS-associated differences in ANS function.
The researchers conclude that the observation of heart rate and variability differences observed during sleep, coupled with higher baseline plasma norepinephrine and lower aldosterone, suggest a state of ANS dysfunction with perturbed neuroendocrine activity.