Cardiovascular and blood pressure irregularities

Autonomic nervous system (ANS) dysfunction can present as neurally-mediated hypotension (NMH) or orthostatic intolerance (OI), but there are several other related conditions that fall into this category. ANS-driven disorders are moderately common in people with ME/CFS and FM, including children and youth with ME/CFS, but are not limited to these illnesses.

Basically, one's blood pressure will have an abnormal response to change of position (while standing) and the cardiovascular system will have to work much harder to maintain blood pressure and blood flow to the brain. Florinef (fludrocortisone) was one of the first treatments used to treat NMH by helping the body retain salt. 

Over time, it was found to lose its effectiveness because of potassium depletion and because it was not felt to be a very beneficial treatment. Other treatments might include medications to increase blood volume, work on vasoconstriction, or stimulate release of certain neurotransmitters.

Cardiac involvement

Mitral valve prolapse (MVP), low cardiac output, and a distinct cardiac disorder called "diastolic cardiomyopathy" has been found in ME/CFS by one of the leading doctors, Dr. Paul Cheney, who has followed patients with this illness over the past two decades. "Diastolic cardiomyopathy" refers to the heart muscle's failure to relax and to not allow proper filling. It was noticed in most patients (though not all) with ME/CFS. This problem is undergoing more research and there no specific treatment recommendations at this time.

Studies by Dr. Lerner at the University of Michigan documented intermittent tachycardia in a very high percentage of 51 ME/CFS patients (1988 CDC definition for CFS). The tachycardia was accompanied by T-wave abnormalities as measured by 24-hour Holter monitoring.

The studies found that 12 lead standard ECGs and 2-D echocardiograms do not generally show these cardiac abnormalities in ME/CFS. It is common for such abnormalities to be misdiagnosed as anxiety attacks, and thus of psychiatric origin. Instead, in Dr. Lerner's patients  they seemed to be the result of viral infection.