- Last Updated: 02 December 2015 02 December 2015
Neurally-mediated hypotension in ME/CFS
Dr. Klimas gave a short description of this condition. Normally, when a person stands up much of the blood volume goes to the legs and feet. As a result, there is a very brief reduction of blood volume available to the heart; sensors in the heart respond by sending a sympathetic nerve signal to the brain calling for increased blood pressure and pulse. The brain sends the signal to provide increased blood flow, and within a couple of minutes, having obtained blood it needs, the heart should send a second message to the brain calling for a small parasympathetic response to reduce blood flow to prevent any overshooting or hypertensive response.
In ME/CFS, upon standing, everything happens properly until the final parasympathetic response. The parasympathetic response, instead of providing a small downward adjustment in blood pressure, is way overstated and you get a big blood pressure and pulse drop.
The blood pressure can go to 60/30 or under and the pulse to 40. Many doctors fail to diagnose this condition, because they ask if the patient actually has had instances of fainting. If the ME/CFS patient has been able to prevent actual fainting and answers no, then the doctor moves on. The doctor fails to ask if the patient has felt like fainting.
Blood volume and red blood cell mass
Similarly, Drs. Bell and Streeten found an intriguing set of abnormalities in their work on ME/CFS patients' blood volumes. They did sophisticated tests that tagged red blood cells to make a count of the entire number of RBCs in the body. At the same time, they measured the volume of blood plasma. Bell and Streeten found abnormal numbers both in plasma and RBCs.
If the number of red cells is much lower, then the cells have to try to deliver less oxygen much more quickly. This can result in tachycardia and other circulatory difficulties. If blood volume or plasma volume is low, then the blood goes to the feet and there is greater difficulty getting blood to the heart and head.
The kidneys control blood volume. They determine how much liquid goes out through the urine and how much stays in. The kidneys also make erythropoetin (EPO), a hormone that tells the bone marrow to make more red blood cells. The sympathetic nervous system is responsible for signaling the kidneys to retain or excrete liquid, thereby altering blood volume.
Dr. Klimas is doing a partially funded NIH study to determine if the sympathetic tone of kidneys is affected in ME/CFS, and if there is a therapeutic intervention She has commenced EPO clinical trials, by injection, to induce more red blood cell formation (in people with documented low RBC). She hopes the trials will show efficacy of the treatment.