Hi, all.
Here's a repost of something I wrote about POTS a few months ago. I hope it will be helpful.
Rich
In my view, there are three things that occur in CFS that are likely contributors to POTS:
1. The total volume of blood in the body is often lower than normal. This likely results from a "mild" diabetes insipidus (not the same as diabetes mellitus) which is often present in CFS. This in turn is caused by lower than normal secretion of antidiuretic hormone (ADH) by the hypothalamus/pituitary. In my hypothesis, this is caused by glutathione depletion in these organs. The low ADH secretion causes the kidneys to dump too much water from the blood into the urine, and that lowers the total blood volume. People with diabetes insipidus have high 24-hour urine volumes (sometimes much higher than the normal average of 1.5 liters per day), and they usually have constant thirst. They drink a lot of fluids, but can't keep up with the loss of water into the urine, so they run at lower than normal total blood volume all the time. The osmolality (depends on concentrations of solutes, including the electrolytes) of the blood is higher than normal, and the osmolality (and specific gravity) of the urine is lower than normal.
The low total blood volume causes the venous return of blood to the heart to be lower than normal, and that lowers the stroke volume, since the heart can pump out only what it receives. The cardiac output (the product of the stroke volume and the heart rate) is particularly lowered when standing, because of the additional effect of gravity. Low cardiac output prompts the autonomic nervous system to speed up the heart rate in an effort to raise the cardiac output and deliver more blood when standing, and that constitutes POTS.
2. Most people who have CFS have dysfunction of the HPA (hypothalamus-pituitary-adrenal) axis. This causes the cortisol output to be abnormal, usually too high in the early part of the illness, and then dropping down to be too low later in the illness. This interacts with the secretion of adrenaline (epinephrine), and noradrenaline (norepinephrine). Among other things, these hormones control the operation of the heart and the circulatory system. This dysfunction may also contribute to POTS. In my hypothesis, this dysfunction is also due to glutathione depletion in the hypothalamus and pituitary.
3. Many people with CFS have diastolic dysfunction of the heart. This means that the main pumping chamber of the heart (the left ventricle) does not fill with enough blood during the diastolic phase of the heart's cycle, and that also limits how much blood is pumped out (stroke volume). A low stroke volume again prompts the autonomic nervous system to speed up the heart rate in order to raise the cardiac output. Diastolic dysfunction is caused by too low a rate of supply of ATP to the heart muscle cells by their mitochondria. In my hypothesis, this is caused by glutathione depletion in the heart.
The bottom line is that glutathione depletion can explain all of these aspects as well as many more aspects of CFS. In recent years, we have found that the glutathione depletion in CFS is linked to a dysfunction in the methylation cycle, and that lifting the partial block in the methylation cycle will restore glutathione and correct many of the aspects of CFS. If you want to read more about this, you can find information at
www.cfsresearch.org.