Circulating Blood Volume

 

http://www.pediatricnetwork.org/medical/CFS/bell-commentary/circbloodvol99.htm

 

David S. Bell, MD, FAAP

Published in Lyndonville News, July 1999

Several questions have come up regarding the issue of circulating blood volume. I would like to outline my current feelings on this subject.

The first mention of this issue from the CFS perspective was in a paper by Dr. Streeten several years ago showing decreased circulating blood volume in orthostatic intolerance (1). We subsequently published a paper together about this in the JCFS (2). Other publications will be forthcoming, I hope.

Blood is made up of two components: fluid and red blood cells. There are other things there of course, but the volume of circulating blood in the body is mainly these two things. Two separate issues: total blood volume and anemia - they are quite different. The total volume is just that. It is the amount of blood in the whole body, both cells and fluid. It can be measured by draining all the blood out of the body into a bucket (not a good idea) or by the Cromium 51 study. Anemia is where the proportion of cells to fluid is abnormal, but the total volume of blood is normal. Anemia is routinely checked for in a CBC, but total circulating blood volume is not checked for, unless a Cromium 51 study is done.

In CFS, about 80% of patients will have decreased circulating blood volume. We have measured it in about fifty patients, and sometimes it is quite dramatic. A normal circulating blood volume is 71 ml/kg or roughly five quarts in a 180 pound person. Most of the persons we measure have about 50 ml/kg, with a symmetrical decrease in both the cells and the fluid (this is the reason that anemia is not found).

The current record in our office is 34 ml/kg. This means that the total blood volume is less than half of what it should be. A person with 45 ml/Kg would have a blood volume of 63.3% of normal (45 divided by 71). This degreased amount of blood circulating in the body is certainly able top cause problems.

If there is not enough blood in the system, circulation to certain organs, particularly the brain, could be impaired. If a normal person looses 40% of their blood volume in a car accident it is usually fatal. In CFS the loss is obviously not all at once, so it is not fatal. But it can cause problems in getting adequate oxygen to the brain, particularly if one is standing up.

It was my hope two years ago that this was the problem in CFS. Therefore, get the volume up to normal, and the symptoms would disappear. Unfortunately...well, you know the rest. It didn't work. In a number of patients we were able to correct the circulating volume using different agents. But they did not resolve their symptoms. Maybe some improvements, but it was not the answer. Also 20% of patients have a normal volume determination to start with.

Therefore the volume decreases in 80% of CFS patients must be secondary to something else, perhaps the autonomic nervous system. Correction of the primary problem would thus lead to automatic correction of the volume deficiency. In this regard I now see the volume problem is a possible help in diagnosis and important to understanding the illness, but certainly not the answer. It is like the immunological abnormalities - very real, and possibly helpful, but not the central issue.

It remains to be seen what the value of the circulating blood volume studies will be in the future. They may be important as a proof of organic abnormality in disability cases. It may be a diagnostic marker, and it may have treatment implications. I feel sure that it is related to the abnormality of vasopressin secretion, but that story will have to wait a month or so.

References:

  1. Streeten DHP, Anderson GH. Delayed orthostatic intolerance. Arch Intern Med. 1992; 152: 1066-72
  2. Streeten DHP, Bell DS. Circulating blood volume in chronic fatigue syndrome. JCFS. 1998. 4:3-12.

For readers who would like more information on NMH, Orthostatic Intolerance and circulating blood volume a few web sites are listed below:

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