By Suzanne Vernon, PhD, Scientific Director
Many people with CFS experience symptoms of postural orthostatic tachycardia syndrome or POTS, a form of orthostatic intolerance (OI). POTS is defined by an increase in heart rate of more than 30 beats per minute after changing position from lying down face-up to an upright or standing position, or a heart rate greater than 120 beats per minute within 10 minutes of becoming upright. The symptoms of POTS include
- exercise intolerance
It is estimated that as many as 70% of people with CFS also have POTS. The cause of POTS is not known, but the mechanisms of POTS are being deciphered. The American Journal of Physiology – Heart and Circulatory Physiology published a paper by Dr. Anthony J. Ocon titled, “Upright cerebral blood flow and cerebral autoregulation in normocapnic postural tachycardia syndrome.” Ocon works with Drs. Marvin Medow and Julian Stewart at the Center for Hypotension at New York Medical College. This important paper, together with the paper by Dr. Barry Hurwitz (below), provides provocative evidence for disturbances in circulatory regulation that decreases the flow of blood to the brain.
POTS occurs more frequently in younger people. This study included nine 15-29 year-old POTS subjects and seven healthy matched controls. All participants were subjected to head-upright tilt table testing (HUT). Measurements taken while lying down and during HUT included beat-to-beat blood pressure, heart rate using echocardiography, ETCO2 measured with a nasal cannula connected to a capnograph, respirations and cerebral blood flow velocity using a transcranial Doppler. The investigators found that during HUT, POTS subjects had significantly increased heart rate and significantly decreased cerebral blood flow velocity (speed and direction). The cerebral blood flow velocity was 19% decreased for POTS patients compared to 10% decreased for controls. By analyzing several blood flow parameters, the investigators were able to determine that both dynamic and static autoregulation of cerebral blood flow was less effective in POTS patients compared with control subjects during head-upright tilt. They conclude that substantially lowered cerebral blood flow occurs 50% of the time in POTS compared to controls when upright and that this can impair cerebral perfusion (nutrient delivery by the blood) and neurocognitive function.
The findings of low blood volume and slow blood flow help to explain the symptoms, but can these findings be used to improve treatment? This paper suggests therapies that increase arterial pressure may also increase cerebral blood flow velocity, possibly alleviating cognitive impairment. Treatment based on demonstrated mechanistic perturbations may also help to identify causes of POTS and CFS – a reverse engineering approach, if you will. This paper is an exciting demonstration of how combining powerful technology such as transcranial Doppler with sophisticated analytical approaches can begin to connect the dots to help us decipher complex conditions like POTS and CFS.
Ocon AJ, Medow MS, Taneja I, Clark D, Stewart JM. Decreased Upright Cerebral Blood Flow and Cerebral Autoregulation in Normocapnic Postural Tachycardia Syndrome. Am J Physiol Heart Circ Physiol. 2009 Jun 5. Online ahead of print publication.
Less Than Five Quarts?
Each of us has five quarts of blood that flows through a network of vessels to nourish every cell and every organ of our bodies. Blood is essential for life. Blood is the fluid that transports nutrients and oxygen throughout the body, as well as transports wastes out of cells. Blood maintains the body at a constant temperature; blood transports signals and chemicals for healthy body function and blood provides the readily mobilized immune cell force to fight infection.
The journal Clinical Science (London) has just published a paper by Barry E. Hurwitz, PhD, and colleagues from the University of Miami titled, “Chronic fatigue syndrome: illness severity, sedentary lifestyle, blood volume and evidence of diminished cardiac function.” Julian M. Stewart of New York Medical College provided comment on this important paper in this same journal issue. Stewart is a well-respected and published physiologist and I would like to share his summary and comments on this paper. First, Stewart states that the results of this paper “clearly demonstrated reduced stroke volume and cardiac output in severely afflicted patients with CFS, which is primarily attributable to a measurable reduction in blood volume.” He goes on to state that, “There is no controverting these data, which demonstrate decreased blood volume in a subset of CFS patients effectively reducing venous return to the heart, diastolic cardiac volume, and cardiac output. These data do not imply heart disease but rather point to circulatory impairment.” Stewart summarizes this paper writing, “the authors have importantly and clearly demonstrated a reduction in blood volume, both in plasma and in red cell mass that produces a reduction in cardiac filling via reduced venous return even when measured in the supine (lying down, face up) position”.
This study compared blood volume and cardiac function on the following groups: “severe CFS” defined as patients reporting 7 of 10 symptoms as moderate to severe according to the 1988 CFS case definition; “non-severe CFS” defined as patients meeting 1988 CFS case definition but without as many and as severe of symptoms; and “sedentary and non-sedentary controls.” These non-CFS subjects are an important control group since changes in blood volume and cardiac output can occur with inactivity. All subjects underwent a blood volume test, resting seated and supine blood pressure, cardiac function and structure testing using echocardiograms and graded exercise to obtain aerobic capacity. The main results of the study were
- lower cardiac index due to a decrement in stroke index;
- cardiac contractility index deficit; and,
- total blood volume deficit.
It should be noted that many of this study’s findings have been reported by other investigators. The authors note that even though the decrement in cardiac index was moderate and within normal ranges. This deficit could have physiologic relevance under conditions of physical and mental challenge (possibly explaining the post-exertional malaise of CFS).
How much less than five quarts was found in CFS patients? Five quarts is 4.7 liters. The severe CFS group had an average of 4.1 liters of blood compared to 4.6 liters in the sedentary controls. Even the non-severe CFS group had less blood volume (4.4 liters) than the sedentary controls. Low blood volume can be seen in a number of diseases including Addison’s disease, diabetes, and certain neurological disorders including Parkinson’s disease. This fact makes it plausible that low blood volume is an effect rather than a cause of CFS. Still, this important objective and quantitative study provides strong evidence of the biologic underpinnings of CFS and provides important clues to focus further research for possible causes.
Hurwitz BE, Coryell VT, Parker M, Martin P, Laperriere A, Klimas NG, Sfakianakis GN, Bilsker MS. Chronic fatigue syndrome: illness severity, sedentary lifestyle, blood volume and evidence of diminished cardiac function. Clin Sci (Lond). 2009 May 26. [Epub ahead of print]
Stewart JM. Chronic fatigue syndrome: comments on deconditioning, blood volume, and resulting cardiac function. Clin Sci (Lond). 2009 Jun 18. [Epub ahead of print]
July 1, 2009