Capacitance
<p>From: 'The Exercise Intolerance in POTS, ME/CFS and Fibromyalgia Explained?' <a href="https://www.healthrising.org/blog/2016/07/04/exercise-intolerance-fibromyalgia-chronic-fatigue-pots-explained/">https://www.healthrising.org/blog/2016/07/04/exercise-intolerance-fibromyalgia-chronic-fatigue-pots-explained/</a></p>
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"Low Blood Volume Not the Primary Problem"</p>
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Systrom found that these patients had low Qt and ventricular filling; i.e. their hearts were not filling enough with blood during diastole – the part of the heart cycle when the heart fills with blood. (We just saw a similar pattern in ME/CFS in “Chronic Fatigue Syndrome: A Small Heart Disease?” and “A Mestinon Miracle.”) A finding of reduced stroke volume augmentation indicated that the problem probably traced to low preload. Preload is defined by how much the heart muscle cells stretch as they expand to increase the volume of the ventricles during diastole.</p>
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Catheters enabled Oldham and Systrom to gather the data they needed for to correctly diagnose their patients.</p>
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(The end-diastolic ventricular pressure and volume measures both measure something similar; they all measure how large the heart gets as it contracts to fill with blood just before it pumps it out.)</p>
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A critical part of filling actually occurs outside the heart. As we begin to exercise our veins vasoconstrict or narrow and the muscle pump in our legs swings into action in order to push the blood upwards. After the blood takes a trip to the lungs to get rid of waste products and become oxygenated, it moves into both ventricles which expand like a balloon (diastole), and then in a rush pump the blood out (systole).</p>
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Systrom found, though, that hearts of the exercise intolerant patients are not expanding normally when they exercised. This inability to fill with more blood during exercise was why they exhibited low energy production (VO2 max).</p>
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Low Blood Volume Not the Primary Problem</p>
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When Systrom gave them IV saline to boost their blood volume most improved their Qt max. That suggested that low blood volumes did indeed contribute but here’s the kicker; even with the increased fluid intake, the exercise intolerant patients still had a reduced response to exercise.</p>
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That suggested that reduced blood volume was not the entire problem. Instead, as with Newton, Systrom’s evidence points to problems with what he called impaired “capacitance”, which refers to reduced constriction of the veins during exercise. As noted earlier, once exercise starts the veins should narrow in order to propel blood back up to the heart where it can be cleansed, oxygenated and sent off to the muscles again. That apparently was not happening normally in these patients.</p>
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What appeared at first to be a heart problem was actually a circulatory problem. We recently saw that Newton and Miwa found that blood flows to the heart in chronic fatigue syndrome (ME/CFS) are so reduced as to cause a substantial reduction in the size of ME/CFS patients hearts. This wasn’t because the hearts of ME/CFS patients were diseased (in heart failure the size of the heart actually expands) but because, like any muscle, the size of their heart muscle shrank when it wasn’t being worked enough.
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