Reduced oxygen extraction is also seen in sepsis, where the microcirculation is disturbed.
Is the microcirculation involved in ME/CFS etiology?
I have gathered some knowledge about the microcirculation and sepsis (Ref 2):
The key physiological function of the microcirculation is to provide oxygen transport to the tissues to sustain cellular and thereby organ function. The microcirculation is composed of a network of arterioles, capillaries, and venules that connect the arterial and venous systems. The morphology of this network has highly heterogeneous structure that differs from organ to organ depending on the regional metabolic demand and function. Besides the important function of the regulation and distribution of oxygen within the different organ systems, the microcirculation plays a key role in the immun system and delivers a variety of nutrients and homones to the parenchymal cells. In addition the microcirculation has a variety of other specialized functions in certain organs, such as thermoregulation.
Under resting conditions oxygen uptake represents only around 25% of delivered oxygen, leaving a large reserve of oxygen to be extracted under conditions of decreased oxygen delivery. This is done by increasing the oxygen extraction ratio.
A study showed that oxygen uptake varies as a function of delivered oxygen in patients with sepsis, suggesting a lack of the ability to increase the oxygen extraction ratio.
Two theries have been developed to explain this:
- oxygen transport to the tissue gets shunted from the arterioles to the venules, which leaves the microcirculation hypoxemic
- sepsis-induced mitochondrial inability to utilize oxygen
There are several techniques available to follow the passage of oxygen from the microcirculation to the mitochondria.
It could be interesting to use these techniques in ME/CFS research. Perhaps ME/CFS patients also have some sort of microcirculatory and mitochondrial distress syndrome?