Any news on this front guys?
Still thinking about how these low SvO2 findings might be explained. An unpublished study by Dr. Karl Morten was presented (in 2018 I think). As far as I know this study has not been extended / replicated / published.
His group took healthy human muscle cells and measured oxygen levels in cells, first in healthy control plasma and then in ME/CFS patient plasma. There was a significant drop, as graphed.
This complemented Prof Ron Davis's cross-over study showing something in ME plasma affecting healthy cells. See this
blog post for details on these two studies and others.
If the "something-in-the-blood" leads to inefficient oxygen use by cells and drops intracellular oxygen levels, that might lead to oxygen hyperextraction from blood as a compensation. This might lead to the much lower venous oxygen levels observed.
That won't explain the proportion of ME patients that have abnormally high SvO2. Perhaps they have moved to a deeper level of metabolic adaptation that doesn't demand oxygen hyperextraction as a compensation.
Maybe the researchers plan to run this experiment with a range of ME patients' muscle cells. If anyone has seen any updates on this finding, please follow-on in this thread.