“Your Blood is Black”: My ME/CFS Experience with HELP Apheresis in Germany

Naive perspective here, but the oxygen has to go somewhere, doesn't it? So if the theory is normal arterial oxygen and low venous oxygen, then you would pretty much have to find higher venous carbon dioxide and higher exhaled carbon dioxide than you would expect for a given effort, which I feel like we would have already seen in CPET results. I suppose you could have some level of build up of carbon dioxide in the blood (which would then lead to the dyspnea that some observe), but that seems like it would be fairly limited and only on a short time scale (and surely we would have seen that by now in blood pH).