Ryan31337
Senior Member (Voting Rights)
They found some people had low end tidal Co2 levels when lying down, before doing the lean test. Yes, it's possible that the whole getting to the clinic and just being there is stressful, but why the variability between visits, with levels being low on some visits and not on others?
So, I'm hypothesising that the presence of PEM, or not, might account for the variability. And so it would be good to see a study that took into account whether the person with ME/CFS has PEM, or not.
As with a lot of this OI stuff it has been explored in greater deal, often with controlled studies, in the POTS literature over the past decade or so.
For example: the hypocapnia seen here is clearly not a stress response to the test. Healthy controls have been used in similar POTS studies and do not show the significant drop in ETCO2 that we see in patients when put through the same stand/tilt table tests. The hypocapnic POTS patients also exhibit hyperpnea, not tachypnea, so don't fit an anxiety hyperventilation response - primary anxiety/HV patients have also been recruited to confirm this.
A leading theory is that the hyperventilation in POTS is caused by "a mechanism involving peripheral chemoreflex sensitization by intermittent ischemic hypoxia".
We know in these POTS patients CBF is reduced with orthostasis, hyperpnea and hypocapnia then follow - this has been observed and replicated in multiple controlled studies. The theory states that a reduction in CBF implies a reduction in carotid artery and carotid body blood flows. This is referred to as a stagnant or ischemic hypoxia, which the carotid body cannot distinguish from hypoxic hypoxia. So these patients are thought to have a type of chronic intermittent hypoxia, which increases the peripheral chemoreflex sensitivity to hypoxia. Lots of complicated words to suggest repeated orthostasis alters the patients breathing response.
Although ME/CFS patients don't necessarily exhibit the tachycardia issues defined by POTS, they can show reduced CBF, so presumably this theory and its chain of events could also apply here.