Seeing you are really helped with taurine, having low K+ AND Na+ (as you wrote on the
https://www.healthrising.org/blog/2...ndrome-pots-renin-aldosterone/#comment-988961 blog) makes sense to me. Just as having modest Mg and Ca while trying to up them.
Also the sentence "I can drink so much, but the water doesn't get into my cells" that Issie said so many times makes much more sense now. And now you say it too ;-).
Taurine is a main osmolite *inside* human cells. Being low on it makes the cells less osmolitic meaning they'll draw in less water. In other words: the water doesn't get into your cells.
Then the inner pressure in the cells decreases, and your cells become shrimpled. They'll risk even crushing in or imploding. Compare it to a WWO I submarine diving too deep. The water pressure will crush the submarine like if it were made from paper.
Something similar can happen if the inner osmolitic pressure in the cells is too low. Not a nice mental picture is it? Such "crumbled cells" risk quite a bit to be attacked by the immune system.
So the immune system has to be turned down as it sort of is the explicite task of the immune system to clean up "crumbled (own) body cells". Still, the many partly crumbled cells will have an increased chance at being attacked by the immune system. That's auto-immune problems.
At the same time: the immune system has to be turned down in order to not cause *massive* auto-immune problems. That's having the need for a weakened immune system.
And so we end up with another sort of paradox in ME and similar diseases: we seem to have both too strong AND too weak an immune system. See above ;-).
This "crumbling of cells" may be an essential part of POTS too. When standing up, the fluid / blood pressure on the lowest cells increases quite a bit. That means "crumbling those cells even more". It's a bit like getting that WWO I submarine in a lot deeper water. Its metal will start to make plenty of scary and loud sounds.
If so, the heart CAN'T increase it's pressure a lot to get the blood to the head quickly enough because that would further increase the pressure on those cells under siege in the lower legs. Adaptations must be done first. Slow increase of pressure to supply the head with blood sounds like POTS to me.
There do exist several potential options here, for example:
* Releasing (plenty of) histamine (in the *returning* or venous part of the blood flow). That increase the diameter of the veins returning to the heart. That reduces the pressure needed (on top of the pressure need to counter gravity) to push the blood back to the heart. Remember: having the same flow in wider tubes requires less pressure. So the local tissue doesn't have to press that hard to get the blood returning (to the heart) or it can reduce pressure.
* The histamine will also increase the permeability of local cells around the blood vessels. That means that water will easier get in and out of the blood vessels. When done around the returning blood vessels, it will increase the ease of collecting pooling blood / fluid for return to the heart. When done more at the capilaries in between the arterial and vein side, it will let leak plenty of fluid in the surrounding tissues. That does sound bad, but "organised fluid leak" is comparable to a safety valve in a heating installation or many other hydraulic installations. What happens if you have got a leak? Pressure drops! When done right, this again drops the dangerously high pressure (increase from standing up quickly) on the "crumbling" limb cells when quickly standing up.
One can say that the latter is increasing blood pooling in the legs. It is. It does however have the ability to (temporarily, until adaptions are complete) help reduce the mechanical (pressure induced) stress on the lower limb cells. There is no free lunch. Mast cells do have pressure sensitive receptors by the way. Those might help to decide to dump plenty of histamine.
This "dumping" of water in the intercellular space and connective tissue surrounding the capilaries will cause for some amounts of seconds less blood to return to the heart. A normal reaction of the heart then is to pump quicker but with smaller displacements (per pumping action / heart beat). That IMO helps protecting the wall of the heart chambers from damage (from dangerous underpressure and risk for rupture) when too few blood returns to the heart. I wrote on that one before. It will however cause very high heart rate while few blood reaches the head, feeling floaty headed or fainting.
When acummulating too long, it will increase pressure again a bit as "a full bag" exerts more pressure then "a less full bag". Compare it with the tension on the plastic of a kids baloon when filled to the brink with water or filled only with a bit of water. So the body can't allow this accumulation of fluids to exist for too long or it'll cause troubles too. Moving the legs by walking or fiddling a bit will help to remove both pooled fluids and pumping blood better back to the heart.
Too much of all of the above may weaken the tissues strength over (years of) time however... ...making preventing bad edema more and more challenging. In either case, having lower total blood volume, a common thing in our disease, helps to prevent too bad lower limb edema and reduces excess pressure when standing up quickly a bit too.
That may be another reason for the body to try and lower blood volumes. It may even be another partly reason for creating other osmolite imbalances (ratios between Na+ / K+ / Mg / Ca /...) in order to trigger a secondary drop in total blood volume...
The above is very very close to describing POTS plus POTS initiated MCAS in action.
I'm (very) far from an EDS specialist but I can imagine that having crumbled cells too isn't really helping "structural integrity". "Crumbling cells" do not necessarily need to mean a reduction of the size of the cells in all directions.
For example, when having a perfectly round and well inflated soccer ball and then releasing much of its air, it's total volume will decrease a lot. But it could turn more into a sort of a dish like shape when standing on it, up to the point that the (soccer) football has a *bigger* maximum diameter but a far lower height (then the fully inflated round ball).
When instead pulling at the only partly inflated soccer ball, it could become longer but less wide, resembling an American football that looks more like a bean.
Combine those visuals and you may end up with something like EDS when puling on limbs. It might be interesting to watch out for how EDS evolves with Meirav (and Issie) when they feel being able to hydrate better.