@taniaaust1
I don't think readings as low as 7 are valid. Part of this has to do with the instrument measuring pressure, which becomes unreliable in a range for which it was not designed, and part of this has to do with your own state under these circumstances. When my pulse pressure gets much below 20, I am fighting to hang onto consciousness. The last time this happened my vision grayed out, and I had scarcely any idea what was going on around me.
Brains don't work very well when deprived of oxygenated blood.
Added: when I first posted this I wasn't sure of the density of mercury, and I looked this up. It is 13.55 times the density of water, and human blood is mostly water. Multiply 13.55*7 and you get 94 mm. and change. A pulse pressure of 7 is not even enough to raise blood 10 cm! (A few inches.) Your neck is probably longer, meaning such a reading says "Woops! no blood at all to the brain. Patient must be unconscious."
My body spent many years (maybe most of my life as it was that too not only early ME but also through my childhood) with pulse pressures of around 20, it was the normal for me. I guess due to this my body has probably adapted some to things others bodies may not handle.. just like if someone has high BP and is used to that, they may not handle having their BP in some normal ranges where others can.
Dr David Bell has said some ME patients can have such low blood volume that it would send a normal person into shock but that we adapt to it. I believe Im one of those (it takes 2 bags of 1L saline to help me when I have a collapse)
I havent been able to work out the actual point with the pulse pressure I go bad, of cause Im very bad when it has been at 7.. at that point Im on the floor or it has been a very transient reading with my BP shifting everywhere each time its taken so may of only been at that for a few seconds. My BP can be dramatically shifting moment to moment, its very unstable.
Its not supposed to be possible for a person to have the monitors coming up with BP readings of 0 dystolic either but the hospital found my BP was that low after I had to lay down before I collapsed after trying to stand test me.
The nurse actually freaked at my dystolic and yelled for a doctor who came running and they retested with a different monitor on the other arm and with the same one originally too again on the other arm. and once again that reading was gotten.. with the systolic being the same with the arms. (so they checked 3 times, 2 monitors actually they would of checked more cause of how I know how long it was at that for.. so it must of been checked at least 5 times on that occassion). I was at 0 dystolic with the two hospital monitors for 5? mins before my BP righted itself better.
The hospital actually did a letter about this reading on me. ( i think I have a copy of that letter in my thread here that i use here to journal and document things). I was able to still talk and answer questions at hospital montiors reading dystolic 0 (though I couldnt sit up at that or move around or I would of fainted)
I've had even weirder things happen. One time I think my blood may of ran backwards or something. The vein in my neck suddenly collapsed and started like sucking inwards as if my heart was sucking the blood back with the beats.
(I didnt have a monitor on that time..but that made me think that one of those holes some ME patients get must of opened in my heart or something (I have two leaky heart valves which can indicate one of those holes).. something really bad must of been going on for my neck artery/vein..the big one where you take neck pulse, to do what it did and go to noticably sucking in)