I'm really struggling to understand venous return curves and their relationship to mean systemic filling pressure.
I understand mean systemic pressure is the pressure that would be measured throughout the cardiovascular system if the heart stopped beating and hence pressure would be the same throughout the body and no blood flow because there is no pressure difference.
I'm very confused about the effect of gravity on this, surely if you are standing up the pressure of the blood pooled in your extremities is greater, so is this value just a mean of all the pressures? And I don't understand the usefulness of this parameter, this occurs when the heart has stopped functioning so why do we relate MSP to be a part of the pressure differential driving venous return in the equation:
Vr = (MSFP - PRA)/venous resistance
One might notice that during this entire process, somewhere in the circulatory system there is a points which remains at a stable pressure (which happens to be the MCFP), irrespective of the catastrophic events reverberating through the rest of the organism. Rothe (1993) thought that this probably happens in small venules (less than 1mm diameter), and that it is not constant - present at different points of different organs, and changing constantly depending on prevailing conditions.
I think this means that MSFP might be the high starting pressure in the venules that drives flow towards the right atria and so the MSFP being equilibrated pressure if a heart fails is just that. But I find that arbitrary and entirely confusing.