Basic pressure: an important feature of the vascular system

Starling's concept, "mean systemic pressure", is considered and its implications discussed. It is argued that since cardiovascular capacity and blood volume must obviously always be identical, any addition to or loss from the blood must simply compel an identical change in vascular capacity, without necessarily being associated with any change in venous return. Reasons are given for a need to differentiate between pressure and compression, and for appreciating that though the two are usually equal to one another, the second is not the cause of the first (as it is often thought to be). Indeed, the origin of blood pressure is the net osmotic pressure of plasma. We have demonstrated experimentally that Starling's method of measuring "mean systemic pressure" did not correspond to mean vascular compression during life. Moreover, when we remeasured mean systemic pressure by a method not much different from Starling's own, we arrived at quite a different figure. This fact we have attempted to explain. Finally we have described an entity which we hold to be more closely representative of mean systemic compression during life, and have shown how to arrive at it.