Mean circulatory filling pressure (MCFP) in humans was defined by Guyton as "the pressure that would be measured at all points in the entiere circulatory system if the heart were stopped suddenly and the blood were redistributed instantaneously in such a manner that all pressures were equal".
Now according to many physiologists, there must be a location in the vascular network where the pressure is completely independent of the cardiac activity, and this pressure must be equal to the MCFP. Apparently, this was already noted by Starling in 1897. The entire point is well explained in this article.
I have read this article and some others introducing the concept of MCFP to medical students; many of them report the same observations made by Guyton, Starling, etc., but a point which is never addressed is why there must be a location in the vasculature where the pressure is independent of cardiac activity.
I feel like getting a satisfactory answer to this question would greatly improve my understanding of hemodynamics, so I would be very grateful if you could explain the concept to me.
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You've misread the linked article if you take this to mean there is some place that is unaffected by cardiac activity. It's just that there must be some place that is equal in pressure to the MCFP. The actual position fluctuates throughout the cardiac cycle.
The reason, though, that some place must be equal to MCFP is that pressure is continuous. Somewhere in the vasculature (i.e. proximal arteries) is definitely greater than the mean; somewhere else (i.e. proximal veins) is definitely less than the mean. Because the pressure varies continuously the function must pass through the mean at some point along the vascular path. This isn't anything special about biology, just mathematics.
answered Oct 25, 2020 at 20:20
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$\begingroup$ Thank you very much for your answer. I am well aware that, if MCFP is comprised between mean arterial pressure and right atrial pressure, then there must be a point in the vasculature at which pressure equals MCFP. But the article I mentioned seems to say that this point does not move with cardiac activity, as illustrated with the fact that the three curves in figure 3 intersect at a unique point. This is stated even more clearly in Rothe (1993), a work cited in the article. $\endgroup$ Commented Oct 25, 2020 at 21:28
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$\begingroup$ In Rothe (1993) the authors, citing Starling, state "Somewhere in the circulation there must be a point where the pressure is neither raised nor lowered and where, therefore, the pressure is independent of cardiact activity." $\endgroup$ Commented Oct 25, 2020 at 21:28
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$\begingroup$ @user47679 "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" - quoted from your source. $\endgroup$– Bryan Krause ♦Commented Oct 25, 2020 at 22:17
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$\begingroup$ They're talking about a hypothetical location that's constantly shifting. I think you're reading too much into it or taking it too literally. $\endgroup$– Bryan Krause ♦Commented Oct 25, 2020 at 22:17