**Figure 3.
Idealized "venous return curve".** Basis of
interpretation of venous return (Qr) as driven by (Pmc – Pcv).
The linear sloped segment can be described mathematically as Qr =
K(Pmc – Pcv) where K is the the slope of the segment and Pmc is
the value of Pcv at zero flow. This would describe a hydraulic
system in which venous return was driven through a resistance by
the pressure difference between a fixed source at Pmc and the
varied pressure, Pcv, at the outflow. The value of the resistance
is obtained as the negative of the reciprocal of the (negative)
slope, i.e. (-1)/K. However, this resistance does not correspond
to the physical resistance in the model in Figure 1. In
electrical terms, it is a composite whose value depends upon the
values of all the resistances and capacitances in the circuit