Physiology and Pathophysiology of the Venous System

A Guytonian explanation for hemodynamic responses to interventions in superficial venous disease

“…The ability of the vein wall to distend with increasing transmural pressure (net pressure exerted by the blood within the vein onto the vein wall) is its compliance, defined as the ratio of change in volume to change in transmural pressure (TMP). 5 This is a non-linear relationship with an S-shaped curve (represented schematically in Figure 2(a) and (b) by the unbroken blue line).…”

“…Venous resistance (R V ) is a measure of the energy required to maintain blood flow across that vein segment, and is the ratio of the energy gradient (ΔE) across the segment over the flow rate through that segment (Q) 5 i.e R V = ΔE/Q.…”

“…Venous resistance within a vein segment changes with the velocity of blood flow, blood viscosity, venous wall tone and changes in TMP. 5 The high compliance of the vein wall adjusts the R V to ensure adequate venous return. However, as TMP rises beyond physiological limits, venous wall compliance reduces, and R V rises rapidly with it.…”