The amount of resistance in the circulatory system during venous return is known as:

• A. Venous Pressure (Pv)
• B. Right Atrial Pressure (Pra)
• C. Pressure Gradient
• D. Venous Vascular Resistance (Rv)

Answer: (D)

The concept being tested is what opposes the flow of blood coming back to the heart through the veins. Venous return is driven by a pressure gradient (the difference between mean systemic filling pressure and right atrial pressure), but the amount of opposition to that return is determined by the venous system’s resistance. This opposition is quantified as venous vascular resistance (Rv). In the relationship for venous return, flow back to the heart is proportional to the driving gradient (Pmsf minus Pra) and inversely proportional to Rv, so when venous resistance increases, venous return falls, and when it decreases, venous return rises. The other terms describe pressures or the driving force, not the resistance itself, which is why the correct term is venous vascular resistance.