In a non-pathologic system, how does higher central venous pressure affect venous return and cardiac output?

• A. Higher CVP reduces venous return and CO.
• B. Higher CVP increases venous return and CO.
• C. Higher CVP has no effect.
• D. Higher CVP reduces venous return but increases CO.

Answer: (A)

The key idea is that venous return is driven by the pressure gradient between the mean systemic filling pressure and the central venous pressure (right atrial pressure). When central venous pressure rises, this gradient narrows, so less blood returns to the heart. In a normal, healthy heart at steady state, cardiac output equals venous return, so a drop in venous return leads to a drop in cardiac output. The reduction in venous return lowers preload, which reduces stroke volume via the Frank-Starling mechanism, and hence lowers CO. So, higher central venous pressure reduces both venous return and cardiac output.