Capacitance in hemodynamics is defined as what?

• A. Volume Change / Time Change
• B. Volume Change / Pressure Change
• C. Time Change / Volume Change
• D. Flow Rate / Volume Change

Answer: (A)

Capacitance (also called compliance) in hemodynamics is defined by how much volume changes for a given change in pressure. In other words, it is the change in volume divided by the change in pressure (ΔV/ΔP). This reflects the venous system’s ability to store blood: veins have high compliance, so they can accommodate large increases in volume with only small rises in pressure, acting as a reservoir to smooth out fluctuations in venous return and cardiac output. The time element is not part of the definition—a time change would describe flow, not capacitance. So the correct concept is ΔV/ΔP, with units of mL per mmHg.