How would you characterize preload reserve in a lab PV loop protocol?

• A. A steep SV vs EDV slope indicates high preload reserve.
• B. Preload reserve is not measurable in PV loop protocols.
• C. Preload reserve refers to the plateau of EDV with SV constant.
• D. Preload reserve is defined as the maximum EDV achieved without SV change.

Answer: (A)

Preload reserve is the heart’s ability to increase stroke volume as filling (preload) increases. In a lab PV loop protocol, you vary preload and watch how SV changes with EDV. A steep SV versus EDV slope means that small increases in filling produce large increases in stroke volume, signaling high preload reserve because the ventricle efficiently translates extra filling into more output. If the relationship is flat, the ventricle has low preload reserve since additional filling doesn’t boost SV much. Describing preload reserve as a plateau or as the maximum EDV reached without any SV change doesn’t capture the core idea, which is how responsive SV is to increasing preload.