Define preload reserve and describe how you would assess it using a PV loop protocol?

• A. Preload reserve is the ability to decrease SV with lower preload; assess by decreasing venous return and observing SV changes.
• B. Preload reserve is the ability to increase SV with higher preload; assess by progressively increasing venous return and observing SV changes on PV loop.
• C. Preload reserve is about afterload; assess by increasing arterial pressure.
• D. Preload reserve is about contractility; independent of preload.

Answer: (B)

Preload reserve is the heart’s ability to increase stroke volume when preload (venous return/end-diastolic volume) is increased. In a PV loop, preload is reflected by how much the ventricle fills before systole (the end-diastolic point). To assess it, progressively raise venous return and watch how the PV loop changes. If the ventricle has good preload reserve, increasing preload will shift the loop to a higher EDV and widen it, so stroke volume grows noticeably (the loop's width increases). If preload reserve is limited, stroke volume changes little despite higher preload. This approach directly links how much the heart can augment SV with changes in preload. The other statements describe decreasing preload, addressing afterload, or separating contractility from preload, which do not capture the concept of how SV responds to increases in preload.