If venous return increases while contractility remains constant, what changes would you expect in the LV PV loop?

If venous return increases while contractility remains constant, what changes would you expect in the LV PV loop?

• A. End-diastolic volume increases; stroke volume increases.
• B. End-systolic volume increases; stroke volume decreases.
• C. End-diastolic volume decreases; stroke volume decreases.
• D. End-systolic pressure increases; stroke volume unchanged.

Answer: (A)

Increasing venous return raises preload, so the ventricle fills to a higher volume (EDV increases). With contractility unchanged, the Frank-Starling mechanism makes the heart pump more blood, so stroke volume increases. On the LV pressure–volume loop, this shows as a rightward shift (higher EDV) and a wider loop (greater SV). End-systolic volume would not be forced to rise; the key, observable change is that EDV increases and SV increases. This is why the best description is EDV increases and stroke volume increases.

Increasing venous return raises preload, so the ventricle fills to a higher volume (EDV increases). With contractility unchanged, the Frank-Starling mechanism makes the heart pump more blood, so stroke volume increases. On the LV pressure–volume loop, this shows as a rightward shift (higher EDV) and a wider loop (greater SV). End-systolic volume would not be forced to rise; the key, observable change is that EDV increases and SV increases. This is why the best description is EDV increases and stroke volume increases.