What term describes the incremental increase in stroke work with increasing preload?

• A. Afterload
• B. Preload-recruitable stroke work
• C. Ejection fraction
• D. Cardiac output

Answer: (B)

The key idea is how preload influences the work the heart does with each beat. According to the Frank-Starling mechanism, when the ventricle fills more (higher preload), the muscle fibers are stretched more, leading to a stronger contraction and more stroke work. The term that captures how much stroke work increases for each unit of preload is preload-recruitable stroke work. It’s typically described as the slope of the relationship between stroke work and end-diastolic volume (or pressure), and it serves as a way to gauge contractile performance across different loading conditions.

Why this term fits best: it specifically quantifies the incremental increase in stroke work as preload rises, independent of other factors like afterload. In contrast, afterload is about the pressure the heart must work against; ejection fraction is a ratio of stroke volume to end-diastolic volume and doesn’t directly express how stroke work changes with preload; and cardiac output is the overall flow output (heart rate times stroke volume) rather than the preload–stroke-work relationship.