Define preload-recruitable stroke work.

• A. The incremental increase in stroke work obtainable with increasing preload, reflecting myocardial reserve.
• B. The maximum stroke work at a fixed preload.
• C. The stroke work that occurs independently of preload.
• D. The decrease in stroke work with increasing preload.

Answer: (A)

Preload-recruitable stroke work describes how much extra stroke work the heart can generate as filling (preload) increases, reflecting the heart’s contractile reserve. Stroke work is the energy the heart uses to eject blood each beat, and it rises when the pressure-volume loop expands with greater end-diastolic filling. As preload goes up, the cardiac muscle fibers stretch more, enhancing force of contraction through the length-tension relationship (the Frank-Starling mechanism). The key idea is the incremental increase: the amount of additional stroke work you can obtain by raising preload, which tells you how much reserve the myocardium has to boost performance when more blood returns to the heart. If contractility is limited, this incremental increase is blunted. This concept is distinct from stroke work measured at a single, fixed preload, and it is not a decrease with preload nor a stroke work independent of preload.