Which statement best describes time-varying elastance in LV pressure generation?

• A. LV stiffness remains constant throughout the cycle.
• B. LV stiffness changes during the cardiac cycle, with pressure approximated by E(t) × LV volume.
• C. The model ignores LV volume and uses fixed pressure.
• D. Elastance applies only to the systemic arteries.

Answer: (B)

The main idea here is that the left ventricle doesn’t have a fixed stiffness during a beat. In the time-varying elastance framework, the instantaneous pressure is governed by how stiff the ventricle is at that moment and how much blood is inside it. Mathematically, P(t) is proportional to the current LV volume scaled by the time-varying elastance: P(t) ≈ E(t) [V(t) − V0], where V0 is the unstressed volume. This means stiffness (E(t)) rises during systole as contraction strengthens, and falls during diastole as the ventricle relaxes, so pressure at any moment reflects both how full the ventricle is and how stiff it is at that time.

That’s why the best description is that stiffness changes during the cycle, with pressure approximated by E(t) × LV volume. The other statements aren’t consistent with this view: stiffness isn’t constant, the model uses volume (not fixed pressure), and elastance is a concept that applies to the ventricle (not exclusively to systemic arteries).