During isovolumetric relaxation, which of the following correctly describes the pressure-volume relationship within the left ventricle?
- A LV pressure rises, LV volume falls, aortic valve is open
- B LV pressure falls, LV volume remains constant, both aortic and mitral valves are closed ✓
- C LV pressure falls, LV volume increases due to mitral valve opening
- D LV pressure and volume both fall simultaneously as the mitral valve opens
Correct answer: B. LV pressure falls, LV volume remains constant, both aortic and mitral valves are closed
Explanation
Isovolumetric relaxation is the phase between aortic valve closure and mitral valve opening. The ventricle relaxes actively (energy-dependent Ca²⁺ re-uptake by SERCA2a), causing a rapid fall in LV pressure while LV volume stays constant since both valves remain closed. Mitral valve opens only when LV pressure falls below left atrial pressure (~5 mmHg), initiating rapid ventricular filling. The rate of pressure fall (−dP/dt) is a measure of ventricular relaxation (lusitropy).
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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