Myocardial Oxygen Consumption — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysiology - CardiovascularMyocardial Oxygen ConsumptionFRCA Primary

Myocardial oxygen consumption per beat correlates more closely with left ventricular pressure-volume area than with external stroke work alone. During which phase is ventricular chemical energy converted predominantly into elastic potential energy while ventricular volume remains unchanged and no external stroke work is performed?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Isovolumetric contraction

Explanation lettering: C = shown as A · E = shown as B · A = shown as C · B = shown as E

D is correct. During isovolumetric contraction both the mitral and aortic valves are closed, so left ventricular volume remains at its end-diastolic value while pressure and wall stress rise rapidly. No blood is ejected and therefore no external stroke work is performed; the mechanical component of pressure-volume area is stored predominantly as end-systolic elastic potential energy. Pressure-volume area correlates closely with myocardial oxygen consumption, demonstrating why pressure generation can be energetically expensive despite absent shortening. Rapid ejection performs external stroke work as ventricular volume falls. Rapid filling and atrial systole occur at comparatively low ventricular pressure. Isovolumetric relaxation requires ATP-dependent calcium sequestration, but it dissipates systolic tension rather than generating the pressure-volume area described in the stem.

Reference: Han JC, Taberner AJ, Nielsen PMF, Loiselle DS. Relating components of pressure-volume area in Suga's formulation of cardiac energetics to components of the stress-time integral. Journal of Applied Physiology. 2012. https://pubmed.ncbi.nlm.nih.gov/22837173/