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Venous Return Zero Point — FRCA Primary MCQ

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HardPhysiology - CardiovascularVenous Return Zero PointFRCA Primary

In a Guyton analysis, systemic venous return is plotted against right atrial pressure while stressed blood volume, vascular tone and resistance to venous return remain constant. The linear portion of the curve is extrapolated to its zero-flow intercept on the right atrial pressure axis, without inducing complete circulatory arrest. Which pressure does this intercept represent?

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Correct answer: D — Mean systemic filling pressure

The correct answer is D, mean systemic filling pressure. In Guyton’s model, systemic venous return is given by VR = (Pmsf − RAP)/RVR. At zero venous return, the pressure gradient is zero, so right atrial pressure equals Pmsf; Pmsf is therefore the x-intercept of the venous return curve. Mean circulatory filling pressure is the equilibrated pressure measured after cessation of all circulatory flow. It is often numerically close to Pmsf but is conceptually distinct, and complete circulatory arrest is excluded by the stem. Mean pulmonary filling pressure concerns the pulmonary circuit. Critical closing pressure describes vascular collapse or flow limitation rather than this extrapolated zero-flow intercept. Mean arterial pressure is not the upstream pressure governing systemic venous return.

Reference: Persichini R et al. Venous return and mean systemic filling pressure: physiology and clinical applications. Critical Care. 2022;26:150. https://pubmed.ncbi.nlm.nih.gov/35610620/