An isolated heart preparation shows that when aortic pressure against which the ventricle ejects is acutely raised, stroke volume initially falls but then returns toward baseline over several beats without any change in end-diastolic volume. Which intrinsic mechanism explains this recovery?
- A Anrep effect, an increase in contractility in response to increased afterload ✓
- B Frank-Starling mechanism operating on increased preload
- C Bowditch staircase phenomenon secondary to increased heart rate
- D Baroreceptor-mediated sympathetic augmentation of contractility
Correct answer: A. Anrep effect, an increase in contractility in response to increased afterload
Explanation
The Anrep effect is a homeometric autoregulation in which a sustained rise in afterload produces a gradual increase in ventricular contractility over several beats, restoring stroke volume without any change in fiber length. It is thought to involve stretch-induced changes such as increased calcium sensitivity. The Frank-Starling mechanism requires altered end-diastolic volume, the Bowditch effect requires altered rate, and baroreceptors are absent in an isolated preparation.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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