Which statement best describes the Frank-Starling mechanism and its relevance in congestive heart failure?

Which statement best describes the Frank-Starling mechanism and its relevance in congestive heart failure?

• A. Stroke volume increases with preload, and in CHF the response is blunted due to reduced contractility.
• B. Stroke volume decreases as preload increases.
• C. Preload has no effect on stroke volume in healthy hearts.
• D. The Frank-Starling mechanism explains afterload regulation.

Answer: (A)

The main idea here is how the amount the heart fills (preload) influences how hard it can pump (stroke volume). In a healthy heart, increasing preload stretches the ventricular muscle fibers to a more optimal length, which boosts the force of contraction and raises stroke volume. In congestive heart failure, the heart’s ability to contract is impaired, so that extra filling doesn’t produce as large an increase in stroke volume—the response is blunted because contractility is reduced. This is why the statement that stroke volume rises with preload, but the rise is diminished in CHF due to lower contractility, best captures the Frank-Starling mechanism and its relevance in heart failure. The other ideas—preload not affecting stroke volume, or stroke volume decreasing with more preload, or the mechanism relating to afterload rather than preload—don’t fit the observed physiology.

The main idea here is how the amount the heart fills (preload) influences how hard it can pump (stroke volume). In a healthy heart, increasing preload stretches the ventricular muscle fibers to a more optimal length, which boosts the force of contraction and raises stroke volume. In congestive heart failure, the heart’s ability to contract is impaired, so that extra filling doesn’t produce as large an increase in stroke volume—the response is blunted because contractility is reduced. This is why the statement that stroke volume rises with preload, but the rise is diminished in CHF due to lower contractility, best captures the Frank-Starling mechanism and its relevance in heart failure. The other ideas—preload not affecting stroke volume, or stroke volume decreasing with more preload, or the mechanism relating to afterload rather than preload—don’t fit the observed physiology.