Which principle explains that increasing preload can increase the ejection fraction of the ventricle?

Which principle explains that increasing preload can increase the ejection fraction of the ventricle?

• A. Frank-Starling principle
• B. Laplace principle
• C. Poiseuille's law
• D. Bernoulli principle

Answer: (A)

The principle here is that the heart’s pumping strength rises when it is more filled. This is the Frank-Starling mechanism: increasing preload (the end-diastolic volume) stretches the cardiac muscle fibers toward their optimal length, which enhances the force of contraction. With a stronger contraction, more blood is ejected in systole, so stroke volume increases. Since ejection fraction is stroke volume divided by end-diastolic volume, a higher stroke volume from greater filling tends to raise the EF in a normal heart. The other listed principles describe different physical ideas (wall tension, flow through tubes, and dynamic pressure-velocity changes) and don’t explain how filling of the heart influences its contractile strength.

The principle here is that the heart’s pumping strength rises when it is more filled. This is the Frank-Starling mechanism: increasing preload (the end-diastolic volume) stretches the cardiac muscle fibers toward their optimal length, which enhances the force of contraction. With a stronger contraction, more blood is ejected in systole, so stroke volume increases. Since ejection fraction is stroke volume divided by end-diastolic volume, a higher stroke volume from greater filling tends to raise the EF in a normal heart. The other listed principles describe different physical ideas (wall tension, flow through tubes, and dynamic pressure-velocity changes) and don’t explain how filling of the heart influences its contractile strength.