How does preload affect stroke volume?

How does preload affect stroke volume?

• A. Increased preload reduces stroke volume.
• B. Increased preload leads to greater stretch of the heart muscle, enhancing contraction strength.
• C. Preload has no effect on stroke volume.
• D. Preload only affects heart rate.

Answer: (B)

Preload is the amount of blood returning to and stretching the ventricles at the end of filling. When preload increases, the ventricular muscle fibers are stretched more, bringing sarcomeres to a length that allows for more effective cross-bridge formation between actin and myosin. This length-dependent activation strengthens the contraction, so more blood is ejected with each beat. In other words, stroke volume rises as preload rises, up to a physiological limit. This is the Frank-Starling mechanism, which helps match the heart’s output to the volume it receives. So, increasing preload leads to greater stretch and a stronger contraction, increasing stroke volume. The idea that preload reduces stroke volume, or that it has no effect, or that it only affects heart rate, doesn’t align with this fundamental relationship between filling, muscle stretch, and contractile force.

Preload is the amount of blood returning to and stretching the ventricles at the end of filling. When preload increases, the ventricular muscle fibers are stretched more, bringing sarcomeres to a length that allows for more effective cross-bridge formation between actin and myosin. This length-dependent activation strengthens the contraction, so more blood is ejected with each beat. In other words, stroke volume rises as preload rises, up to a physiological limit. This is the Frank-Starling mechanism, which helps match the heart’s output to the volume it receives.

So, increasing preload leads to greater stretch and a stronger contraction, increasing stroke volume. The idea that preload reduces stroke volume, or that it has no effect, or that it only affects heart rate, doesn’t align with this fundamental relationship between filling, muscle stretch, and contractile force.