AEMCA Practice Exam

What is a major factor that can cause a decrease in stroke volume?

1. Increased preload

2. Decrease preload

3. Increase in heart rate

4. Better contractility

The correct answer is: Decrease preload

A decrease in preload is a significant factor that can lead to a reduction in stroke volume. Preload refers to the initial stretching of the cardiac muscle fibers prior to contraction, which is largely determined by the volume of blood returning to the heart. When preload is decreased, less blood fills the ventricles during diastole, leading to a reduced volume of blood being ejected with each heartbeat, known as stroke volume. Inadequate preload can occur due to various reasons, such as blood loss due to hemorrhage, dehydration, or conditions that impair venous return. As the amount of blood filling the heart decreases, the heart’s ability to pump effectively is compromised, which directly impacts the stroke volume and overall cardiac output. This understanding of preload’s role in stroke volume highlights the physiological principle that adequate filling of the heart is essential for optimal functioning. Therefore, when preload is reduced, the mechanical work the heart can perform in terms of ejecting blood diminishes significantly.