AEMCA Practice Exam

Which factor does not contribute to decreased stroke volume?

1. Increased contractility

2. Decreased preload

3. Increased afterload

4. Decreased heart rate

The correct answer is: Increased contractility

The factor that does not contribute to decreased stroke volume is increased contractility. In the context of cardiovascular physiology, stroke volume refers to the amount of blood ejected by the heart with each contraction. When contractility is increased, it means that the heart muscle is performing more effectively, allowing it to pump more blood into circulation during each contraction. This typically results in an increased stroke volume, as the heart is better able to overcome the pressures that oppose blood ejection. In contrast, decreased preload reduces the volume of blood filling the heart before contraction, which can lead to a lower stroke volume. Increased afterload signifies increased resistance the heart must work against to eject blood, which can reduce stroke volume as well due to the heart struggling to effectively pump against this increased pressure. A decreased heart rate can also contribute to a lowered stroke volume, as fewer heartbeats lead to a reduced total output over time, despite each individual contraction potentially being strong. Thus, increased contractility supports an increase in stroke volume rather than a decrease, highlighting why it is the correct choice in this context.