A decrease in parasympathetic stimulation of the SA node would act to increase cardiac output.
When the parasympathetic nervous system is less active, it allows the heart rate to increase. The SA node, or sinoatrial node, is responsible for initiating the heartbeat by generating electrical impulses that set the pace for the heart. Increased stimulation of the SA node leads to a higher heart rate, which in turn increases cardiac output, defined as the volume of blood the heart pumps per minute.
Let’s briefly analyze the other options:
- An increase in afterload typically works against cardiac output because it makes it harder for the heart to eject blood.
- A decrease in end-diastolic volume (EDV), which refers to the volume of blood in the ventricles at the end of filling, would also lower cardiac output as there is less blood to pump out during contractions.
- An increase in parasympathetic stimulation of conduction fibers would likely decrease heart rate and thus decrease cardiac output.
In conclusion, the correct answer is a decrease in parasympathetic stimulation of the SA node, which effectively increases the heart rate and cardiac output.