This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Which of the following would cause a decrease in stroke volume, when compared with the normal resting value? 
Select and explain. 
A. Reduction in afterload, B. An increase in end-diastolic pressure, C. Stimulation of the vagus nerves, D. Electrical pacing to a hea rateof 200 beats/min
D: Electrical pacing to a hea rateof 200 beats/min
Answer: D: Electrical pacing to a hea rateof 200 beats/min 
Explanation: Electrical pacing to a hea rate of 200 beats/min would decrease the time for filling and reduce end-diastolic volume.A reduction in afterload would make it easier for the ventricle to eject blood and would raise stroke volume.An increase in end-diastolic pressure will increase end-diastolic fiber length and increase the force of contraction and stroke volume.Stimulation of the vagus nerves slows the hea, increases the time for ventricular filling, and increases stroke volume.Stimulation of sympathetic nerves to the hea increases hea rate and contractility.Despite the decreased filling accompanying an increase in hea rate, stroke volume will stay the same or increase because of the increased contractility