How would a decrease in blood volume affect both stroke volume and cardiac output?

• A. It would increase stroke volume but decrease cardiac output.
• B. It would increase stroke volume and cardiac output.
• C. It would have no effect on stroke volume and cardiac output.
• D. It would decrease stroke volume and cardiac output.

Answer: (D)

Verified step by step guidance

1. Understand the relationship between blood volume, stroke volume, and cardiac output. Stroke volume is the amount of blood ejected by the heart in one contraction, and cardiac output is the total volume of blood pumped by the heart per minute, calculated as stroke volume multiplied by heart rate.
2. Recognize that a decrease in blood volume means there is less blood available to fill the heart during diastole (the relaxation phase), which leads to a reduced end-diastolic volume.
3. Apply the Frank-Starling law of the heart, which states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart. Conversely, a decrease in blood volume will lead to a decrease in stroke volume.
4. Since cardiac output is the product of stroke volume and heart rate, a decrease in stroke volume due to reduced blood volume will also lead to a decrease in cardiac output, assuming heart rate remains constant.
5. Conclude that a decrease in blood volume will result in a decrease in both stroke volume and cardiac output, as there is less blood to pump with each heartbeat and overall per minute.