Blood Pressure (Cardiac output vs. constriction of arteries)

[destroythemcat]

I came across a question that asked:

Which has a larger effect on increasing Blood Pressure: Increasing cardiac output or constricting arteries?

Can anyone help answer the question?

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[mcloaf]

Unless what you wrote was a typo, it sounds like they're trying to see if you know that the control of peripheral resistance is largely from constriction of arterioles, not arteries.

 

[MedHopeful20134]

I would think that constricting arterioles would have a larger effect on BP, because constriction of arterioles would increase venous return, which would increase stroke volume and cardiac output.

 

[sillyjoe]

I would think that constricting arterioles would have a larger effect on BP, because constriction of arterioles would increase venous return, which would increase stroke volume and cardiac output.

Venus Return = Cardiac Output and they do not quantify the increase in cardiac output so how can you compare the two?

 

[MedHopeful20134]

Cardiac Output (CO) = Heart Rate X Stroke Volume.
Stroke volume should increase with increase in venous return (due to constriction of arterioles). This increase in cardiac output along with constriction of arteriole would, therefore, increase BP.

This is just my train of thought, please correct me if I am wrong.

 

[sillyjoe]

Cardiac Output (CO) = Heart Rate X Stroke Volume.
Stroke volume should increase with increase in venous return (due to constriction of arterioles). This increase in cardiac output along with constriction of arteriole would, therefore, increase BP.

This is just my train of thought, please correct me if I am wrong.

Venous return will always be equal to cardiac output in steady state conditions. Since they are not specifying how much they are increasing cardiac output (which would increase venous return an equal amount), how can you quantify that increasing artery resistance would increase cardiac output by an amount greater than just increasing cardiac output? They don't specify how much they increase it and your logic is using the fact that it would increase venous return more but cardiac output will always equal venous return in a steady state.

 

[MedHopeful20134]

Oh!
There is another concept of Starling's Law, which states that the heart will eject a greater volume of blood at higher pressures. So, if you fill the heart with more fluid (via increased venous return), it will stretch the heart muscle to an optimal length, and will result in a greater force of ejection. So by constricting the arterioles, systemic BP increases, which increases CO.

Just by increasing HR, blood pressure would not increase without arteriole constriction.

 

[mcloaf]

Cardiac Output (CO) = Heart Rate X Stroke Volume.
Stroke volume should increase with increase in venous return (due to constriction of arterioles). This increase in cardiac output along with constriction of arteriole would, therefore, increase BP.

This is just my train of thought, please correct me if I am wrong.

You're a little mixed up here. Arteriolar constriction decreases venous return, as it inhibits the movement of fluid to the venous side of circulation. It is a decrease in venous compliance via venous constriction that would increase venous return.