Question on UW ID#943 typo???

[godchaser1016]

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It says "At a given left ventricle preload, an increase in LV contractility tend to increase increase LV. afterload" in one of the answer choices.

How does contractility increase afterload?? It seems counterintuitive and perhaps I am missing something. Any comments guys??

 

[Step1Hash]

I havn't review cardio yet but all I can think of is that an increase in contractility will increase stroke volume and on the next beat the blood in the aorta is now more than it was before so the afterload is greater. Over time as the blood circulates you will have a greater preload to match that afterload and be back in equilibrium with the higher contractility.

Someone correct me if i'm wrong...i'm sure there's some equation somewhere that can explain this as well.

 

[bobsagat]

I havn't review cardio yet but all I can think of is that an increase in contractility will increase stroke volume and on the next beat the blood in the aorta is now more than it was before so the afterload is greater. Over time as the blood circulates you will have a greater preload to match that afterload and be back in equilibrium with the higher contractility.

Someone correct me if i'm wrong...i'm sure there's some equation somewhere that can explain this as well.

I'm not so sure about that... The question being referenced is one where a patient has mitral regurgitation, so we have to keep that in mind. Wouldn't the mitral regurg also build up effective "afterload" in the backwards direction as well?

Regardless, I think it's easier to see why this isn't the correct choice to answer the question, since even if we can't agree that regurg is made worse by increasing contractility, it's hard to see how it would make it any better. The ratio of regurgitated and forward-flowing blood should stay the same, right? In fact , I could see an increased systolic pressure forcing the valve open further.

 

[godchaser1016]

I'm not so sure about that... The question being referenced is one where a patient has mitral regurgitation, so we have to keep that in mind. Wouldn't the mitral regurg also build up effective "afterload" in the backwards direction as well?

Regardless, I think it's easier to see why this isn't the correct choice to answer the question, since even if we can't agree that regurg is made worse by increasing contractility, it's hard to see how it would make it any better. The ratio of regurgitated and forward-flowing blood should stay the same, right? In fact , I could see an increased systolic pressure forcing the valve open further.

Yea I understand why that answer choice is not the correct answer. I just had a problem with the statement made by UW. Thank you!