Increase or decrease in preload with pregnancy?

[purplebanana]

Hi guys,

I have a question about preload and pregnancy.
In FA, it states "Vasodilators (eg. nitroglycerin) decreases preload." which makes sense to me and also google confirmed what I thought. That when you have decreased SVR blood there is less venous return thus decrease preload. Vasodilators are released in pregnancy.
However... I just did a practice problem from uworld and in the explanation they say..

If the preload is increasing due to the increased blood volume I can understand that but this explanation says that decreased SVR also contributes to the inc. preload.
Can someone offer some type of clarification on the contrasting answers??
Thank you so much!

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[AlteredScale]

Hi guys,

I have a question about preload and pregnancy.
In FA, it states "Vasodilators (eg. nitroglycerin) decreases preload." which makes sense to me and also google confirmed what I thought. That when you have decreased SVR blood there is less venous return thus decrease preload. Vasodilators are released in pregnancy.
However... I just did a practice problem from uworld and in the explanation they say..View attachment 347082
If the preload is increasing due to the increased blood volume I can understand that but this explanation says that decreased SVR also contributes to the inc. preload.
Can someone offer some type of clarification on the contrasting answers??
Thank you so much!

I think its the mixture of the two. If you only decrease SVR then you get pooling and a shift in CO if your pressure gradients remain the same. But because you have a much larger pressure gradient in pregnancy + vasodilation then you get a much higher VR and thus higher preload. It's based on this equation: VR = deltaPressure (RA-systemic venous system)/SVR