Question about a cardiovascular change in preganancy.....

[Knicks]

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Kaplan says that Plasma Volume increases with pregnancy.

Kaplan also says that Systemic Vascular Resistance = Blood pressure divided by cardiac output, and that since BP decreases and CO increases, the Systemic Vascular Resistance decreases.

My confusion:

If plasma volume increases during pregnancy, why/how is blood pressure decreased?

 

[butaloh666]

Kaplan says that Plasma Volume increases with pregnancy.

Kaplan also says that Systemic Vascular Resistance = Blood pressure divided by cardiac output, and that since BP decreases and CO increases, the Systemic Vascular Resistance decreases.

My confusion:

If plasma volume increases during pregnancy, why/how is blood pressure decreased?

You've answered your own question in the post above. BP normally decreases during pregnancy because of the decrease in SVR. This reduction in SVR is secondary to the vasodilatory effect of progesterone on the arterioles, and produces a lowered BP despite the rise in plasma volume.

 

[Knicks]

^^ hmm, thanks.

Yeah, it was the rise in plasma volume that confused me.

So I guess that means that the decrease in SVR is greater than the increase in plasma volume, since the BP is ultimately lowered, right?

 

[butaloh666]

^^ hmm, thanks.

Yeah, it was the rise in plasma volume that confused me.

So I guess that means that the decrease in SVR is greater than the increase in plasma volume, since the BP is ultimately lowered, right?

Well they're not directly comparable, but yes the effect of the lower SVR overshadows the rise in plasma volume.

 

[45408]

Hormones. The answer to any question about pregnancy is hormones. 😀


but yes, the progesterone's effect on BP overshadows the plasma volume increase.

 

[Knicks]

lol

Thanks, guys.

 

[TMP-SMX]

Smooth muscle relaxation secondary to progesterone. Women have a lot of edema because the increased fluid volume goes somewhere (obviously the fetus is one such place).

 

[45408]

Smooth muscle relaxation secondary to progesterone. Women have a lot of edema because the increased fluid volume goes somewhere (obviously the fetus is one such place).

In a normal patient (i.e., not one with pre-eclampsia), is the worsening edema in later pregnancy due to the worsening venous return as the uterus grows?

 

[TMP-SMX]

That is also one of many reasons for normal edema of pregnancy. IVC compression. Positioning the patient in LLD relieves the compression.

I believe the non-dependent edema of pre-eclampsia is similar to a nephrotic picture by losing colloid protein into the urine though apparently studies have shown that the cause is endothelial injury. (Makes sense due to the very common similarities of lupus and pre-eclampsia). Many of the prevailing theories on pre-eclampsia and the resulting risk factors link it to an immune response to the fetus. (Living with the spouse prior to having a child reduces the risk of pre-eclamspia).