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kev1987
04-01-2007, 10:44 AM
I (think I) understand preload and afterload but have a couple of questions.

I know aortic regurg causes increased afterload due to increased systolic BP, but i don't understand why. I always thought the BP would drop, as less blood is being pumped into the aorta (as more blood leaks back into the LV)

Also why does a mitral regurg cause a decrease in afterload? - surely with more blood leaking back into the atria, the ventricular pressure is lowered, making it harder for the ventricles to pump blood into thPA and aorta!

Any simple explanations would be great

MDiva
04-01-2007, 03:59 PM
"I know aortic regurg causes increased afterload due to increased systolic BP, but i don't understand why."

Since AV not closing properly at end of systole, you get no isovolumetric relaxation. You get an increased end systolic volume in LV because of the retrograde blood. Stroke volume goes up: SV = EDV-ESV. This increases systolic arterial pressure which is proportional to peripheral resistance. So per the equation for Mean Arterial Pressure or MAP = (SV x HR) x TPR, you get a rise in the pressure. Hope this helps.

MDiva
04-01-2007, 04:08 PM
"Also why does a mitral regurg cause a decrease in afterload? - surely with more blood leaking back into the atria, the ventricular pressure is lowered, making it harder for the ventricles to pump blood into thPA and aorta!"

You get an increase in atrial volume and pressure during systole. This is more of an effect on preload, I think?







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