Pfo left to right shunt?
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Not a bad answer, Bush! You are close, but a bit inaccurate on some of the details!
First of all, it's a little unusual for pfos to shunt left to right. As you stated, the foramen ovale (the 'fo' in 'pfo') was there when we were babies so the blood could go right to left to bypass the lungs. But the pfo is not just a hole like a doorway in a wall. It's more like a flap like the way you have to open a pillow sham cover to get the pillow in? Normally the two sides of the flap seal shut, but in a pfo they don't. The way the flap is arranged, though, it can be pushed open from the right side but it's pushed closed from the left, so blood can't go left to right. Interesting...
There is something called an asd (atrial septal defect) that IS just a hole in the wall. ASDs let the blood go either way, and usually the blood wants to go left to right. So there is a possibility that the hole is actually an asd and someone is reading it wrong - trust me it happens a fair amount.
The reason blood flows left to right is not because the right side of the heart is much weaker, though. It's complicated, but blood mostly flows across the pfo/asd in diastole, so it's not really the pumping pressure that matters (as you suggest) but the filling pressure that matters. Since the right ventricle is thinner and floppier, it has a lower end-diastolic pressure which means a lower right atrial pressure. The left ventricle is thick and muscular which means a higher end-diastolic pressure which means a higher left atrial pressure. And, as you have said, blood goes from high pressure to low pressure.
Anyway, Amanda, you want to know whether you should be worried about the pfo, right? Well... it's a little complicated because it's supposedly a pfo but it shunts left to right. Usually a pfo is not a big deal. Did you know that a quarter of the entire world has a pfo! ASDs can be more of a problem, because if a LOT of blood goes left to right the lungs and the right sided chambers get a little overloaded and over years and years the chambers can start to get stretched out and the blood vessels in the lung can get injured and you can develop high blood pressure in the lungs. This is easy to follow though because if you have a left to right shunt a doctor will usually do an echocardiogram every couple of years to make sure there are no signs of high blood pressure in the lungs and no signs of the right side of the heart starting to fail. If there are any changes you can have the hole closed nowadays without surgery! Look up amplatzer and cardioseal on google to see the devices they use.
PFO is a patent foramen ovale. It means that the wall that separates the left atrium from the right atrium is not completely closed. All babies in the womb have this because blood doesn't need to go to the lungs (the baby's lungs at least). Immediately after birth, this hole closes which forces the blood to go to the lungs to get oxygen. This can take several days to occur, and in some people this hole never completely closes. The left to right shunt means that blood in the heart is flowing from the left side of the heart to the right side of the heart. The right side of the heart is much weaker because it on has to pump blood to the lungs, the left side is much stronger because it has to pump blood to the entire body. Fluids (in this case blood) always travel from higher to a lower pressure. The best way to have this checked out is an echocardiogram.
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