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Health and medicine
Course: Health and medicine > Unit 3
Lesson 13: Cyanotic heart diseases- What is cyanotic heart disease
- Shunting in the heart
- Einsenmenger coarctation of aorta
- Tetralogy of fallot
- Truncus arteriosus
- Total anomalous pulmonary venous return
- Tricuspid atresia
- Transposition of great arteries
- Ebstein's anomaly
- Hypoplastic left heart syndrome and norwood glenn fontan
- Cyanotic heart diseases - Diagnosis and treatment
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Shunting in the heart
Created by Amy Fan.
Want to join the conversation?
- So... What happens when you don't have a left ventricle? Is there a cure, or do you just die as soon as you're born?(4 votes)
- What triggers circulatory transition when a baby is born?(1 vote)
- why is the resitance of lungs higher than the rest of the body in a newborn baby ? thanks in advance(1 vote)
- "Newborn" in this question isn't what we'd normally think of as a neonate (up to 28 days old), but much more about the first minutes to days after birth. There's a big change that happens in the lungs following birth: they inflate and expand for the first time, and blood vessels that have been mostly bypassed by the circulatory system start carrying large amounts of blood for the first time, and small vessels in the lungs which relax in response to alveolar oxygen start to open up.(1 vote)
- I have a question concerning the bronchial circulation. I have learnt that the bronchial veins can either drain into azygous vein or into pulmonary vein. the pulmonary vein carries oxygenated blood from lungs to the heart. the draining of bronchial veins into pulmonary veins means that the blood reaching heart is partly desaturated. does this have a minor effect that we can ignore? what does the body do to overcome such thing?(1 vote)
- The effect is minuscule, and it's not something we would normally think about in clinical practice. It's important to recognise that it exists and that there is a tiny drop in oxygen pressure from the alveolus to the left heart. This is the normal physiology and there's still plenty of oxygen, so the body doesn't have to do anything to compensate.(1 vote)
Video transcript
- I wanted to spend just
a tiny bit more time on the concept of shunting, just because it's so important
in what we're talking about. Shunting is used in a
lot of ways in medicine, and it just means pushing
something from where it's suppose to be or
used to be to a new place. Here we're talking about blood going from its natural place of flow
to a different place. And I wanted to introduce the
anatomically correct heart. I didn't want you to sit
here and watch me draw it, so I drew it in advance and here it is. So our heart doesn't actually
look like the cartoon. This is how it actually looks. And we'll just go through
this really quickly and label everything. So this is still the right side. And this is still the left side. The right side of the
heart receives blood, from the body that's used up. It's low in oxygen. So here we have the right atrium. And blood goes into the right ventricle. And here this blue thing that I've drawn connected to the right
ventricle, do you see how the blood in the right
ventricle goes this way, this is our pulmonary artery. Now every vessel that receives blood, going out of the heart is an artery. So even though this is
de-oxygenated blue blood, it's still an artery because
it's coming out of the heart. Then we have our left atrium
going to the left ventricle. And here this big red
structure, this is our aorta. Actually, let's just write
out the whole thing, aorta. So if I'm a drop of blood or
if I'm the Magic Schoolbus, this is how I would go
through this whole system. So coming in here or here, so the veins don't blood
into the right atrium. And I go through here
into the right ventricle. There's a valve here and
let's not worry about what it's actually called for the moment, just remember that it's there. So I'm in the right ventricle
and from here I get squeezed into the pulmonary artery. Again, this is the valve here. From the pulmonary artery,
I go to our wonderful lungs, and draw the lungs like this like a tree. It's the right and left
branches of the lungs. Here we pick up oxygen.
Now our blood has oxygen. The lungs return the blood
to the heart through, to the left atrium. Oh, I didn't draw those here. So here we have pulmonary veins. Even though it's carrying red blood now, since it's going back into
the heart, it's a vein. So pulmonary veins return
blood here and here, into the left atrium. So now I'm in the left
atrium and I'm going to the left ventricle through this valve. And this big left ventricle
pumps me into the aorta. And from the aorta, I
go all over the body, these little branches. And that's basically my path, through the heart and the lungs. So look at these little
discrete chambers and paths, the blood, even though it's
in all very close together, follows this pattern and
the de-oxygenated blood is separated from the side that has oxygen. So shunting, here again, we're
talking about right to left shunting because we are worried
about people turning blue, cyanotic, so this blue blood
on this side is going this way. And for shunting to happen, there are two things that need to happen. One, there needs to be a path. And two, there needs to
be somehow this force or pressure behind it to
make it want to go that way. This is just like plumbing. Not that I know anything about plumbing, but basically blood follows
the path of least resistance, just like water does. So let's think about
how we can create a path for that mix in the first place. So, one obvious one when we
look at these big chambers, we're gonna have a hole here. Also, people are born with
different holes in their heart. And sometimes they heal
up, sometimes they don't depending on what exact disease
or structural abnormality they have, so they're gonna
have a big hole there. The next place we're gonna have a hole is between the atrium. Oh, I didn't draw the septum here. So, there it is. And, of course, we're gonna
have a big hole there. Interestingly, everybody
is born with a hole here, but it usually closes within
the first few seconds, first few breaths you take. Or sometimes there's a hole
that's always gonna be there. And then for babies, especially
when they're in the uterus, there is a vessel here called
the "ductus arteriosus". Okay, let's write that up. Ductus. Arteriosus. And basically they need this
when they're in their mom's belly because we don't
breathe in the belly. And since we get blood from the placenta, this is a conduit to help
us get blood to the body. It has to do with fetal circulation. So the ductus actually
begins to slowly close as soon as we're born. So adults don't have this. In fact, even toddlers don't have this. But in the first few weeks of
life, this is a very real path for blood to still go back and forth. It's really cool that we
have medicine to keep it open or close it faster
depending on the situation. But just remember that it's there. Oops, I accidentally erased
part of my aorta here earlier. That's not supposed to be there. Okay, so now pressure. So I'm just gonna put over here
pressure equals resistance, resistance for r, times flow. That's just our little
physics for the day. All I want you to
remember from this is that pressure and resistance are related. So the left and right side
of the heart actually have huge differences in pressure
and that all depends on what they're pumping against. See the left ventricle is
pumping into the aorta, into the body, just pumping
against the resistance of our whole body's worth of vessels. So the left side, the
pressure actually equals our blood pressure. So jumping out of the
baby's mentality for awhile, for adults, what is our
perfect blood pressure? It's around 120, right. That's the systolic pressure
or the pressure the heart is pumping against when it's squeezing. So the left ventricle, when it squeezes, it's pushing against the 120
or so millimeters mercury. I'm throwing numbers out there just to, so we have the comparison. Because on the right side, the
ventricle is pushing, what, into the lungs. And the resistance in
the pulmonary vasculature is much, much lower than our whole body. So the right side is
actually pushing against-- The range is usually 9 to
18 millimeters of mercury. All this to show you that,
look at how much harder the left ventricle has to work
compared to the right ventricle. That's why in adults, in
functionally normal hearts, the left ventricle is a
lot bigger and stronger. It's just a stronger muscle
than the right ventricle. So if both of them squeeze
together and even if we have a hole here, you would
think that the normal shunt goes from left to right because
this side has so much more power and you'd be right
because we certainly have lot of diseases with left to right shunts. So when we have right to left shunts, which you think about why is
the right side overpowering. One important one is because
pulmonary vasculature in newborn babies have
high, high, high resistance. So initially the right side
is pushing against a lot more pressure than the left side. So that in a newborn babies, it's very easy to go right to left. Because given the choice,
the blood would rather go into left ventricle than
the pulmonary artery because the resistance in the lungs is so high. I'm gonna say that again just
because it's really important. So if you're a drop of blood,
go back to, let me use orange, if you have the choice
to go in here or in here, in a newborn, going into
the pulmonary artery is hard because the lungs are stuffed
and full of resistance. While going to the left is a lot easier, so it's gonna go this way. That's one important way
of right to left shunting. And that's why it's so
prevalent in newborns. In fact, in adults this can still happen. Adults can develop pulmonary hypertension. So the resistance can increase
because of some disease in adults and can still go right to left. So that's one way to go right to left, is the lungs giving us too much resistant. The other way is, look at this valve here. This is called the pulmonary
valve that connects the right ventricle to the pulmonary artery. This valve can be too tight. This artificially increases
the resistance here. So, again, blood given the
choice between here and here, is gonna want to go to the left side. So that's also how you get shunting. And sometimes in some cases, we don't even have a left
ventricle, it just didn't develop. In that case, the pulmonary
arteries and aorta can be plugged over here. They can be both receiving
blood from the right ventricle. I guess that's not really
shunting as much as blood from the right side and left side just
mixing together and going out. So this is not an exhaustive list of all the ways we can shunt, but the one thing I want to
use is to illustrate is that when you talk about the
specific defects in the heart, always be thinking about the
path the blood wants to go and the pressure, I guess, and resistance that's making it go that way. We got fluid and we got muscle and ducts. So no matter how it gets
structurally messed up, and then coming back to this picture, will help us understand why
this baby is blue or cyanotic.