Understanding the Mechanics of Breathing

Hi Ninja Nerds, in this video we're going to talk about the mechanics of breathing. So it's going to be a tough topic for certain people to understand, especially with the pressures. So we're going to do our best here at Ninja Nerd Science to make sense of that. So let's go ahead and dig right in. So before we do that, we need to look at a little bit of anatomy for the lungs and a lot of the chest wall structure. So let's do that first. So if you look here, we have two lungs, right? Right, left lung. And what's going to happen is you're going to have, you know, the actual trachea. The trachea is going to branch off into the right and left primary bronchus, serving the actual... Lung, specifically at the smallest structural unit called the alveoli. We'll talk about that in a second. But the lung itself, each individual alveoli is making up the lung. But if you look at the lung, it has this nice little thin epithelial tissue with a little bit of areolar connective tissue clinging on to that organ. So you see this blue layer right there? That blue layer right there, we're going to denote this layer right here. Let's call this layer one. Okay, so layer one right there. So layer one is specifically called the actual visceral pleura. So again, this layer one is actually called the visceral pleura. Okay, that's the first layer. Then let's keep working our way out. Now you see this space right here, this little hollow like cavity, but it has a little bit of fluid in it. This space right here, we're going to call this. Number two here. So number two. Number two is actually this whole cavity here is actually specifically called the pleural cavity. Now here's what's interesting about the pleural cavity. In this diagram, I'm actually showing a space. In the human body, there actually is no space. It's actually a potential space, they call it. And the reason why is in our human body, the lungs, this visceral pleura is tethered or connected. to the actual, this pleura right here, this last one we'll talk about. This last one here is called the parietal pleura. Let me write this one down. Again, this third one is specifically called the parietal pleura. But to come back to that thought that I was saying, remember, this visceral pleura is almost completely tethered to the parietal pleura. And how they're tethered together and connected together is through this actual pleural cavity. What's... in the pleural cavity. Pleural fluid. There's a little bit of like a serious like fluid in here that allows for, imagine this for a second. Let's say here I take the eraser. The eraser is supposed to represent the visceral pleura. Here's the marker. This is supposed to represent the parietal pleura. Technically they are really really close together rubbing up against one another all the time. Now you might be saying, oh wait but if that happens all the time wouldn't that produce friction and inflammation and tissue damage? It would. But guess what our body does to prevent that from happening? That pleural cavity is occupied by what's called a pleural fluid that we said. And what that pleural fluid does is when the actual layers are rubbing up against one another during the inhalation and expiration processes, it allows for there to be no friction or very little friction and prevents inflammation. What happens when actually in certain situations where there is too much fluid accumulation or actually there's very little fluid accumulation, and these layers start rubbing up against one another and start causing a lot of agitation, it can produce what's called pleurisy. So that is a condition that can come about whenever there is a lot of friction developing between the parietal pleura and the visceral pleura due to maybe a decreased situation and not enough pleural fluid being produced. Okay, so again what do we have here? We have the pleural cavity, number two, and number one we have the visceral pleura. Okay, now we need to talk about something else. We need to talk about pressures because pressures is an important topic that we need to talk about here. Okay, there's three main pressures that we're going to talk about. Let's denote these A, B, and C. Okay, so we're going to call these pressures A, B, and C. So this is going to be pressure A, this is going to be pressure B, and this is going to be pressure C. Okay? Pressure A, pressure B, pressure C. Pressure A, we're going to just name them first. Pressure A is actually referred to as the intrapulmonary pressure. So it's referred to as the intrapulmonary or intraalveolar. Sometimes they call it intraalveolar pressure. Okay, and why did I say intraalveolar? Well, you really know what happens is, you know, technically whenever the trachea is coming here, it's going away to the bronchi, and then it goes secondary, tertiary, and then eventually goes to terminal bronchials, respiratory, and it branches out to these actual small structures. You see these little sacs here? These small little like... Grape-like structures, those are called the alveoli. So technically, when I say intrapulmonary pressure, I really mean intraalveolar pressure, right? Which is the pressure in here. So this is the A pressure, right? The pressure that we were talking about. But I'm just blowing it up here for the sake of this video so it's very clear, right? So, intrapulmonary pressure is this one. What is this B pressure? What is the pressure here in this pleural cavity? It's called the intrapleural pressure. Not that bad, right? Not that bad to remember. So again, what is this pressure here? It's called the intra-plural pressure. Okay, sweet deal. And again, it's the pressure that actually will be occupied in this pleural cavity. The last one, which is the C pressure, is the atmospheric pressure or the barometric pressure. You might have even heard of that as barometric pressure or atmospheric. They're called barometric pressure or atmospheric pressure. Now why am I saying all this stuff? Because this is going to be critical. Once we get these actual pressures down, the numbers down, it's going to make this whole mechanics a lot easier. Okay, so now what we're going to do is we're going to give you numbers for each one of these pressures. I'm going to explain a little relationship between the two. Okay, so I'm going to write these down here. So the intrapulmonary pressure is approximately, approximately, and we're going to denote it as P pull, okay? And P pull is just denoting that it's the intrapulmonary pressure. It is approximately 70 degrees. 760 millimeters of mercury. That's the unit that they're actually measuring it in, right? Then this next one, intrapleural pressure. Intrapleural pressure is approximately, and we're going to denote this as PIP. So we're going to denote this as PIP, representing that it's intrapleural pressure. Intrapleural pressure is approximately, it's always negative. We refer to it as a negative pressure. And I'll explain what that means when I mean negative pressure. Just hang in there a little bit. Intrapolar pressure is always less than the intrapulmonary pressure. You might be like, okay, well how much? About four millimeters of mercury less than the intrapulmonary intraalveolar pressure. So what's four minus 760 is about 756. So this is approximately 756 millimeters of mercury, which again is the units for this pressure. And the last one is going to be the atmospheric pressure. And the atmospheric pressure or the barometric pressure at sea level, at one atmosphere usually, we say is approximately about 760 millimeters of mercury. Okay. So let's write this one down. We'll put P and we'll put atm, which is atmospheric pressure. This is approximately 760 millimeters of mercury. And again, millimeters of mercury is the unit. Sometimes they use centimeter of water in certain situations, right? Okay. We're going to use millimeters of mercury in this situation. We're not going to use centimeters of water. Okay, now that we have all the pressures, I want to explain a little bit about these pressures. Primarily, one of the ones that bug people out a lot is the intrapleural pressure. I want to talk about this a little bit. Before I do that, though, I want to correlate this thing I'm going to talk about. I'm going to use these terms a lot, negative and positive and zero pressures. When we compare pressures, so if it's zero pressure, negative pressure, positive pressure, we compare it to the atmosphere. Okay, so for example, the atmospheric pressure is... 760 millimeters of mercury, all right? What is the intrapulmonary pressure? 760 millimeters of mercury. What is 760 minus 760? It's zero. So this is called, this is actually technically, we can also write that this pressure here, this intrapulmonary pressure is also zero millimeters of mercury, right? And that's because, so sometimes, just so you know, these can be interchangeable. I could put 760 or I could put zero. All that means is that it's equal to the atmospheric pressure, okay? Okay, now let's compare intrapleural pressure to atmospheric pressure. Okay, 760 minus 756 is 4 millimeters of mercury. But, when we think about this one, okay, what we're actually doing is, I should actually rephrase this. When you're subtracting, you're subtracting intra-pulmonary minus atmospheric. And you're subtracting intra-pleural from atmospheric. So, if I'm actually subtracting 760 from 760, it's 0. But, if I subtract 756 minus 760, what is that? that that's negative four okay sorry about that max up right all right so now this intrapulmonary pressure technically we could also write that it is actually negative four millimeters of mercury Okay, now that we have these numbers out of the way right so this is a negative pressure This is a zero pressure here. I want to explain why this is negative because this this bugs people out Okay, so let me take intrapleural pressure down here. I want there's three reasons why intrapleural pressure is actually negative So let me explain this real quick so intra Pleural Pressure Or as we denote it here, we denote it as the PIP. I'll refer to this a lot, right? So it's a negative pressure. There's three reasons why this is a negative pressure. Okay, first reason is the elasticity of the lungs. Okay, so the first reason is the natural elasticity of the lungs. Second reason is what's called surface tension. We'll have another video specifically on surface tension and surfactant. But this one is going to be surface tension. And then the last thing is going to be the elasticity of the chest wall. So the last thing is going to be the elasticity of the chest wall. Okay, let me explain what I mean by this. And there's also one last thing that I'll mention, and it's not with respect to this, it's due to the differences in the intrapleural pressure throughout the intrapleural cavity, and this is due to gravity. I'll mention this last one, okay? But again, this is not really one of the things that's contributing to it. It's contributing to a difference in the pressures. So it can contribute to the differences in the pressure. I'll explain what I mean by that because you can see that the pressure, interpolar pressure, can be different here, here, and here. And I'll explain that. First off, elasticity of the lungs and the surface tension. We're going to group those together for a second and let me explain why. Now, first off, what is the definition of elastance? How would you define elasticity? Elasticity is whenever you try to stretch something, right? It doesn't want to be stretched. It wants to resist the actual desire to be stretched. It wants to recoil. It always wants to assume the smallest size possible. That's what elasticity is. Think about this for a second. Where is this elasticity coming into play? Well, technically, Whenever the lungs want to re-quilt, what are they actually doing? Imagine, again, I told you that imagine the parietal pleura and the visceral pleura as actually close together, as actually touching. When I try for my lungs to actually deflate, if I try to deflate them, what is it going to do to the visceral pleura? It's going to pull it away. As it pulls it away, because it's trying to deflate, it's trying to get smaller. As the lungs is trying to get smaller, it's pulling away from, pulling this visceral pleura away from the parietal pleura. Now, Let's do surface tension. What is surface tension doing? Surface tension is this concept that because of the water molecules, this interaction between the air and the alveoli and the water molecules, it causes this tension at the air-water interface. And the whole thing is that the alveoli wants to collapse. It wants to assume the smallest size possible. So in other words, same thing. What's the overall purpose? The lungs are trying to pull this visceral pleura away from the parietal pleura. Okay. Well, that's trying to collapse the lungs and increase this volume. volume here. Okay, that's one thing that's happening. The next thing that's happening is the elasticity of the chest wall. Okay, what's the chest wall trying to do? Well, you know normally our chest wall is decently elastic. There's a lot of, you know, the coastal cartilage. We have a lot different types of connective tissue that is allowing for the chest wall to expand. So the chest wall, if we were to kind of show this here, let's say that I'm gonna represent the chest wall in this color here and I'm gonna represent the elasticity of the lungs and this in the surface tension the green color. What direction is it trying to pull the lungs? It's trying to pull it this way. That's what it's trying to do. It's trying to pull the lungs in this way to collapse them. Whereas the chest wall, when you're breathing, what is it trying to do? It's trying to push the chest wall out to expand the chest wall. And if it's trying to expand the chest wall, what is that doing? It's pulling this parietal pleura away from the visceral pleura. If you're pulling this actual parietal pleura away from the visceral pleura, what is that doing to this volume in here? It's increasing the volume. the volume. So the dynamic interplay between these three concepts here, the elasticity of the lungs, the surface tension, and the elasticity of the chest wall, what is the overall result of all of these? The overall result of all of these three things is that is that they're increasing, or they're attempting to, they're not necessarily doing, but they're attempting to, they're increasing thoracic cavity volume, which is that intrapleural space right there, that pleural cavity space, right? You know there's a law, Boyle, he came up with a law, and what that law is, it states that Okay, pressure, if you have a certain pressure here, let's say I call it P1. V1 is a volume, P2 is a second pressure, and then you have V2 which is the second volume, right? He says based upon this relationship, okay? based upon this relationship whenever because it's in this format whenever I increase the pressure of this reaction whatever reaction might be it's going to decrease the volume that's the relationship with Boyle's Law so Boyle's Law states That whenever there is a increase in the pressure, there will be a direct decrease in the volume. Same thing. Let's say that we actually do something opposite. Let's say that I increase the volume. Whenever I increase the volume, what is that going to do to pressure? It's going to drop the pressure. Huh. That's interesting. Because isn't the whole purpose to make this pressure negative or decrease the pressure below the intrapulmonary, have it always being a little bit lower or negative pressure? Yes. And that's the whole purpose. That's why the intrapleural pressure is negative. Again, what are those three reasons? The elasticity of the lungs. What do they want to do? Cause the lungs to snap and actually collapse. Snap back to their small size possible. Surface tension. Once they collapse the alveoli, which tries to collapse the lungs. Pushing this way. Creating a bigger volume. A potential volume space. Chest wall, elasticity of the chest wall, constantly, whenever we're inspiring it, wants to try to bring the actual chest wall out. That's what you want to. Whenever you bring air in, what do you want to do? You want to try to expand that chest wall. So the chest wall is naturally elastic and it wants to expand out this way. What is that trying to do? It's trying to pull on the parietal pleura away from the visceral pleura. But normally, you know, our chest wall, when it's not contracting, what would it actually do? It can recoil also. So because of that, sometimes what it can do, Now to say that it's only ever going this way, it prefers to be expanded, but it can have an actual recoil capability here too. Okay, so it does have a little bit of recoil capability here too. But nonetheless, the dynamic interplay between the elasticity, surface tension, and the elasticity of the chest wall play a role in maintaining this negative interpolar pressure. You know, there's actually one more thing. You know, there's lymphatic vessels in this area. Let's say that I represent this lymphatic vessels with this brown structure here. Let's say here I put a little tube in here. Here's this little tube and this brown tube right here and I'll put another one right here. This brown tube right here are lymphatic vessels. Let's say that these are lymphatic vessels. Okay so this is my lymphatic vessels. You know what's really important about this pleural cavity is that we want to make sure that there's not too much fluid accumulating out in this area. We don't want there to be too much fluid and one of the ways that we control that Okay, so here let's see here's our pleural fluid right here's our pleural fluid to prevent excessive amounts of pleural fluid from accumulating You know we have we have these little emphatic vessels from the bronchomedia stinal trunk area right that can drain this actual pleural cavity and Prevent the excessive amounts of fluid from building up because you know what happens if we build up a lot of fluid It's gonna start trying to push on the lungs right so we don't want that so again Pleural fluid is constantly being actually drained out by the lymphatic vessels to maintain a nice volume in here so it doesn't disturb the intrapleural pressure also. Okay so we got that down so again what have we covered so far? We covered visceral pleura is this little epithelial tissue layer clinging to the lung. Pleural cavity which is this potential space right consisting of a pleural fluid and we talked about the third thing which was the parietal pleura which is this layer clinging to the chest wall. Then we said there's three pressures in the lung or basically across this whole lung structure here right. Intrapulmonary pressure, which is also called the intraalveolar pressure, right? And again, we showed it by this alveoli there. It's approximately 760 millimeters of mercury. Then we said that there's a pressure right here, which is the intrapleural pressure, which is 756 millimeters of mercury. And then we said that there's an atmospheric pressure outside of the body, right? Around us. That is the atmospheric pressure, which is approximately 760. But I said we could express it another way. If I take the intrapulmonary pressure and subtract it from the atmospheric, what is that? That is zero. If I take the intrapleural pressure and subtract from the atmospheric pressure, what is that? That's negative four. Okay? And we explained why is it a negative pressure. Because the elasticity of the lungs and the surface tension, they want the lungs to collapse. They want to assume the smallest size possible, which is going to increase this actual volume of this space, potentially. Then we also said that the elasticity of the chest wall. Two things can happen. Whenever we're inspiring, the chest wall would want to expand outwards. But whenever we're resting, it wants to kind of actually... just maintain that size, but it can have a force that's kind of driving to direct inwards a little bit, right? But no matter what, the dynamic interplay between the elasticity of the lungs, the surface tension, and the elasticity of the chest wall helps to keep this volume increasing. And by Boyle's law, we said that whenever the volume is increasing, the pressure in this actual cavity is decreasing, okay? So because of this, because the thoracic cavity volume decreases, I'm sorry, because the thoracic cavity volume increased, I'm sorry, this would actually decrease the actual thoracic cavity volume, but specifically the intra, not thoracic cavity volume, but thoracic cavity pressure. So it would actually decrease the intra pleural pressure, okay, because of Boyle's law. So again, whenever you increase the volume in thoracic cavity, it's going to decrease the thoracic cavity volume pressure, but specifically that pressure that we call the thoracic cavity pressure is really the intrapleural pressure and that will decrease to about negative four. And then again we said that the pleural fluid is actually constantly being pumped out of the pleural cavity by the lymphatic vessels like the bronchomediastinal trunk to maintain a normal volume so it doesn't interfere with the actual intrapleural pressure. One more thing and then we're going to go over these actual changes of how breathing is affected here. Gravity. I mentioned gravity. Now when gravity is actually acting downwards, what happens? Let's say that I actually pretend for a second that I take the bottom of this lung here I take the bottom of this lung and I try to yank it down by gravity as I yank the bottom of this lung down by gravity it's gonna pull on the apex too so I'm gonna pull the apex farther away what part of my pulling farther away I'm pulling the visceral pleura farther away from the parietal pleura okay so as I'm yanking down at the base of this lung I'm pulling down here I'm bringing this visceral pleura closer to this parietal par But when I'm pulling, I'm also pulling on this apex here. Because remember, these are kind of closely attached, right? They're almost really like just rubbing up against one another. So when I pull down here, it starts pulling this actual visceral pleura away from that parietal pleura. So now if you think about it for a second, what's happening to this volume here when I stretch and pull that base down? What's happening to that volume? The volume here is decreasing. What does that say for the pressure? The pressure will be a little bit larger in this area. What about up here? Well, I'm pulling this down. If I'm pulling the visceral pleura away from the parietal pleura up here, what does that mean then? Well, that means that the volume up here will be a little bit greater than it was down here. So what does that mean for the pressure? The pressure will be a little bit... Lower up there. Now we're not going to specifically talk about that, but I want you guys to realize that their intrapleural pressure is not uniform throughout the entire pleural cavity. It is different. It's approximately like 758 here, 756 here, and 753 up here. Okay, but we're only going to refer to it as 756, but I do want you to realize that it isn't uniform throughout the entire pleural cavity. Okay, now we got to do another thing. that I need to mention here that is really, really important. We're not going to spend a lot of time, but I want you to understand that there is other pressures, a pressure across a wall. So for example, remember we said that this was intrapulmonary pressure. Let's denote it again with AB. This is A right here, but we're going to just denote this A here for a second. Again, intraalveolar pressure, intraalveolar pressure. I'm just denoting it here so it's close to this. This is the B pressure, which was the intrapleural pressure, and here was the C pressure. Let's say I make a line here. I have a pressure that's being exerted across these two walls. Okay, so there's a pressure that's being exerted across these two walls. Then, there's also another pressure. Let's do this one in pink. There's a pressure being exerted across the chest wall. There's a pressure being exerted across the chest wall. What are these two pressures, and why are they important? This pressure here, across this wall, which is the... difference between the intrapulmonary and intrapleural pressure. This pressure here that is across this wall, let's write it according with the color, this pressure is called the, let's write it down here, trans pulmonary pressure. That's interesting. We're going to denote this TP to make it easier. So TP is our transpulmonary pressure, okay? Alright, so that's good for right now. We're going to talk about that in just a second. Then, there's a pressure exerted across this chest wall. And it's the difference between the interpulmonary pressure and the atmospheric pressure. Okay. What is that pressure called? This pressure here is called the transthoracic pressure. It's called the transthoracic pressure. Okay. And we'll just call this one TTP. Alright, whatever, it doesn't matter. But as long as you understand that the TP is the transpulmonary pressure and the TTP is the transthoracic pressure. Okay? There is one more. I'll mention it, but we're not going to really spend a lot of time on it because it's not super, super significant here. But I will mention it quickly. It's the pressure all the way from A all the way to C. And this pressure here... is actually called the trans-respiratory pressure. I'll write it up here. Trans-respiratory pressure. Okay. So I just want to explain something real quick here. All right. So now with the trans-respiratory pressure and with this trans-thoracic pressure and trans-pulmonary pressure, what is the significance of this? Okay. Well, let's write out a little formula here. So let me actually bring this one down a little bit so we have more room. So I'm going to bring this One down here, so this is again trans-thoracic pressure, and again we denote that as TTP. Alright, so TTP here. Okay, now. Transpulmonary pressure, what do we say? We said it was the difference from the intrapulmonary A minus B. That's the difference. So what do we actually say? We're not going to say A minus B. We're going to say it's the P-pull, which is the intrapulmonary pressure, minus the B. Well B was the intrapleural pressure. So we're going to put intrapleural pressure. This is equal to the transpulmonary pressure. Okay, well what is that? Let's get a number out of this bad boy. Let's say that this is at rest. Okay, with intrapulmonary pressure, we said was about, I'm sorry, 760 millimeters of mercury. But again, we could use zero also. It wouldn't matter if you use zero. We'll do zero just for the heck of it. 0 for that one and then negative 4 for the intrapleural. Okay, let's write that down. So the intrapulmonary and again, I could have put 760 and I could have put 756 it doesn't matter here. But what we're gonna do is intrapulmonary pressure here is going to be specifically 0 millimeters of mercury and then what is it over here for this negative? So it's minus intrapleural pressure, which is negative 4. So then, if I do 0 minus minus 4, it's just I'm adding, right? I'm adding in this case, and I should actually use the units, right? I shouldn't be lazy. Let me put the units in here so I'm consistent. I'm sorry. Negative 4 millimeters of mercury. The difference in this will give me 4 millimeters of mercury. So you see how if I took 760 minus 756, it would still give me 4 millimeters of mercury. But let's even define it a little bit more. It's positive. It's not negative, it's positive. What does that mean for it to be positive? If the transpulmonary pressure is positive, that's a good thing. That means that the lungs are actually going to be able to be inflated. If it's negative, that's a bad thing. It means it's going to try to deflate. Okay, now let's do the transthoracic pressure. The transthoracic pressure, we said, was the difference across the chest wall. So it's intrapleural pressure minus the atmospheric pressure. Okay, let's do that one. So we said TTP, which is the transthoracic pressure. is equal to the, okay, B, intrapleural pressure. So I'm going to put PIP minus the atmospheric pressure, which is the pressure C, so P of the atmosphere. What does that give me? Okay, intrapleural pressure we said was negative 4, so we're going to write here, it was negative 4 millimeters of mercury, and then the atmospheric pressure is 0, 0 millimeters of mercury. Okay, so then if that's the case then trans thoracic pressure is actually just equal to the intrapleural pressure then because this is zero So what is this actually equal then this equals negative four minus zero which is negative four millimeters of mercury And so what does that mean that negative four millimeters of mercury means that it's trying to deflate That's why the chest wall because of this if you look at the actual trans thoracic pressure naturally This is actually going to want to try to come this way, right? It's not going to want to be inflated. It'll actually cause a deflating pressure. So the transthoracic pressure is a deflating pressure. Okay. So we've done transpulmonary transthoracic. There is the last one. We can mention it really quickly. And it's just, again, intraalveolar pressure right here, minus the atmospheric pressure. So if we wrote that one down just for the heck of it, it would be the intra. Pulmonary pressure, right? So trans-respiratory pressure, we'll call this one TRP. So trans-respiratory pressure is equal to the P-pull minus the P of the atmospheric pressure. Okay, well what does that equal to? That's equal to 0 minus 0. So what will this be? It'll be 0 millimeters of mercury. And again, we're doing all of this at rest. So this will be 0 millimeters of mercury. This is all at rest. We're going to compare this. to what it would look like afterwards whenever we're going to do the inspiration process. All right, so again, with all these pressures, let's quickly go through them. Transvascular pressure is the intrapulmonary pressure minus the atmospheric pressure. So therefore, it is zero millimeters of mercury. So therefore, there's no real gas flow that's moving in any direction here. And there is no pressure differences across this, okay? Transpulmonary pressure, this is a really important one. This one and transthoracic are the more important pressures. Transthoracic pressure, I'm sorry, transpulmonary pressure, the intrapulmonary minus the intrapleural and we said again you'll take this zero millimeters of mercury which was 760 again we could write like that minus the intrapleural which could either be 756 or you can write negative four it doesn't matter you're still gonna get the same number which is gonna be positive four millimeters of mercury. Again, what does that mean? That means that this is trying to expand outwards. What you want here is you want this actual lung to be able to inflate, right? You want it to be able to inflate. So positive pressure means that you're trying to inflate the structure. Now, if we look at transthoracic pressure, what's happening here? This one's a little interesting, right? Because you're taking the intrapleural pressure, subtracting from the atmospheric pressure, but what are you actually left with? You're really only left with intrapleural pressure. So if that's the case then, your transthoracic pressure is equal to your actual intrapleural pressure, negative four millimeters of mercury. So what does that mean then? It goes back to that thing that we said. It's due to this natural outward elasticity or recoil of the chest wall, right? Because that's trying to pull this, what? Parietal pleura away from the visceral pleura, which is increasing this volume. What else did we say? We said it was also due to the natural elasticity in the surface tension of the lungs, which is trying to pull this out. to pull the actual visceral pleura away from the parietal pleura. What is that doing to the volume? It's increasing the volume. And what will that do to the pressure in this area? It will decrease the pressure. And that's why this should make sense. Okay, now that we've done that, we've gone over a whole bunch of pressures and a whole bunch of different formulas and numbers. I'm sorry about that. What we're going to do is we're going to go over how is these pressures changing whenever we're going through the inspiratory process. So if you guys stick with us, go to part two. We're going to specifically see how the nervous system is affecting the actual, this whole respiratory structure here and how that's actually producing pressure differences. All right, Ninja Nerds, I'll see you in part two.

So let's go ahead and dig right in. So before we do that, we need to look at a little bit of anatomy for the lungs and a lot of the chest wall structure. So let's do that first.

So if you look here, we have two lungs, right? Right, left lung. And what's going to happen is you're going to have, you know, the actual trachea.

The trachea is going to branch off into the right and left primary bronchus, serving the actual... Lung, specifically at the smallest structural unit called the alveoli. We'll talk about that in a second. But the lung itself, each individual alveoli is making up the lung.

But if you look at the lung, it has this nice little thin epithelial tissue with a little bit of areolar connective tissue clinging on to that organ. So you see this blue layer right there? That blue layer right there, we're going to denote this layer right here. Let's call this layer one.

Okay, so layer one right there. So layer one is specifically called the actual visceral pleura. So again, this layer one is actually called the visceral pleura. Okay, that's the first layer.

Then let's keep working our way out. Now you see this space right here, this little hollow like cavity, but it has a little bit of fluid in it. This space right here, we're going to call this.

Number two here. So number two. Number two is actually this whole cavity here is actually specifically called the pleural cavity.

Now here's what's interesting about the pleural cavity. In this diagram, I'm actually showing a space. In the human body, there actually is no space.

It's actually a potential space, they call it. And the reason why is in our human body, the lungs, this visceral pleura is tethered or connected. to the actual, this pleura right here, this last one we'll talk about.

This last one here is called the parietal pleura. Let me write this one down. Again, this third one is specifically called the parietal pleura. But to come back to that thought that I was saying, remember, this visceral pleura is almost completely tethered to the parietal pleura.

And how they're tethered together and connected together is through this actual pleural cavity. What's... in the pleural cavity.

Pleural fluid. There's a little bit of like a serious like fluid in here that allows for, imagine this for a second. Let's say here I take the eraser.

The eraser is supposed to represent the visceral pleura. Here's the marker. This is supposed to represent the parietal pleura. Technically they are really really close together rubbing up against one another all the time. Now you might be saying, oh wait but if that happens all the time wouldn't that produce friction and inflammation and tissue damage?

It would. But guess what our body does to prevent that from happening? That pleural cavity is occupied by what's called a pleural fluid that we said. And what that pleural fluid does is when the actual layers are rubbing up against one another during the inhalation and expiration processes, it allows for there to be no friction or very little friction and prevents inflammation.

What happens when actually in certain situations where there is too much fluid accumulation or actually there's very little fluid accumulation, and these layers start rubbing up against one another and start causing a lot of agitation, it can produce what's called pleurisy. So that is a condition that can come about whenever there is a lot of friction developing between the parietal pleura and the visceral pleura due to maybe a decreased situation and not enough pleural fluid being produced. Okay, so again what do we have here?

We have the pleural cavity, number two, and number one we have the visceral pleura. Okay, now we need to talk about something else. We need to talk about pressures because pressures is an important topic that we need to talk about here.

Okay, there's three main pressures that we're going to talk about. Let's denote these A, B, and C. Okay, so we're going to call these pressures A, B, and C. So this is going to be pressure A, this is going to be pressure B, and this is going to be pressure C. Okay?

Pressure A, pressure B, pressure C. Pressure A, we're going to just name them first. Pressure A is actually referred to as the intrapulmonary pressure.

So it's referred to as the intrapulmonary or intraalveolar. Sometimes they call it intraalveolar pressure. Okay, and why did I say intraalveolar? Well, you really know what happens is, you know, technically whenever the trachea is coming here, it's going away to the bronchi, and then it goes secondary, tertiary, and then eventually goes to terminal bronchials, respiratory, and it branches out to these actual small structures. You see these little sacs here?

These small little like... Grape-like structures, those are called the alveoli. So technically, when I say intrapulmonary pressure, I really mean intraalveolar pressure, right?

Which is the pressure in here. So this is the A pressure, right? The pressure that we were talking about.

But I'm just blowing it up here for the sake of this video so it's very clear, right? So, intrapulmonary pressure is this one. What is this B pressure? What is the pressure here in this pleural cavity?

It's called the intrapleural pressure. Not that bad, right? Not that bad to remember.

So again, what is this pressure here? It's called the intra-plural pressure. Okay, sweet deal. And again, it's the pressure that actually will be occupied in this pleural cavity.

The last one, which is the C pressure, is the atmospheric pressure or the barometric pressure. You might have even heard of that as barometric pressure or atmospheric. They're called barometric pressure or atmospheric pressure. Now why am I saying all this stuff? Because this is going to be critical.

Once we get these actual pressures down, the numbers down, it's going to make this whole mechanics a lot easier. Okay, so now what we're going to do is we're going to give you numbers for each one of these pressures. I'm going to explain a little relationship between the two. Okay, so I'm going to write these down here. So the intrapulmonary pressure is approximately, approximately, and we're going to denote it as P pull, okay?

And P pull is just denoting that it's the intrapulmonary pressure. It is approximately 70 degrees. 760 millimeters of mercury. That's the unit that they're actually measuring it in, right?

Then this next one, intrapleural pressure. Intrapleural pressure is approximately, and we're going to denote this as PIP. So we're going to denote this as PIP, representing that it's intrapleural pressure.

Intrapleural pressure is approximately, it's always negative. We refer to it as a negative pressure. And I'll explain what that means when I mean negative pressure. Just hang in there a little bit.

Intrapolar pressure is always less than the intrapulmonary pressure. You might be like, okay, well how much? About four millimeters of mercury less than the intrapulmonary intraalveolar pressure. So what's four minus 760 is about 756. So this is approximately 756 millimeters of mercury, which again is the units for this pressure. And the last one is going to be the atmospheric pressure.

And the atmospheric pressure or the barometric pressure at sea level, at one atmosphere usually, we say is approximately about 760 millimeters of mercury. Okay. So let's write this one down. We'll put P and we'll put atm, which is atmospheric pressure. This is approximately 760 millimeters of mercury.

And again, millimeters of mercury is the unit. Sometimes they use centimeter of water in certain situations, right? Okay.

We're going to use millimeters of mercury in this situation. We're not going to use centimeters of water. Okay, now that we have all the pressures, I want to explain a little bit about these pressures. Primarily, one of the ones that bug people out a lot is the intrapleural pressure. I want to talk about this a little bit.

Before I do that, though, I want to correlate this thing I'm going to talk about. I'm going to use these terms a lot, negative and positive and zero pressures. When we compare pressures, so if it's zero pressure, negative pressure, positive pressure, we compare it to the atmosphere.

Okay, so for example, the atmospheric pressure is... 760 millimeters of mercury, all right? What is the intrapulmonary pressure? 760 millimeters of mercury. What is 760 minus 760?

It's zero. So this is called, this is actually technically, we can also write that this pressure here, this intrapulmonary pressure is also zero millimeters of mercury, right? And that's because, so sometimes, just so you know, these can be interchangeable. I could put 760 or I could put zero. All that means is that it's equal to the atmospheric pressure, okay?

Okay, now let's compare intrapleural pressure to atmospheric pressure. Okay, 760 minus 756 is 4 millimeters of mercury. But, when we think about this one, okay, what we're actually doing is, I should actually rephrase this.

When you're subtracting, you're subtracting intra-pulmonary minus atmospheric. And you're subtracting intra-pleural from atmospheric. So, if I'm actually subtracting 760 from 760, it's 0. But, if I subtract 756 minus 760, what is that? that that's negative four okay sorry about that max up right all right so now this intrapulmonary pressure technically we could also write that it is actually negative four millimeters of mercury Okay, now that we have these numbers out of the way right so this is a negative pressure This is a zero pressure here. I want to explain why this is negative because this this bugs people out Okay, so let me take intrapleural pressure down here.

I want there's three reasons why intrapleural pressure is actually negative So let me explain this real quick so intra Pleural Pressure Or as we denote it here, we denote it as the PIP. I'll refer to this a lot, right? So it's a negative pressure.

There's three reasons why this is a negative pressure. Okay, first reason is the elasticity of the lungs. Okay, so the first reason is the natural elasticity of the lungs. Second reason is what's called surface tension. We'll have another video specifically on surface tension and surfactant.

But this one is going to be surface tension. And then the last thing is going to be the elasticity of the chest wall. So the last thing is going to be the elasticity of the chest wall. Okay, let me explain what I mean by this. And there's also one last thing that I'll mention, and it's not with respect to this, it's due to the differences in the intrapleural pressure throughout the intrapleural cavity, and this is due to gravity.

I'll mention this last one, okay? But again, this is not really one of the things that's contributing to it. It's contributing to a difference in the pressures. So it can contribute to the differences in the pressure.

I'll explain what I mean by that because you can see that the pressure, interpolar pressure, can be different here, here, and here. And I'll explain that. First off, elasticity of the lungs and the surface tension.

We're going to group those together for a second and let me explain why. Now, first off, what is the definition of elastance? How would you define elasticity?

Elasticity is whenever you try to stretch something, right? It doesn't want to be stretched. It wants to resist the actual desire to be stretched. It wants to recoil. It always wants to assume the smallest size possible.

That's what elasticity is. Think about this for a second. Where is this elasticity coming into play?

Well, technically, Whenever the lungs want to re-quilt, what are they actually doing? Imagine, again, I told you that imagine the parietal pleura and the visceral pleura as actually close together, as actually touching. When I try for my lungs to actually deflate, if I try to deflate them, what is it going to do to the visceral pleura?

It's going to pull it away. As it pulls it away, because it's trying to deflate, it's trying to get smaller. As the lungs is trying to get smaller, it's pulling away from, pulling this visceral pleura away from the parietal pleura. Now, Let's do surface tension. What is surface tension doing?

Surface tension is this concept that because of the water molecules, this interaction between the air and the alveoli and the water molecules, it causes this tension at the air-water interface. And the whole thing is that the alveoli wants to collapse. It wants to assume the smallest size possible.

So in other words, same thing. What's the overall purpose? The lungs are trying to pull this visceral pleura away from the parietal pleura. Okay. Well, that's trying to collapse the lungs and increase this volume.

volume here. Okay, that's one thing that's happening. The next thing that's happening is the elasticity of the chest wall. Okay, what's the chest wall trying to do?

Well, you know normally our chest wall is decently elastic. There's a lot of, you know, the coastal cartilage. We have a lot different types of connective tissue that is allowing for the chest wall to expand.

So the chest wall, if we were to kind of show this here, let's say that I'm gonna represent the chest wall in this color here and I'm gonna represent the elasticity of the lungs and this in the surface tension the green color. What direction is it trying to pull the lungs? It's trying to pull it this way.

That's what it's trying to do. It's trying to pull the lungs in this way to collapse them. Whereas the chest wall, when you're breathing, what is it trying to do?

It's trying to push the chest wall out to expand the chest wall. And if it's trying to expand the chest wall, what is that doing? It's pulling this parietal pleura away from the visceral pleura.

If you're pulling this actual parietal pleura away from the visceral pleura, what is that doing to this volume in here? It's increasing the volume. the volume.

So the dynamic interplay between these three concepts here, the elasticity of the lungs, the surface tension, and the elasticity of the chest wall, what is the overall result of all of these? The overall result of all of these three things is that is that they're increasing, or they're attempting to, they're not necessarily doing, but they're attempting to, they're increasing thoracic cavity volume, which is that intrapleural space right there, that pleural cavity space, right? You know there's a law, Boyle, he came up with a law, and what that law is, it states that Okay, pressure, if you have a certain pressure here, let's say I call it P1.

V1 is a volume, P2 is a second pressure, and then you have V2 which is the second volume, right? He says based upon this relationship, okay? based upon this relationship whenever because it's in this format whenever I increase the pressure of this reaction whatever reaction might be it's going to decrease the volume that's the relationship with Boyle's Law so Boyle's Law states That whenever there is a increase in the pressure, there will be a direct decrease in the volume.

Same thing. Let's say that we actually do something opposite. Let's say that I increase the volume.

Whenever I increase the volume, what is that going to do to pressure? It's going to drop the pressure. Huh.

That's interesting. Because isn't the whole purpose to make this pressure negative or decrease the pressure below the intrapulmonary, have it always being a little bit lower or negative pressure? Yes.

And that's the whole purpose. That's why the intrapleural pressure is negative. Again, what are those three reasons? The elasticity of the lungs. What do they want to do?

Cause the lungs to snap and actually collapse. Snap back to their small size possible. Surface tension. Once they collapse the alveoli, which tries to collapse the lungs.

Pushing this way. Creating a bigger volume. A potential volume space. Chest wall, elasticity of the chest wall, constantly, whenever we're inspiring it, wants to try to bring the actual chest wall out.

That's what you want to. Whenever you bring air in, what do you want to do? You want to try to expand that chest wall.

So the chest wall is naturally elastic and it wants to expand out this way. What is that trying to do? It's trying to pull on the parietal pleura away from the visceral pleura. But normally, you know, our chest wall, when it's not contracting, what would it actually do? It can recoil also.

So because of that, sometimes what it can do, Now to say that it's only ever going this way, it prefers to be expanded, but it can have an actual recoil capability here too. Okay, so it does have a little bit of recoil capability here too. But nonetheless, the dynamic interplay between the elasticity, surface tension, and the elasticity of the chest wall play a role in maintaining this negative interpolar pressure.

You know, there's actually one more thing. You know, there's lymphatic vessels in this area. Let's say that I represent this lymphatic vessels with this brown structure here. Let's say here I put a little tube in here.

Here's this little tube and this brown tube right here and I'll put another one right here. This brown tube right here are lymphatic vessels. Let's say that these are lymphatic vessels.

Okay so this is my lymphatic vessels. You know what's really important about this pleural cavity is that we want to make sure that there's not too much fluid accumulating out in this area. We don't want there to be too much fluid and one of the ways that we control that Okay, so here let's see here's our pleural fluid right here's our pleural fluid to prevent excessive amounts of pleural fluid from accumulating You know we have we have these little emphatic vessels from the bronchomedia stinal trunk area right that can drain this actual pleural cavity and Prevent the excessive amounts of fluid from building up because you know what happens if we build up a lot of fluid It's gonna start trying to push on the lungs right so we don't want that so again Pleural fluid is constantly being actually drained out by the lymphatic vessels to maintain a nice volume in here so it doesn't disturb the intrapleural pressure also.

Okay so we got that down so again what have we covered so far? We covered visceral pleura is this little epithelial tissue layer clinging to the lung. Pleural cavity which is this potential space right consisting of a pleural fluid and we talked about the third thing which was the parietal pleura which is this layer clinging to the chest wall. Then we said there's three pressures in the lung or basically across this whole lung structure here right. Intrapulmonary pressure, which is also called the intraalveolar pressure, right?

And again, we showed it by this alveoli there. It's approximately 760 millimeters of mercury. Then we said that there's a pressure right here, which is the intrapleural pressure, which is 756 millimeters of mercury. And then we said that there's an atmospheric pressure outside of the body, right?

Around us. That is the atmospheric pressure, which is approximately 760. But I said we could express it another way. If I take the intrapulmonary pressure and subtract it from the atmospheric, what is that? That is zero. If I take the intrapleural pressure and subtract from the atmospheric pressure, what is that?

That's negative four. Okay? And we explained why is it a negative pressure.

Because the elasticity of the lungs and the surface tension, they want the lungs to collapse. They want to assume the smallest size possible, which is going to increase this actual volume of this space, potentially. Then we also said that the elasticity of the chest wall. Two things can happen.

Whenever we're inspiring, the chest wall would want to expand outwards. But whenever we're resting, it wants to kind of actually... just maintain that size, but it can have a force that's kind of driving to direct inwards a little bit, right? But no matter what, the dynamic interplay between the elasticity of the lungs, the surface tension, and the elasticity of the chest wall helps to keep this volume increasing. And by Boyle's law, we said that whenever the volume is increasing, the pressure in this actual cavity is decreasing, okay?

So because of this, because the thoracic cavity volume decreases, I'm sorry, because the thoracic cavity volume increased, I'm sorry, this would actually decrease the actual thoracic cavity volume, but specifically the intra, not thoracic cavity volume, but thoracic cavity pressure. So it would actually decrease the intra pleural pressure, okay, because of Boyle's law. So again, whenever you increase the volume in thoracic cavity, it's going to decrease the thoracic cavity volume pressure, but specifically that pressure that we call the thoracic cavity pressure is really the intrapleural pressure and that will decrease to about negative four.

And then again we said that the pleural fluid is actually constantly being pumped out of the pleural cavity by the lymphatic vessels like the bronchomediastinal trunk to maintain a normal volume so it doesn't interfere with the actual intrapleural pressure. One more thing and then we're going to go over these actual changes of how breathing is affected here. Gravity. I mentioned gravity. Now when gravity is actually acting downwards, what happens?

Let's say that I actually pretend for a second that I take the bottom of this lung here I take the bottom of this lung and I try to yank it down by gravity as I yank the bottom of this lung down by gravity it's gonna pull on the apex too so I'm gonna pull the apex farther away what part of my pulling farther away I'm pulling the visceral pleura farther away from the parietal pleura okay so as I'm yanking down at the base of this lung I'm pulling down here I'm bringing this visceral pleura closer to this parietal par But when I'm pulling, I'm also pulling on this apex here. Because remember, these are kind of closely attached, right? They're almost really like just rubbing up against one another. So when I pull down here, it starts pulling this actual visceral pleura away from that parietal pleura. So now if you think about it for a second, what's happening to this volume here when I stretch and pull that base down?

What's happening to that volume? The volume here is decreasing. What does that say for the pressure? The pressure will be a little bit larger in this area. What about up here?

Well, I'm pulling this down. If I'm pulling the visceral pleura away from the parietal pleura up here, what does that mean then? Well, that means that the volume up here will be a little bit greater than it was down here. So what does that mean for the pressure?

The pressure will be a little bit... Lower up there. Now we're not going to specifically talk about that, but I want you guys to realize that their intrapleural pressure is not uniform throughout the entire pleural cavity. It is different.

It's approximately like 758 here, 756 here, and 753 up here. Okay, but we're only going to refer to it as 756, but I do want you to realize that it isn't uniform throughout the entire pleural cavity. Okay, now we got to do another thing.

that I need to mention here that is really, really important. We're not going to spend a lot of time, but I want you to understand that there is other pressures, a pressure across a wall. So for example, remember we said that this was intrapulmonary pressure. Let's denote it again with AB.

This is A right here, but we're going to just denote this A here for a second. Again, intraalveolar pressure, intraalveolar pressure. I'm just denoting it here so it's close to this. This is the B pressure, which was the intrapleural pressure, and here was the C pressure.

Let's say I make a line here. I have a pressure that's being exerted across these two walls. Okay, so there's a pressure that's being exerted across these two walls. Then, there's also another pressure.

Let's do this one in pink. There's a pressure being exerted across the chest wall. There's a pressure being exerted across the chest wall. What are these two pressures, and why are they important? This pressure here, across this wall, which is the...

difference between the intrapulmonary and intrapleural pressure. This pressure here that is across this wall, let's write it according with the color, this pressure is called the, let's write it down here, trans pulmonary pressure. That's interesting.

We're going to denote this TP to make it easier. So TP is our transpulmonary pressure, okay? Alright, so that's good for right now. We're going to talk about that in just a second.

Then, there's a pressure exerted across this chest wall. And it's the difference between the interpulmonary pressure and the atmospheric pressure. Okay. What is that pressure called? This pressure here is called the transthoracic pressure.

It's called the transthoracic pressure. Okay. And we'll just call this one TTP.

Alright, whatever, it doesn't matter. But as long as you understand that the TP is the transpulmonary pressure and the TTP is the transthoracic pressure. Okay?

There is one more. I'll mention it, but we're not going to really spend a lot of time on it because it's not super, super significant here. But I will mention it quickly. It's the pressure all the way from A all the way to C.

And this pressure here... is actually called the trans-respiratory pressure. I'll write it up here.

Trans-respiratory pressure. Okay. So I just want to explain something real quick here.

All right. So now with the trans-respiratory pressure and with this trans-thoracic pressure and trans-pulmonary pressure, what is the significance of this? Okay.

Well, let's write out a little formula here. So let me actually bring this one down a little bit so we have more room. So I'm going to bring this One down here, so this is again trans-thoracic pressure, and again we denote that as TTP. Alright, so TTP here. Okay, now.

Transpulmonary pressure, what do we say? We said it was the difference from the intrapulmonary A minus B. That's the difference. So what do we actually say?

We're not going to say A minus B. We're going to say it's the P-pull, which is the intrapulmonary pressure, minus the B. Well B was the intrapleural pressure.

So we're going to put intrapleural pressure. This is equal to the transpulmonary pressure. Okay, well what is that? Let's get a number out of this bad boy. Let's say that this is at rest.

Okay, with intrapulmonary pressure, we said was about, I'm sorry, 760 millimeters of mercury. But again, we could use zero also. It wouldn't matter if you use zero.

We'll do zero just for the heck of it. 0 for that one and then negative 4 for the intrapleural. Okay, let's write that down.

So the intrapulmonary and again, I could have put 760 and I could have put 756 it doesn't matter here. But what we're gonna do is intrapulmonary pressure here is going to be specifically 0 millimeters of mercury and then what is it over here for this negative? So it's minus intrapleural pressure, which is negative 4. So then, if I do 0 minus minus 4, it's just I'm adding, right? I'm adding in this case, and I should actually use the units, right?

I shouldn't be lazy. Let me put the units in here so I'm consistent. I'm sorry.

Negative 4 millimeters of mercury. The difference in this will give me 4 millimeters of mercury. So you see how if I took 760 minus 756, it would still give me 4 millimeters of mercury.

But let's even define it a little bit more. It's positive. It's not negative, it's positive.

What does that mean for it to be positive? If the transpulmonary pressure is positive, that's a good thing. That means that the lungs are actually going to be able to be inflated. If it's negative, that's a bad thing. It means it's going to try to deflate.

Okay, now let's do the transthoracic pressure. The transthoracic pressure, we said, was the difference across the chest wall. So it's intrapleural pressure minus the atmospheric pressure.

Okay, let's do that one. So we said TTP, which is the transthoracic pressure. is equal to the, okay, B, intrapleural pressure. So I'm going to put PIP minus the atmospheric pressure, which is the pressure C, so P of the atmosphere. What does that give me?

Okay, intrapleural pressure we said was negative 4, so we're going to write here, it was negative 4 millimeters of mercury, and then the atmospheric pressure is 0, 0 millimeters of mercury. Okay, so then if that's the case then trans thoracic pressure is actually just equal to the intrapleural pressure then because this is zero So what is this actually equal then this equals negative four minus zero which is negative four millimeters of mercury And so what does that mean that negative four millimeters of mercury means that it's trying to deflate That's why the chest wall because of this if you look at the actual trans thoracic pressure naturally This is actually going to want to try to come this way, right? It's not going to want to be inflated. It'll actually cause a deflating pressure. So the transthoracic pressure is a deflating pressure.

Okay. So we've done transpulmonary transthoracic. There is the last one.

We can mention it really quickly. And it's just, again, intraalveolar pressure right here, minus the atmospheric pressure. So if we wrote that one down just for the heck of it, it would be the intra.

Pulmonary pressure, right? So trans-respiratory pressure, we'll call this one TRP. So trans-respiratory pressure is equal to the P-pull minus the P of the atmospheric pressure. Okay, well what does that equal to? That's equal to 0 minus 0. So what will this be?

It'll be 0 millimeters of mercury. And again, we're doing all of this at rest. So this will be 0 millimeters of mercury. This is all at rest.

We're going to compare this. to what it would look like afterwards whenever we're going to do the inspiration process. All right, so again, with all these pressures, let's quickly go through them. Transvascular pressure is the intrapulmonary pressure minus the atmospheric pressure. So therefore, it is zero millimeters of mercury.

So therefore, there's no real gas flow that's moving in any direction here. And there is no pressure differences across this, okay? Transpulmonary pressure, this is a really important one. This one and transthoracic are the more important pressures. Transthoracic pressure, I'm sorry, transpulmonary pressure, the intrapulmonary minus the intrapleural and we said again you'll take this zero millimeters of mercury which was 760 again we could write like that minus the intrapleural which could either be 756 or you can write negative four it doesn't matter you're still gonna get the same number which is gonna be positive four millimeters of mercury.

Again, what does that mean? That means that this is trying to expand outwards. What you want here is you want this actual lung to be able to inflate, right?

You want it to be able to inflate. So positive pressure means that you're trying to inflate the structure. Now, if we look at transthoracic pressure, what's happening here?

This one's a little interesting, right? Because you're taking the intrapleural pressure, subtracting from the atmospheric pressure, but what are you actually left with? You're really only left with intrapleural pressure.

So if that's the case then, your transthoracic pressure is equal to your actual intrapleural pressure, negative four millimeters of mercury. So what does that mean then? It goes back to that thing that we said.

It's due to this natural outward elasticity or recoil of the chest wall, right? Because that's trying to pull this, what? Parietal pleura away from the visceral pleura, which is increasing this volume.

What else did we say? We said it was also due to the natural elasticity in the surface tension of the lungs, which is trying to pull this out. to pull the actual visceral pleura away from the parietal pleura. What is that doing to the volume? It's increasing the volume.

And what will that do to the pressure in this area? It will decrease the pressure. And that's why this should make sense.

Okay, now that we've done that, we've gone over a whole bunch of pressures and a whole bunch of different formulas and numbers. I'm sorry about that. What we're going to do is we're going to go over how is these pressures changing whenever we're going through the inspiratory process. So if you guys stick with us, go to part two. We're going to specifically see how the nervous system is affecting the actual, this whole respiratory structure here and how that's actually producing pressure differences.

All right, Ninja Nerds, I'll see you in part two.

Transcript for:Understanding the Mechanics of Breathing

Transcript for:
Understanding the Mechanics of Breathing