All right, ninja nerds. In this video, we're going to talk about the mechanics of breathing. So, this can be a tough topic for certain people to understand, especially with the pressures. So, we're going to do our best here at Ninja 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 the smallest structural unit called the alvoli. We'll talk about that in a second. But the lung itself, each individual alvoli 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 aerol 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 plura. So again, this layer one is actually called the visceral plura. 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 plural cavity. Now, here's what's interesting about the plural 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 plura is tethered or connected to the actual this plura right here. This last one we'll talk about this last one here is called the parietal plura. Let me write this one down again. This third one is specifically called the parietal plura. But to come back to that thought that I was saying, remember this visceral plura is almost completely tethered to the parietal plura. And how they're tethered together and connected together is through this actual plural cavity. What's in the plural cavity? Plural fluid. There's a little bit of like a cirrus like fluid in here that allows for imagine this for a second. Let's say here I take the eraser. This eraser is supposed to represent the visceral plura. Here's the marker. This is supposed to represent the parietal plura. 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 plural cavity is occupied by what's called a plural fluid that we said. And what that plural fluid does is when the actual layers are rubbing up against one another during the inhalation 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 puricy. So that is a condition that can come about whenever there is a lot of friction developing between the parietal plura and the visceral plura due to maybe a decreased situation and not enough plural fluid being produced. Okay. So again what do we have here? We have the plural cavity number two and number one we have the visceral plural. 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 have 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 intraulmonary pressure. So it's referred to as the intra pulmonary or intraalvolar. Sometimes they call it intraalvolar pressure. Okay. And then why did I say intraalvolar? Well, you really know what happens is you know technically whenever the trachea is coming here it's giving way 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 sacks here these small little like grape-like structures those are called the alvoli. So technically when I say intraulmonary pressure I really mean intraalvolar 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 intraulmonary pressure is this one. What is this B pressure? What is the pressure here in this plural cavity? It's called the intraplural 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 that pressure that actually will be occupied in this plural cavity. The last one which is the C pressure is the atmospheric pressure or the barometric pressure. You might have even heard of that u as barometric pressure or atmospheric it call uh 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 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 intraulmonary pressure is approximately approximately and we're going to denote it as P pull. Okay. And Pole is just denoting that it's the intraulmonary pressure. It is approximately 760 millimeters of mercury. That's the unit that they're actually measuring it in. Right? Then this next one, intraplural pressure. Intraplural 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 intraplural pressure. Intraplural pressure is approximately it's always negative. We refer to it as a negative pressure. And I'll I'll explain what that means when I mean negative pressure. So hang in there a little bit. Intraplural pressure is always less than the intraulmonary pressure. You might be like, okay, well how much? About 4 millimeters of mercury less than the intra pulmonary intravolar pressure. So what's uh 4 - 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. The atmospheric pressure or the barometric pressure is at sea level at one atmosphere usually and we say is approximately about 760 mm 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 as 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, 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 intra plural 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 mm of mercury right what is the intraulmonary pressure 760 mm of mercury what is 760us 760 it's zero so this is called this is actually technically we can also write that this pressure here this intraulmonary pressure is also 0 millm 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. Now, let's compare intraplural pressure to atmospheric pressure. Okay. 760US 756 is 4 millime of mercury. But it is a lot. 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 intraulmonary minus atmospheric and you're subtracting intraplural from atmospheric. So, if I'm actually subtracting 760 from 760, it's zero. But if I subtract 756 minus 760, what is that? That's -4. Okay, sorry about that mess up. Right. All right. So now this intraulmonary pressure technically we could also write that it is actually -4 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 intraplural pressure down here. I there's three reasons why intra plural pressure is actually negative. So let me explain this real quick. So intra plural pressure or as we denote it here we denote it as as the P IP. I'll refer to this a lot. Right? So it's a negative pressure. There is 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 intraoral pressure throughout the entropal 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. Okay. 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 in plural pressure could 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, what 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 recoil, what are they actually doing? Imagine, again, I told you that imagine the parietal plura and the visceral plura as actually close together. They're 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 part? 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 are trying to get smaller, it's pulling away from pulling this visceral plural away from the parietal plural. 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 alvoli and the water molecules, it causes this tension at the air water interface. And the whole thing is is that the alvoli 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 plura away from the parietal plura. Okay, well that's trying to collapse the lungs and increase this this 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 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 going to represent the chest wall in this color here, and I'm going to represent the elasticity of the lungs in 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 plura away from the visceral plura. If you're pulling this actual parietal plura away from the visceral plura, what is that doing to this volume in here? it's increasing 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 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 intra plural space right there that plural cavity space right you know there's a a law boil he came up with a law you know what that law is it states that okay pressure if you have a 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 uh volume Okay, he says based upon this relationship, okay, based upon this relationship, whenever because it's it's in this format, whenever I increase the pressure of this reaction of whatever reaction it might be, it's going to decrease the volume. That's the relationship with Boil's law. So, Boil'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 intraulmonary have it always being a little bit lower or negative pressure? Yes. And that's the whole purpose. That's why the intraplural pressure is negative. Again, what are those three reasons? The elasticity lungs, what do they want to do? cause the lungs to snap and and actually collapse. Snap back to their smallest size possible. Surface tension wants to collapse the alvola 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 plura away from the visceral plura. 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, you know, 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 plural 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 say here's our plural fluid, right? Here's our plural fluid. To prevent excessive amounts of plural fluid from accumulating, you know what we have? We have these little lymphatic vessels from the bronco media trunk area, right? that can drain this actual plural 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 going to start trying to push on the lungs, right? So, we don't want that. So, again, plural fluid is constantly being actually drained out by lymphatic vessels to maintain a nice volume in here so it doesn't disturb the intraplural pressure also. Okay, so we got that down. So again, what have we covered so far? We covered visceral plura is this little epithelial tissue layer clinging to the lung. plural cavity which is this potential space right consisting of a plural fluid and we talked about the third thing which was the parietal plur 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 intraulmonary pressure which is also called the intraalvolar pressure right and again we showed it by this alvoli there it's approximately 760 mm of mercury then we said that there's a pressure right here which is the intraplural pressure which is 756 millm 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 intraulmonary pressure and subtract it from the atmospheric what is that that is zero if I take the intraural pressure and subtract it from the atmospheric pressure what is that that's -4 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 Boil'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 plural pressure okay because of boil'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 intraplural pressure and that'll decrease to about4. And then again we said that the plural fluid is actually constantly being pumped out of the plural cavity by the lymphatic vessels like the bronco mediainal trunk to maintain a normal volume so it doesn't interfere with the actual intraplural 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 going to pull on the apex, too. So, I'm going to pull the apex farther away. What part am I pulling farther away? I'm pulling the visceral plura farther away from the parietal plura. Okay? So, as I'm yanking down at the base of this lung, I'm pulling down here. I'm bringing this visceral plura closer to this parietal plura. 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 plur away from that parietal plura. 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 plur away from the parietal plur 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 there intraplural pressure is not uniform throughout the entire plural 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 plural 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 intraulmonary 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, intravular pressure, intravial pressure. I'm just denoting it here. So, it's close to this. This is the B pressure, which was the intra plural 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 intraulmonary and the intraplural 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. All right. 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 interplural pressure and the atmospheric pressure. Okay, what is that pressure called? This pressure here is called the transthoracic pressure. It's called the trans thoracic pressure. Okay. And we'll just call this one TTP. All right, 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 uh 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 transpiratory 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 transpiratory pressure and with this transthoracic pressure and transpulmonary pressure, how what is the significance of this? Okay, well let's write out a little uh 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. Okay. So this is again transthoracic pressure and again we denote as that as TTP right so TTP here okay now transpulmonary pressure what do we say we said it was the difference from the intraulmonary 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 intraulmonary pressure minus the B well B was the intra plural pressure. So we're going to put intra plural 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 interpulmonary pressure we said was about I'm sorry, uh 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. Zero for that one and then -4 for the intra plural. Okay, let's write that down. So the intraulmonary and again I could have put 760 and I could have put um four uh I mean 756 it doesn't matter here but what we're going to do is intraulmonary pressure here is going to be specifically 0 millm of mercury and then what is it over here for this negative so it's minus intraplural pressure which is -4 so then if I do 0 -4 it's just I'm adding right I'm adding in this case and I should use the units, right? I shouldn't be uh lazy. Let me put the units in here so I'm consistent. I'm sorry. -4 millimeters of mercury. The difference in this will give me 4 millime of mercury. So you see how if I took 760 minus 756, it would still give me 4 millime of mercury. But let's even define that 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 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 intraplural 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 intra plural pressure. So I'm going to put P IP minus the atmospheric pressure which is the pressure C. So P of the atmosphere. What does that give me? Okay, intraplural pressure we said was -4. So we're going to write here it was -4 millimeters of mercury and then the atmospheric pressure is 0 millimeters of mercury. Okay. So then if that's the case then transthoracic pressure is actually just equal to the interplural pressure then because this is zero. So what does this actually equal then? This equals4 - 0 which is -4 mm of mercury. And so what does that mean then?4 millm of mercury means that it's trying to deflate. That's why the chest wall because of this if you look at the actual transthoracic 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 will 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. Uh we can mention it really quickly. Um and it's just again intraalvolar pressure right here minus the atmospheric pressure. So if we wrote that one down just for the heck of it, it would be the intraulmonary pressure, right? So trans respiratory pressure. We'll call this one TRP. So trans respiratory pressure is equal to the P pole minus the P of the atmospheric pressure. Okay. Well, what is 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 zero 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 inspir inspiration process. All right. So again with all these pressures let's quickly go through them. Trans respiratory pressure is the intra pulmonary pressure minus the atmospheric pressure. So therefore it is 0 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 is the intraulmonary minus the inplural. And we said again you'll take this 0 millm of mercury which was 760 again we could write it like that minus the intra plural which could either be 756 or you could write4 it doesn't matter you're still going to get the same number which is going to be positive 4 mm of mercury again what does that mean that means that this is trying to expand outwards that that you want 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 intra plural pressure, subtracting it from the atmospheric pressure. But what do you really what are you actually left with? You're really only left with intraplural pressure. So, if that's the case, then your transthoracic pressure is equal to your actual interplural pressure4 millimeters of mercury. So, what does that mean then? It goes back to that thing that we said is due to this natural outward elasticity or recoil of the chest wall, right? Because that's trying to pull this what parietal plura away from the visceral plura which is increasing this volume. What else did we say? We said it was also due to the natural elasticity and the surface tension of the lungs which is trying to pull the actual visceral plural away from the parietal plura. 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, ninj. I'll see you in part two.