Respiratory | Mechanics of Breathing: Pressure Changes | Part 1

I'm engineers 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 and engineered science to make sense of that so it's going to 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 trach 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 allo lives 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 just blue layer right there that blue layer right there we're

going to denote this layer right here let's call this layer 1 ok so layer 1 right there so layer 1 is specifically called the actual visceral pleura so again this layer 1 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 2 here so number 2 number 2 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 sclera 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 tool or 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 there's a razor 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 I guess what our body does to prevent that from happening that pleural cavity is occupiable it'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 exploration 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 fuel accumulation and these layers start rubbing up against one another and start causing a lot of agitation it can reduce 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 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 pressure 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 called 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 press your 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 intra pulmonary or intra alveolar sometimes they'll enter alveolar pressure okay and why did I say intra alveolar well you really know what happens is you know technically whenever the trachea is coming here it's getting away to the bronchi and then it goes secondary tertiary and then eventually goes to terminal bronchioles respiratory and it branches out to these actual small structures you see these little sacs here you smell a little like grape like structures those are called the alveoli so technically when I say inter pulmonary pressure I really mean enter alveolar 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 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 that's not bad to remember so again what is this pressure here it's called the intra pleural pressure okay sweet deal and again it's a pressure that actually we occupied in this pleural

cavity the last one which is the C pressure is the atmospheric pressure or the barometric pressure you might even heard that as barometric pressure or atmospheric so-called Bretta barometric pressure 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 then 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 gotta explain a little relationship between the two okay so I'm

going to write these down here so the entry of pulmonary pressure is approximately approximately we're going to denote it as p-pull okay and people is just the noting that's the intra pulmonary pressure it is approximately 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 is P I P so we're going to denote this is p IP representing that it's intrapleural pressure intrapleural pressure is approximately is always negative we refer to it as a negative pressure

and i'll explain what that means when I mean negative pressure hang in there a little bit intrapleural pressure is always less than the intrapulmonary pressure you might be like okay well how much about 4 millimeters of mercury less than the intra pulmonary and Traveller pressure so what's 4 - 760 is about 756 so this is approximately 756 millimeters of mercury which again those are the units for this pressure and the last one is going to be the atmospheric pressure the atmospheric pressure the barometric pressure at sea level at one atmosphere usually and 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 again millimeters of mercury is the unit sometimes they use centimeter of water at certain situations right okay we're going to use millimeters of mercury in the situation I'm not going to send me to the 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

intrapleural pressure I want to talk about this a little bit before I do that though I want to correlate this thing when we 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 - 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 now let's compare intrapleural pressure to atmospheric pressure okay 760 - 756 is four millimeters 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 intrapulmonary - atmospheric and you're subtracting intrapleural

from atmospheric so if I'm actually subtracting 760 from 760 at zero but if I subtract 756 - 760 what is that that's negative 4 ok sorry about that max all right all right so now this intrapulmonary pressure technically we could also write it is actually negative 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 bugs people out okay let me take intrapleural pressure down here 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 as V P IPL 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 will 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 Interpol 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 the differences in the pressure I'll explain what I mean by that because you can see that the pressure intrapleural pressure could be different here here in here I'll explain that first off elasticity of the lungs in 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 the last things 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 pleura in the visceral pleura is actually close together 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 time trying to deflate it 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 a surface tension doing surface tension is this concept that because of the water molecules this interaction between the air in the alveoli and the water molecules it causes this tension at the air water interface and the whole thing is is that the alveoli wants to collapse it wants to assume the small size possible so another 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 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 costal 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 going to represent the chest wall and this collar here and I'm going to represent the elasticity of the lungs and this and the surface tension the green color what direction is it trying to pull lungs is trying to pull it this way that's what it's trying to do is 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 so the dynamic interplay between these three concepts here the elasticity lungs the surface tension and the elasticity of the chest wall what is the overall result of all of these the overall results 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 intrapleural space right there that pleural cavity space right the others of 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 a v2 which is the second volume right 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

whatever reaction it 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 opposites let's say that I increase the volume whenever I increase the volume what is I going to do the pressure it's going to drop the pressure oh 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 one of those three reasons the elasticity loans where they want to do cause the lungs to snap and D and actually collapse that back to their small size possible surface tension wants to collapse the alveoli which tries to collapse the lungs pushing this way creating a bigger volume of potential volume space chest wall the last tasting 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 area and what do you want to do you want to try to expand that chest wall so the chest wall is natural elastic and it wants to express 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 in our chest wall when it's not contracting what would it actually do it can wreak low also so because of that sometimes what it can do you know just 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 will play a role in maintaining this negative intrapleural pressure maybe 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 there's 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 the 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 on 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 plural flow from accumulating you know we have

we have these little lymphatic vessels from the bronco mediastinal 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 pleural fluid is constantly being actually drained out by learn Phatak 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 do we covered

so far recovered visceral pleura is this little epithelial tissue layer clinging to lung pleural cavity which is this potential space right consisting of a pleural fluid and we talked about the third thing which is 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 intra alveolar 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 here

which is the intrapleural pressure which is 756 millimeters of mercury and then we said 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 intra pulmonary 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 explain why is it a negative pressure because the elasticity of the lungs in the surface

tension they want the lungs to collapse they want to assume the small size possible which is going to increase this actual volume of this space potentially then we also said that the elastic is a 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 trying to direct inwards a little bit right but no matter what the dynamic interplay between the elasticity 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 we've actually decrease T plural pressure okay because the Boyle's law so again whenever you increase the volume and thrash the 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 blowing fatik vessels like the bronco mediastinal trunk to maintain a normal volume so it doesn't interfere with the actual intrapleural pressure one more thing and then were 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 long-hair I take the bottom of this long 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 - so I want to 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 long I'm pulling down here I'm

bringing this visceral pleura closer to this product apart 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 I pull down here it starts pulling this actual visceral pleura way from that private aura 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 I bully 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 that what 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 intrapleural pressure is not uniform throughout the entire pleural cavity

it is different it's approximately like 758 here 756 here in 753 up here we're only going to refer to at 7:56 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 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 a B this

is a right here but we're going to just denote this a here for a second again entry I'll be able to pressure and travel pressure I'm just to noting in here so it's close to this this is the B pressure which was the intrapleural pressure and here was the seed 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 observed 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 the intrapleural pressure this pressure here that is across this wall let's write it according with the color this pressure is called B let's write it down here trans pulmonary pressure that's interesting or you have to note this TP to make it easier so TP there's no 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 intrapleural pressure in the atmospheric pressure okay what is that pressure called this pressure here is called the trans thoracic pressure it's called the trans thoracic 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 transfer Rasik pressure okay there is one more unmentionable we're not going to really spend a lot of time on 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 transthoracic 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 I'm going to bring this one down here so this is again trans thoracic pressure and again we denote as that is TTP all right so TTP here okay now transpulmonary pressure what do we say we said it was the difference from the intra pulmonary 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 B P pull which is the intra pulmonary pressure minus the B will be was the intrapleural pressure so we're going to put intra plural pressure this

is equal to the trans pulmonary 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 wouldn't matter if you use your we'll do zero just for the heck of it zero for that one and then negative 4 for the intrapleural okay let's write that down so the intrapulmonary again I could have put 760 and I could have put 4/7 756 it doesn't matter but

what we're going to do is enter pulmonary pressure here is going to be specifically zero let me do some mercury and then what is it over here for this negative so it's minus intrapleural pressure which is negative four 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 unit's right I shouldn't be lazy let me put the unit's 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 well let's even define it a little bit more it's positive it's not negative it's positive what does that mean for 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 that means it's going to try to deflate okay let's now let's do the transfer Rasik 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 T T P which is a transthoracic pressure is equal to the anti b intrapleural pressure so I'm going to put P IP minus B 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 zero zero millimeters of mercury okay so then if that's the case then transthoracic

pressure is actually just equal to the intrapleural pressure then because this is zero so what does 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 formula musa mercury means that is 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 one 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 we can mention it really quickly and it's just again intra alveolar 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 t RP so trans respiratory pressure is equal to thee p-pull minus D P of the atmospheric pressure okay well what is that equal to that's equal to zero minus zero so will this be it'll be zero

millimeters of mercury and again we're doing all of this at rest this will be zero millimeters of mercury is all arrest we're going to compare this to what it would look like afterwards whenever we're going to do the inspired 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 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 in transthoracic are the more important pressures transthoracic pressure I'm sorry transpulmonary pressure is the intrapulmonary minus to enter plural and we said again you'll take this zero millimeters of mercury which was 760 again we could write like that my name is the intrapleural which could either be 756 or is here right negative four doesn't matter you're still going to get the same number which is going to be positive four millimeters of mercury again what does that mean that means that this is trying to expand ours that you

want what you won here is you want this actual long 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 do you really what are you actually left with you're really only left with intrapleural pressure so if that's the case then you're 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 is 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 and the surface tension of the lungs which is trying to pull the actual visceral pleura away from the product Laurel what is that doing to the volume it's increasing me volume and what would

that do to the pressure in this area it'll 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 engineers I'll see you in part two