DIP Episode 410 - Pulmonary Pathophysiology Series 7

Okay, welcome. My name is Divine. This is episode 410 of the Divine Intervention Podcasts. In today's podcast we're going to be a continue our Permanent Path of Physiology series. This is going to be series 7 and we will be discussing a host of things relating to gas pressures. So let's just go ahead and jump right into it. So the thing is the goal first and foremost with this Permanent Path of Physiology series is to just really get you to understand Permanology on a deep level. In my experience teaching and working with lots of students, I've seen that one of the biggest holes that people have in their knowledge is just Paul. Many people just memorize Paul. They don't really understand it. When they get a basic poem question they get it right. Once they get a question that is anything but basic, they just almost by default get it wrong. So the goal of these podcasts is to prevent you from being in that second category. Permanology is actually one of these things that is relatively easy to understand, especially when you can make integrations and you can see for what it is, especially with a lot of analogies. So let's just continue. So today we're going to look at a lot of gas pressures and we're going to look at like Permanent Restar collation. So the thing is the way blood flows in your lungs is very unique in many respects compared to the systemic circulation. And today I'm actually going to try to bring in a lot of pathologies we go along.

So the thing is your pulmonary vessels are baseline. They are pretty under very low pressures. In fact the systolic blood pressures in your pulmonary vessels are about 25 millimeters of mercury. For your dastolic pressures in your pulmonary system is probably more along the lines of 12. So about 25 over 12. So compared to contrast this with the other that goes at like 120 over 80. That's like way more. The other is literally going at like 5x. The systolic blood pressures of your pulmonary circulation. And the other is going at about from doing my math correctly. About six or seven x. The dastolic blood pressures of your pulmonary circulation. Now you may wonder why is it that we have such high pressures in the other versus such low pressures in the pulmonary system. The thing is your pulmonary system only needs to make blood travel very short distances. Compared this to the rest of the body with the other has to pump blood around the whole body. Right? So if blood has to travel very short distances it doesn't have to be under such high pressures. Since blood in the pulmonary system has to travel very short distances. It doesn't have to be under those kinds of high pressures. And again you want the blood to flow with again not that much speed so that you can have enough time for gas exchange to happen. Although that's a very minor point. The critical thing is the blood in the pulmonary circulation just has to go a shorter distance.

So you don't need as much pressure in that system. I just kind of think of it as like if you're traveling from within like two or three streets in New York. You know you don't need like a high impact vehicle. You can probably just use like a very minor very critical means of transportation and you're fine. But if you're traveling from New York to like California. You're probably certain vehicles you cannot even use for that trip because those vehicles cannot just handle the stress of that trip. Right? You need like a vehicle like bigger heft and things like that. So that's one. Now another thing with your pulmonary vessels. Let's maybe look at the pulmonary arteries. You know pulmonary artery walls they are very thin. Right? Compared to a lot of your systemic vessel walls they're very thin and they're very distensible. They are very very compliant. Right? So they present with almost no resistance to the flow of blood. Now how do these pulmonary vessels respond to hypoxia to a low oxygen tension? Well let's look at the systemic vessels first. The thing is when we're looking at our systemic vessels they actually dilute in a response to a low oxygen tension. Right? So when you have low oxygen tension in your systemic vessels that causes a lot of dilution. Right? Because the body interprets this as like low blood flow and the body sees low oxygen somewhere is like oh there's not enough blood flow to that place. Right?

And usually when you're a hypoxic like that you're going to be making a lot of ADP. ADP is a very prominent viso-dialiter. Right? So you can cause viso-viso-dialation. Right? Those derivatives of ATP when the body sees that while there's less ATP and more of its derivatives like ADP AMP you're going to get viso-dialation. That's for the systemic vessels but the pulmonary vessels are very different. Pornary vessels actually construct in response to low oxygen tension. Right? They construct right? You've probably heard of the strong hypoxic pornary viso-construction. That's where it comes from. They construct in response to low oxygen tension. It makes it possible for you know well-ventilated regions of the long story to receive more blood. The thing is if you really think about it this is actually a very high-yield, very high-yield system. Right? You're investing your efforts where you're going to get the most result. Right? Where you know that wow okay there's not oxygen here. Because literally as a pulmonary vessel your job in life is to pick up oxygen from the lungs so they can send it to the left side of the heart. Where to be disemnitted around the body. So if there's a part of the lung that's not getting oxygen that place is not helping you fulfill your blood's destiny. So you're not going to go there. You're going to go somewhere else. That's very important to know. That's very important to understand.

It's almost like a person studying for the USML Es and spending more time with a resource. Now give them more bank for their buck than diluting their efforts by going after many things that end up not helping them as much as it's possible. I imagine some people listening to this and like wow yeah probably definitely made this mistake. What a number of times in my life right? Well you can turn around and start making the right decisions now. But anyway if you if you really think about it right like there are many applications of this knowledge we just describe with hypoxia right? So like for example when a child is in utero right your lungs are not really working. So there's like a local hypoxia in the lungs right? So there's a lot of pulmonary viso constriction when you're in utero. That pulmonary viso constriction shunts more blood towards the placental system because again just literally the child can get more oxygen from mom that from himself or herself right? Well you see this newborn once the newborn takes their first breath right? It increases the oxygen tension in the lungs it causes a pulmonary viso dilution and things become better right? And the thing is this also explains just many just many many many different things right? They have literally many derivatives of just this one concept right?

Like for example when a person has obstructive sleep apnea or they have COPD or they have cystic fibrosis literally they are pretty under conditions of consistent hypoxia that hypoxia is going to cause a pulmonary viso constriction when you constrict the pulmonary vessels it's going to be really hard for blood to flood of the right side of the heart over time those people will develop pulmonary hypertension that's a high your fact to know that's a high your integration to be able to make or you can even see the MBM Es they love to do this especially on step two and step three where you notice that a VSD becomes louder the longer child lives again it's all based on this principle if you think about it as the child leaves for more and more hours and days they're taking all these deep breaths they're dilating the pulmonary vessels so as you leave more and more from the time of birth if you measure minutes hours later your pulmonary pressures are going down significantly because now there's oxygen around if your pulmonary arterial pressures are going down because of pulmonary viso dilution then the pressures that your right ventricle has to pump a blood against a much lower so it's much easier for blood to flow from the right ventricle so guess what your right ventricular pressures go down as well as those right ventricular pressures go down and we know that your left ventricular pressures are going up more right as you leave more and more then the gradient for flow like literally after a child is born just give minutes give hours left ventricular pressures are going up right ventricular pressures are going down so you essentially see that the pressure spread the pressure difference the pressure gradient is bigger since there's a bigger pressure gradient there's going to be more flow if there's more flow then the murmur of a VSD is going to be louder again this may seem li

ke a benign point but I promise you you will probably encounter this at some point with some USMLE test or some shelf example some sort I'll strongly encourage you to make sure that this stuff I just said if you have to rewind and listen to it again listen to it I promise you there's a lot of physiology a lot of pathophysiology a lot of correct answers victim what I just said right and then if you also look at this I mean we kind of talked about the systemic vessels first if you look at the systemic vessels you can also see that there's an integration you can make with this oxygen business and inter-creature pressures right like we said the systemic vessels when there is less oxygen they dilute so that more blood flow can happen when there is more oxygen they construct so that less blood flow can happen well if a person has increased intra-creature pressures what does your body do or what what can you do to fix that in high ICP well one of the ways you can do that actually the quickest means of lowering intra- credure pressures is by hyperventilation you literally hook the patient of ventilator and the crack up the respiratory rate when you do that you're literally gonna blow off a lot of CO2 your PE your PE CO2 is gonna go down your PE2 is gonna go up it's gonna be high right so you're gonna have a lot of oxygen around all that oxygen that you have around because there's comparatively less CO2 is gonna cause a cerebral viso-construction you have that cerebral viso-construction there's gonna be less blood flow to the brain when there's less blood flow to the brain that's absolutely gonna help with lowering intra-creature pressures right literally if you get an MBME exam question and they're giving you multiple means of lowering a person's intra-creature pressures they put hyperventilation as an answer they put give us a lasolamide as an answer they put give manitone a

s an answer they put give hypertonic saline as an answer the smart first choice is hyperventilation is something that can be done within minutes probably more like seconds actually in the hands of a good pulmonology so I see you attended right something don't very quickly right and it's something that can work very rapidly so just things to kind of keep in mind for exams again this is one of those things you see me mentioned that one of the reasons people find that more recent MBME exams to be hard because they put multiple answers that are correct I have to pick the most correct answer of the bunch right many times this is a lot of knowing your epidemiology that really helps in such circumstances that's something I love to emphasize with my review courses and by the way if you're taking your step two seek your step three or complex level tour three exams anytime soon I was saying especially for the step two step three folks I do have a few courses that may help I know some people want to get their scores in on time for when your applications are downloadable by programs you probably want to try to get to exam done by like September 2nd or September 5th to be safe now I do have a few courses that may help you there when I have an MBME test against strategy scores taking place tomorrow from 4 to 6 30 p.m.

Pacific standard time again there are many people that have attended the scores it has really helped them I've really heard lots of testimonials that wow divine my scores on my practice test my scores on my real exams in pro significantly even my euro cube bank percentages have literally seen people that they've had like 30% 20% euro cube bank a percentage improvement just from taking the course and then I have a bio statistics bootcamp it's gonna be taking place on Thursday so that's next tomorrow from 5 to 9 p.m.

Pacific standard time again a lot of the bio starts these days that pops up on exams is not plug and chop formulas you see many people they just sit down right down 10 formulas and see if I memorize this I'll crush my exams that used to work before that doesn't really work anymore there are very few questions on the USME Ls these days that depend on your ability to regurgitate and plug and choke into formulas most bio statistics and epidemiologic questions are based on a reasoning so if you're looking for a course that'll teach you about a ton of formulas that's not what I'm gonna be doing like 90 probably 95% of the course is invested almost exclusively in just helping you understand if you have the understanding you're gonna be able to crush many of the bio stats questions you you see I've had people attend that course they've done really well actually got a really good feedback from the bio stats course and then I have a 20 hour review course that's gonna be taking place over two days next week the 25th and the 26th of August that's gonna be Thursday and Friday it's gonna be 10 hours each day again it's it's good for you people at any level of your prep so if you're gonna be taking your exam like right after it can be a good way to solidify many things in a two day time span just before you exam if you're studying off your dedicated period it can be a very good way to establish a very solid foundation and even so for some people that say you know what I'm a 30-year-old student but I want to get like a good basis of knowledge for the different disciplines before I start my third year or I mean the middle of my third year and I want to start reviewing ahead for step two or step three it's an excellent course to achieve that because we cover interlural metathesis and a lot of peeds a lot of psych a lot of surgery a lot of neuro a lot of ethics we cover some bio statist

ics and we also discuss the multi-systems persistent disorders communications ethics and things of that nature health care systems and things like that so if you're interested in any of these courses just ship me an email through the website and I'll give you some more information so let's go ahead and continue so the thing is you're pouring vessels right you receive oxygen from your view lie by diffusion you literally receive oxygen from your view lie by diffusion and the thing is diffusion literally depends on three factors three factors and I'll encourage you to remember it with a mnemonic path you know like the name Patrick Pat so the P stands for perc pressure differences the A stands for the area available for diffusion and then the T stands for the thickness of the walls available for diffusion so for P for pressure differences if for area available for diffusion T for thickness of the walls available for diffusion if you increase the pressure difference obviously there's gonna be more there's gonna be more diffusion right because if you're if you're trying to move something from oh 700 millimeters of mercury to 650 versus 700 millimeters of mercury to 100 millimeters of mercury the gradient is bigger in the second case when you have a bigger gradient you're gonna have bigger diffusion also if you increase the area available for diffusion then there's gonna be more diffusion if you notice I'm not introducing the formula first I want to introduce you to understand in first when you have the understanding you can predict the formulas I'm telling you this strive for understanding then your memorization will be more effective there's something I always told people when I used to teach organic chemistry back in the day most of the mechanisms a lot of the synthesis problems in organic chemistry are based on understanding if you have the understanding you don't have t

o memorize the mechanisms you can literally predict what the mechanism should be but again many people just feel feel more comfortable just memorizing things again that's that's not a smart way to leave life or study at all especially for high level exams like the US and the US but that's a different conversation right so if you increase the area available for diffusion is literally like you're just creating more networks for oxygen to move through right if you have more networks available you have more diffusion and then if you look at it from the perspective of thickness since we've been talking about increase increase increase let's look at thickness if you increase thickness well obviously there's gonna be less diffusion happening because it's just harder for oxygen to meet its way through that thicker membrane right so whenever you have an increase in thickness that actually makes diffusion less possible so if you kind of put all these things that just mention together then you can create an equation like well if I just said that as pressure gradient goes up diffusion goes up as as surface area available for diffusion goes up diffusion goes up as thickness available thickness of the area available for diffusion goes up the feasibility goes down then can create an equation you just know that okay well the feasibility of a gas right will be directly related to area directly related to pressure differences that's the pressure gradient and inversely related to the thickness notice you just created that formula but the understanding is there so even if you forget the formula you will always be able to recreate it because the understanding is there right and again it's actually very high your frame exam purposes to know how values in this equation change in different disease right like for example think about it from an infesima perspective when it presents in fesima t

here's all these pretty easy surround right because you smoke the ton of cigarettes your macrophages are coming up to clean up the mess but the macrophages as they clean up the mess they also leave a lot of problems in their week they live a lot of produces those produces will literally chop your lungs or let's say for whatever reason you have problems with folding your phone antitrep cell and then you add on to that smoking right all those things will raise your produces those produces will literally chop your pulmonary pyroincoma when you chop your pulmonary pyroincoma that's not a good thing at all because you have less surface area when you have less surface area then there's gonna be less oxygen diffusion in your lungs and guess what you're gonna become hypoxic as a result of that literally the underlying mechanism behind the hypoxia and infesima is a reduced surface area available for diffusion or you see a person that has pulmonary fibrosis well you have pulmonary fibrosis surprise surprise your fibrolic lung disease you literally have a more stuff in the pyroincoma is almost like all those holes that oxygen normally would use to diffuse across your plug in all those holes with collagen right when you have pulmonary fibrosis you're literally increasing the thickness of the area available for diffusion when that happens when that happens I'll say that again when that happens you're gonna become hypoxic literally the mechanism behind the hypoxia in a person that has intestinal lung disease is an increased thickness of the surface area available for diffusion right literally if you understand those things you understand many of those diseases as well right and really this idea you can actually just think about it in terms of DLCL DLCL is another way to express the feasibility but again you have to memorize these things if you just understand right like your DLCL s

hould be decreased in infesima because again you have less surface area you don't have enough diffusion your DLCL should also be decreased in a person that has intestinal lung disease because again there's just thickness of that membrane over which diffusion is supposed to happen right there's just more thickness there right but whenever you have like more diffusion you can have to be having increased DLCL I mean think about it for presence of polycyphemia there's literally just more blood available to pick up oxygen right so since there are more like empty seats available on hemoglobin because you have polycyphemia then you're gonna be welcoming more and more gas from the outview like more and more gas from the outview like more and more gas from the outview like that's literally going to raise your DLCL that's literally just an example of something that can raise your DLCL right so I think to maybe wrap up today since we've kind of gone along a little bit here let me discuss this whole concept of diffusion and profusion limitation right this is something that really messes people up on exams but again it's very understandable if you think three carefully now one thing I'll say is carbon dioxide is a special gas most of the circumstances that are available that support human life make it possible for carbon dioxide to diffuse carbon dioxide has very few if any problems ever diffusing so is a special case but I think addressing some other gases may be helpful and the other gases are all addressed I'm gonna talk about carbon monoxide gonna talk about oxygen and I'm gonna talk about N2 O dinatrogen oxide sometimes we call that mitros oxide if your dentist you're probably calling laughing gas okay right and then easy would remember that is corn you know like running a corn like a corn man like a C O N the C stands for carbon monoxide the O stands for oxygen the N stands f

or dinatrogen oxide N2 O the reason I'm giving you that order is that it will actually really help you keep certain things straight as we have this conversation of profusion and diffusion limitations so the thing is if you follow that corn pneumonic it tells you the order of lipid solubility it arranges things in increasing lipid solubility so of all the three gases carbon monoxide is the least lipid solubil oxygen is middle of the pack and then N2 O dinatrogen oxide is the most lipid solubil of all these gases again just stick with me as I build this argument for you logically so that you would not struggle with diffusion and profusion limitations so the thing is probably there's all walls and you're of your life they're literally all lipid bilayers they're all lipid bilayers so it should make sense that the most lipid solubil of all these gases right which in this case is din N2 O laughing gas dinatrogen oxide nitros oxide is the most diffusible of all these gases because literally if it's the most lipid solubil then if you're calling through a bunch of lipid bilayers you're gonna have no problems going through right you're gonna have no problems going through right so dinatrogen oxide I'm gonna start calling it nitros oxide right N2 O is the most diffusible of all these gases it is the most diffusible now let me say something so that's one argument the other argument is for the level of any gas to rise in your blood certain things have to happen right the level of any gas in your blood can rise when two things are met when two conditions are met right literally the levels by how much you rise are determined by two things one the gas most diffuse across the walls of your viola and your pulmonary vessels if you live if it doesn't diffuse across the walls of your viola your pulmonary vessels it's never gonna get into the blood in the first place that's one the second thin

g that must also happen is that there must be a lot of blood flow right so there must be diffusion that's the first condition but the second condition is there must be enough blood flow to carry this gas that you have just putting your pulmonary vessels to the rest of the body that's perfusion right so if you want the levels of any gas to rise in your bloodstream you must have diffusion of that gas it must go across that viola membrane the pulmonary vessel membrane but there must also be enough blood flow to carry that gas away as it's coming into the pulmonary vessels right so you must have diffusion they must have perfusion now one right guilt circumstances right on so that's another argument I just made now the next argument I want to make is that only ideal circumstances if everything is working perfectly the partial pressure of a gas in your viola so inside your viola it doesn't go into the pulmonary vessels yet inside your viola if you bring gas into your viola if things are working perfectly like the diffusion membrane everything is working great then over time the partial pressure of that gas should equal what you see in your pulmonary vessels right because that means that oh diffusion has happened so wow I see an oxygen tension of a hundred in some of my my viola and then hmm I look at the pulmonary vessel I'm like hmm okay well the oxygen tension there is also a hundred if those numbers are similar then that means the fusion is working just fine it means the fusion is working great it means the fusion is working great because gases right everything is equally bright in perfectly now let's then take these arguments we have made and formulate them in the context of diffusion let's look at things from a diffusion perspective right so again I said that nitrous oxide is the most lipid soluble of all these gases right so it literally has no issues getting across t

he diffusion barriers that are available it literally has no issues with that literally the only factor controlling how much nitrous oxide gets to the rest of the body is how quickly it is carried away by the blood that is feeding the lungs right because again it's lipid soluble it can cross the lipid bilayer no problem it has a visa right it has permanent residency to come from your viola to your pulmonary vessels it doesn't have any problems there literally the only thing that controls how much nitrous oxide you have in your body is just how quickly blood can feed that area of the lungs bring it in nitrous oxide to take it away to the rest of the body so nitrous oxide you can see is perfusion limited the fusion is not its limitation because it's very lipid soluble it literally has no diffusion limitations it's more profusional limitation because your viola membrane your pulmonary vessel membranes are like yes nitrous oxide comes through because it's lipid soluble right the only limitation it has is how quickly can you get blood there to carry that nitrous oxide away so that you can take a new fresh nitrous oxide so nitrous oxide is perfusion limited perfusion is a limitation to its destiny not diffusion like if we look at things on the other end of the spectrum you know many times when you train to understand things understand the extremes and then the middle ground will make more sense to you let's look at the other end of the spectrum so let's look at carbon monoxide right we literally said that of all these three gases the con gases carbon monoxide is the list diffusible of all three of them it has a lot of trouble getting across the diffusion barrier right it has a lot of trouble has to work really hard right it doesn't have a visa is not certified to go through that barrier right so that diffusion alone is already a limitation to start right so it makes it very

difficult for levels of carbon monoxide to rise in the blood if it will come in normally the blood flow for the long should be more than enough to get it going but no it has just that diffusion limitation so we can see that carbon monoxide is diffusion limited if you was able to come in then boom he moved global I mean he moved global literally by so it would like 244 affinity compared to oxygen so if you want to understand that listen to the clutch he moved global podcasts I think it was like one or two podcasts ago but let's go ahead and continue to confuse things here but literally he just cannot even get into the primary vessels because he has a hard time calling through those membranes so you can see in that case that carbon monoxide is diffusional limited profusion is not its limitation if you were to get into those primary vessels then it can be carried away by him or global being very very well when he has a big time big trouble even getting in there because the diffusion barrier is just not good okay so carbon monoxide is diffusional limited and also have to be like wow define you're seeing the same point over and over again I want to make sure that you truly understand this if you understand this there are so many clinical problems like you people who solve there so many exam problems they be able to solve right and again I should just voice to this cleaner this podcast is not to help you clinically right is to help you more for exams I just want to put that disclaimer okay this podcast should not replace clinical decision making okay so oxygen on the other hand is in the middle of the pack right so on the normal circumstances oxygen has no issue diffusing across the respiratory barrier right it has no it has no issues in general oxygen cannot get some benefits from carbon monoxide but it also gets some benefits from N2 O right dinatrogen oxide right so oxyg

en really on the most circumstances on the normal circumstances let me use that term on the normal circumstances oxygen generally has no issue diffusing across the respiratory barrier right so for the most part it oxygen is largely perfusion limited because it has no problems getting across the aviola and pulmonary vessel membranes it has no issues so diffusion for oxygen is just fine right so on that normal circumstances you can see that oxygen is a perfusion limited gas it can diffuse fine it's just how quickly blood flow to get it out right so oxygen for the most part is a perfusion limited gas but when you get from a normal circumstance I'm going to an abnormal circumstance so like in a disease state like pulmonary fibrosis oxygen starts running into problems getting across the diffusion barrier on that those conditions you can see that oxygen is diffusion limited you can say that oxygen is diffusion limited and once you have a diffusion limitation right then the oxygen tension on the avioli will not fully equilibrate with the oxygen tension in your arteries so ultimately hypoxemia which is a low bacterial oxygen tension would result right literally the divergence in these values that are supposed to equilibrate is what creates your AA gradient what creates your AA gradient is what creates your EE gradient is what creates your EE gradient that's very very very important to understand okay that's very very important to understand very very important to understand okay very very important to understand now one thing I just want to say that I think may also help you here is there's this thing that people struggle with about distance along the pulmonary arteries so let's say the pulmonary artery is one meter long I'm just making this up right just still with me here right and we know that or let's let's use one mile let's use one mile right let's use one mile so let's

say the pulmonary artery is one mile long right if you put a hundred nitrous oxide molecules in their avioli we said that nitrous oxide finds it very easy to literally diffuse across our viola membranes and pulmonary vessel membranes because it's very lipid soluble so those hundred molecules they will have no problems just jumping through like the moment they get to the avioli they have no problems jumping through and getting to the pulmonary artery right literally all that can happen for them very early so you may have only traveled 0.1 miles on that pulmonary artery that one mile stretch of pulmonary artery you may have only traveled 0.1 miles and boom boom boom boom boom everything diffuses just fine no issues no issues right that is one thing you'll find in a profusional limited gas right like nitrous oxide it literally gets across the avioli membrane so well so quickly that was the blood just literally hits the pulmonary arteries it acquires those things very quickly because again diffusion is not a limitation right those things are more profusional limited but if something is diffusional limited let's say you have a hundred molecules of carbon monoxide because the avioli membrane can transmit them very slowly because they are not very lipid soluble you may have to have traveled like 0.9 miles along that one mile stretch of pulmonary artery for that complete diffusion to have happened right that's what tells you that this thing is diffusion limited right this thing is diffusion limited right again like I've said already pulmonary fibrosis in test and long disease introduces diffusion limitations right so you have pulmonary fibrosis you literally blood would have almost got into the end of that one mile stretch of pulmonary artery again I'm just using that one mile numbers for understanding purposes it's not one mile but you must have traveled that one mile stret

ch of road you must have going close to the end you must have traveled like 0.9 miles for all the stuff to have transmithed from the avioli membrane through the pulmonary vessel membrane to the pulmonary artery right so it takes time right so again pulmonary fibrosis introduces diffusion limitations right pulmonary fibrosis introduces so pulmonary fibrosis induces a diffusion limitation and under another you know school of thoughts that many people have issues with this oh like divine you know why is it that exercise makes pulmonary vessels makes why does exercising produce diffusion limitations because I'm going to be like yeah divine like I noticed you know from my studying many resources say that when you exercise you know it takes longer way to exercise let me let me careful my words here when you exercise blood has gone through a big stretch of the pulmonary artery before there's complete equilibration of a gas like divine why does that happen because I just said that oh you know oxygen on the most circumstances is more profusional limited so let's say you have that one mile stretch of pulmonary artery oxygen literally gets in by like 0.2 miles not a problem but when you have exercise when you're exercising you may have gotten to 0.8 miles before all the oxygen has fully gone through like a hundred molecules of oxygen have fully gone through so why is that the reasoning there is that when you exercise blood is going at a higher speed through your pulmonary vessels blood is going at a higher speed through your pulmonary vessels so on the normal circumstances when you're not exercising you know the boss which is blood moving carrying hemoglobin that can take up oxygen the boss is moving slowly so you can catch that boss early but if the boss is moving much faster let's say a boss is moving at 20 miles okay let's start with 20 miles an hour if a boss is moving at 20

miles an hour you know you don't have to run long to catch that boss right just imagine you're standing at a boss stop right a boss is moving at 20 miles an hour you can run with your humans be catching up quickly but if a blood is moving at 80 miles an hour you have to run for longer to catch that boss because that boss is moving so fast right that boss is moving so fast that boss is literally moving so fast so the thing is when like literally this is like real world physiological circumstances it typically takes about 0.75 seconds for blood to traverse your pulmonary vessels right and really like this gas exchange that I've been talking I mean I've been saying a lot of pulmonary pulmonary pulmonary pulmonary pulmonary pulmonary I'm referring to pulmonary capillaries because really gas exchange happens more with your pulmonary capillaries like pulmonary arteries or veins but it's a minute point it's not going to detract from your understanding right so normally when you're not exercising blood traverses your pulmonary capillaries over 0.75 seconds roughly but when you start exercising especially when you're under like very vigorous exercise the transit time goes down from 0.75 seconds to about 0.25 seconds so literally that you're literally cutting the time like by like 67% right so it's just going to take longer since your blood is going so fast before all those hemoglobin molecules become saturated that are coming through pulmonary capillary is going to be later in the course of that pulmonary artery right so that's why when blood is moving at high speed it introduces diffusion limitations right it introduces diffusion limitations right I'll say that again when blood is moving at high speed when blood is moving at high speed it introduces diffusion limitations it introduces diffusion limitations it introduces diffusion limitations okay so I'm going to go ahead and

stop here again I really hope you found the spot cast to be helpful if you really understand these things I'm telling you there are so many things that will just blow idle that I didn't want to talk about that will just blow idle putting your mind for you again I do offer one of one tutoring for all the USML exams step one two three complex one two three I offer review courses and during the podcast I talked about my 20-hour step two step three complex level two and three course I talked about my MB Me testing and strategy scores for step two and step three I talked about my bio stats bootcamp that's for step one all the way to step three and then I also have a new course called the integrated pathophysiology review is intended more for step one and complex level one again just kind of like you saw in this podcast oh let me get you understanding down first that's the goal of that course is to help you really understand stuff and then when you're then memorizing it's way easier it's so so so much easier for you to understand those to memorize those things that you deeply understood right you may notice that wow just from this one concept I've learned I can memorize 10 or 20 different things because the understanding is there right so that integrative pathophysiology review is more for step one or and complex one but if you're taking step two step three complex two complex three and you know that you have a bad foundation from your basic science years this is a course that'll be perfect for you and then I also help with ERAS applications so like personal statements rec letters are supplemental applications more interviews I can have done this for many years with many people that have marched into many disciplines all the way from the very competitive disciplines like dermatology ENT orthopedic surgery neurosurgery everything and then all the way down to the let uh to yo

u know disciplines that are competitive to be honest with you everything is competitive these days but not maybe not germ competitive right so I've worked with many people I've literally even had people that oh went to I've worked with people that oh went to deal schools and now they're a germ resident right so if that's something you're interested in uh just reach up to me through email now give you some more information you can email me through the website and then I have these podcasts on Apple podcasts on Google podcasts and on Spotify at least the most recent 150 if you want everything from episode one just go on the website divineinterventionpodcasts.com if you actually have a Word Press account then you sign up you get an email notification whenever I make a new podcast and then maybe will have also said well divine I you know do you have videos yes I do have videos if you you can find them on the website but you can also find them on my youtube channel divine intervention usmly podcast and videos that's where I post the videos that I make and again like I've been announcing gonna be making some changes to that youtube channel divine intervention usmly podcast and videos you want to see these changes subscribe to the youtube channel when I make those changes you're gonna see them and then finally many of you will have told me that well divine I really love the life lessons that you put at the end of your podcasts so I said to start a new website called divineinterventionlifelessons.com I do actually have a podcast attached to it on Apple podcast it's called the divine intervention life lessons podcast every week I make about two podcasts that are from a biblical perspective addresses a life lesson so if that's something you're interested in feel free to please please check that out there many things we talk about there all the way from you know working hard to d

ealing with opposition to marriage to being a good parent just many many different things on on there so I think that's something you're gonna find to be pretty helpful so again I'll just encourage you if I maybe I should make this my life lesson today I don't know why I just have this deep bread in my heart but please please please whenever you're doing anything in life seek to do that thing from an understanding perspective don't do things on a surface level do things on a deep level when you do things on a deep level you do quality and you'll get quality outcomes you do quality and you will get quality outcomes many people just don't do things on a deep level at all and then you notice that they are massively struggling massively massively massively struggling right when you have understanding first you can teach other people and teach them well when you have understanding you can take exams and take them well because the thing is when people say that mbm exams are tricky many times it's just they don't have the right level of understanding to meet that exam right so we are nice with you even being a good test sticker requires understanding if you have understanding of the way mbm questions are set up then you are more apt to reading through whatever tricks or whatever pitfalls or whatever destructors depletion your path like literally when I teach my mbm testing strategy we discuss the thinking and the reasoning behind the setup of mbm questions when that understanding is there then you stop falling for the traps that the mbm is placing you away so link courage you whatever you're doing in life even marriage I'm telling you this even marriage requires wisdom and understanding there's a certain level of wisdom and understanding that is necessary to get along with your spouse to dwelling peace with your spouse and to make that marriage move forward even in raising k

ids I'm telling you there's a certain level of wisdom and understanding that is necessary for you to raise kids and raise them successfully because we live in a world where there are just so many things that can get kids in the wrong direction you need wisdom you need understanding there's not like drive through parenting right there's more like parenting with understanding when you parent with them because people say oh it's really hard to raise kids well in this day and each yes it's hard but it's not impossible you can raise kids well if you're doing it with wisdom and understanding you can succeed on exams if you deal with wisdom and understanding you see some people they put in a thousand hours and they don't get anything from their studying for you SML exam they still feel and then you see people that have been studying for years I mean literally I've worked with people one on one of one of the more common reasons why we'll reach out to me as well divine I've literally been studying for this comp exam or this USML exam for two years for one year I've no meeting any headway and then you analyze why they're making those mistakes and it's just because they're not working with understanding right you need to work with understanding you may have only one month to study for USML exam but you can study for that one month and get a 260 get a 270 because you're working with understanding I'm telling you never discounts the importance of wisdom on the standing and prudence in making the right moves in life right even investing requires wisdom and understanding being in residency and doing well in residency requires wisdom and understanding taking tests requires wisdom and understanding so I'm encouraging you before you jump into an activity ask yourself what is the wisdom and understanding necessary for this thing learn that thing first the time you spend learning that th

ing will make things way easier for you like for example for me like in pre-arounding and in arounding and in writing notes there's a wisdom and understanding that is necessary you have those you can crank through patients very quickly and accurately so thank you for listening to me today have a wonderful rest of your day I'll see you in episode 411 God bless you bye for now

Pulmonary pressures are very low (Systolic $\approx 25 \text{ mm Hg}$, Diastolic $\approx 12 \text{ mm Hg}$), significantly lower than systemic pressures ($\approx 120/80 \text{ mm Hg}$).

Systemic vessels dilate (vasodilation) in response to low $\text{O}_2$. Pulmonary vessels constrict (vasoconstriction) in response to low $\text{O}_2$ (Hypoxic Pulmonary Vasoconstriction).

P-A-T: Pressure gradient, Area available for diffusion, and Thickness of the membrane.

Oxygen ($\text{O}_2$). Because it diffuses easily across the alveolar membrane (diffusion is fine), its partial pressure in the blood is primarily controlled by how quickly blood flow delivers it to the lungs (perfusion).

Carbon Monoxide ($\text{CO}$). Because it has difficulty crossing the alveolar membrane due to poor diffusion properties, its partial pressure in the blood is primarily controlled by how well it can diffuse across the barrier.

Nitrous Oxide ($\text{N}_2\text{O}$). It is the most lipid-soluble of the three gases, allowing it to pass through lipid bilayers easily.

Pressure gradient (the difference in partial pressure across the membrane).

The thickness of the alveolar-capillary membrane is increased. This impairs diffusion, leading to hypoxemia ($\downarrow \text{PaO}_2$).

Chronic alveolar hypoxia triggers Hypoxic Pulmonary Vasoconstriction (HPV), increasing resistance and pressure in the pulmonary circulation.

When it diffuses easily across the membrane, meaning its blood concentration is primarily controlled by the rate of blood flow delivering it to the lungs.

Hyperventilation, which causes respiratory alkalosis and subsequent cerebral vasoconstriction.

Nitrous Oxide ($\text{N}_2\text{O}$). This high solubility makes it highly diffusible.

Pressure gradient (the difference in partial pressure across the membrane).

The thickness of the alveolar-capillary membrane is increased. This impairs diffusion, leading to hypoxemia ($\downarrow \text{PaO}_2$).

Chronic alveolar hypoxia triggers Hypoxic Pulmonary Vasoconstriction (HPV), increasing resistance and pressure in the pulmonary circulation.

When it diffuses easily across the membrane, meaning its blood concentration is primarily controlled by the rate of blood flow delivering it to the lungs.

Hyperventilation, which causes respiratory alkalosis and subsequent cerebral vasoconstriction.

Nitrous Oxide ($\text{N}_2\text{O}$). This high solubility makes it highly diffusible.