Understanding Pulmonary Function Tests

What's up Ninja Nerds? In this video today we're going to be talking about PFTs, pulmonary function tests. This is going to be part of our clinical medicine section. If it helps you, it makes sense to you, please support us. And you can do that in many ways. One, hitting the like button. Two, commenting down in the comment section. Three, subscribing. And if you really want to support us, please do so by liking, commenting, and subscribing. to you can also support us and yourself by going down the description box below clicking the link to our goes to our website where we have amazing notes illustrations questions on top of that even developing exam prep courses and we have merchandise there all of those things are there please become a member and check out all those things that can be useful for your academic career all right let's start talking about pfts though pfts pulmonary function test it's not just one test it's a bunch of like small tests that come together to help you to discern does this patient have an obstructive versus restrictive lung disease and if they do have one of those which one is it is it asthma is it copd is it a extrinsic type of lung disease for the restrictive categories is an intrinsic lung disease for the restrictive categories and it's really good at sifting that out we'll go through an algorithm I think that'll put all this together. Let's understand it first So the first thing that you usually do is you obtain lung volumes and this can be done via what's called plasmography Now what this gives is this gives you a couple different volumes And I think it's actually kind of important to understand this and patients who have obstructive lung diseases Their lungs are super big so that these big monstrous hyperinflated lungs their lungs are super compliant Which means they want to stretch and unfortunately, they're super stretchy and big and distended because they're hyperinflated They're obstructing their airways which causes the lungs to get dynamic hyperinflation, air trapping. Because of that, they keep a lot of air in their lungs even at the end of expiration. So because of that, their residual volumes are relatively high, and so can also their expiratory reserve volumes. Now there's actually a terminology here, which is the combination of these two, and that's called functional residual capacity. Here, I'll put that as a little kind of note here, that this plus this gives you this. This is really the key thing. In patients who have obstructive lung disease, lung disease, their functional residual capacities are like really, really high. And that's because they can hold a lot of air in their lungs after a full expiratory phase. Now, because they can have a lot of air in their lungs that remains in their lungs, they don't have a lot of volume that they can take a deep breath in above that. So imagine, take a deep breath, hold it, don't expire, and then try to take a deep breath on top of that. That's what these patients are living with. Because of these three things here, it makes it so that the actual amount of deep breath that they take in above their normal tidal volume is tiny so they can take potentially normal to lowish tidal volumes but here's the big thing their ability to take these deep breaths in are usually reduced and that's one of the classic things that you'll see in these patients that hyperinflation leads to reduct reductions and inspiratory volumes okay cool what about restrictive lung diseases and these patients their lungs are super fibrotic they're stiff They don't want to expand. They don't have the ability to stretch. They're not very compliant at all. Their elasticity is increased and they want to be the small size possible. So because of that, they don't keep a lot of air in their lungs even after expiration. So their reserve volumes are low. Their ERV is low, which is the amount of air that you can forcefully exhale beyond a normal tidal volume expiration. So because of that, if you take the combination of these two and you look at the functional residual capacity, it's also reduced, right? So you have a a reduced functional residual capacity. Now you would probably think, oh okay, well if it makes sense of what Zach said, if they have a low functional residual capacity, they got tiny lungs, so they could probably take in deep breaths. No, unfortunately they can't even take in deep breaths either because it's really hard to expand those lungs. It takes a lot of effort. And they unfortunately don't generate good tidal volumes and they don't generate good IRVs. Now with all that being said, one of the things that you'll notice is the combination of all of these components. So the IRV plus the plus the tidal volume, plus the expiratory reserve volume, plus the residual volume, gives you what's called a total lung capacity, the maximum amount of air that these patients can hold in their lungs. In this scenario, it's gargantuous because of their FRC. So they have a very large total lung capacity. In this scenario, they have a tiny little total lung capacity. So their total lung capacity would be really, really small. Now, a lot of this stuff is, all right, Zach, I see a lot of abbreviations, a lot of different things. Is there an easier way to remember this? So in other words, Zach, Zach, if I get a graph that shows up on my exam or on my PFTs and I'm having to read them as a clinician, how do I determine if it's more obstructive versus restrictive? Well, sometimes what they do is they use this thing called flow volume loops. And it kind of takes into consideration all of these things that we just talked about. So here in black is going to be the normal patient, right? And the normal patient from this inspiration to expiration, This whole component here is what we refer to as the forced vital capacity for the normal patient. And then the amount of air that remains in their lungs, right, after a forceful expiration is... called their residual volume. And then from here to here is their total lung capacity. This is all in a normal patient. Now you take an obstructed patient. What's the characteristic here? And these patients their curve or their flow volume loop shifts to the left and when it shifts to the left look at now their force vital capacity so here is the beginning part of inspiration and then expiration now their force vital capacity in comparison to this one here if you compare these two so this one to this one it's reduced and compared to the normal scenario but look at this crap here from here to here is your residual volume it increases significantly. And that, again, helps you to remember that. And then finally, if we were to take the combination of these two, which is your total lung capacity, it's going to be increased in compared to the normal patient. Look, look how much wider that is. So that's one of the big things that will help you. As total lung capacity goes up, residual volume goes up. As a responsibility of the residual volume going up, the ERV will also kind of go up a little bit, and so will the functional residual capacity. So they can't take... taking deep breaths. Now, we go to the other patient with restrictive lungs. So here's the normal. From this point here of the inspiration to this point of expiration is your force vital capacity. This point here from the end of the force vital capacity the amount of air that remains in, is your residual volume. And then again, the collection of these two is your total lung capacity. If we look here at this, what we notice from restrictive lung diseases is that they shift to the right. of the curve. And when they shift to the right of the curve, what does that do? Their force vital capacity, in comparison here to this one, will reduce. Significantly, actually. And then on top of that, their residual volume will go down. And then if you look at these patients total lung capacities, it's so tiny. And that's one of the big things that you'll be able to obtain from these patients when you look at their flow. low volume loops. Obstructed, shifted to the left. Big residual volumes, big total lung capacities. Restrictive, shifts to the right. Small total lung capacities, small residual volumes. That is the big concept to take away. All right. So we perform this test and we get this. It'll help us to say I'm supporting more obstructive versus more restrictive. Let's go to the next test. This is really the hitter. This is the Mac daddy of most of the kind of PFT tests. That's called forced spirometry. What you do is you take You take an apparatus, you take a deep breath in, and you breathe out as forcefully as you possibly can, and it measures that expiration at one second and throughout the entire time that you expire. And it gives you this graphical representation we see here. Now you get two values from this, and then you can form a third. One is you look at what was the amount of air, or volume, that expired on the y-axis at one second. And both of these scenarios, look at that, was the amount of volume expired at one second. This is called the FEV1. FEV1. So that would be the amount of air I can forcefully expire. And this would be an obstructive patient afterwards and a restrictive patient later, right? We're going to look at the comparison here. What do I notice now? Holy stink. And this patient, if I go here and I come over here, their FEV1 drops significantly. So they have difficulty getting air out more particularly within the beginning of expiration. expiration. So their FEV1 is massively, massively reduced. Okay. Here, I don't notice as much. There's a little bit of a drop off in the FEV1, but not as much in comparison to this one. But there is a little drop off in the FEV1. So they do have a teensy bit of a difficult time exhaling in the first one second. Then I look at the forced vital capacities. And the forced vital capacities, and I actually want to form this to be a little bit worse. just so you don't get confused here with the graphical representation. Okay. In this scenario here, what am I noticing? Well, here, this is the end point, the maximal point. The highest point of the curve is what we refer to, and I'm going to say it's like right here, as the force vital capacity. Same thing here, kind of flattens out force vital capacity of the normal patient. All right. The highest point of the graph here for the blue line will tell me what their force vital capacity is. And it's right here. and right here. So look at the actual drop in force vital capacity between these two. So you're getting the point, which one has the worst force vital capacity? The restrictive patient. So they usually have a very significantly low force vital capacity, whereas the patient who has obstructive is not as severe. So with that being said, if you're having a difficult time, remember, obstructive, FEV1 is the problem. Restrictive, FVC is the problem. Then from there, take the ratio. If this number is really, really really low, and this one is just a little bit low. The numerator is super, super tiny. What's going to happen to the FEV1 over FEC ratio? It's going to be low. And we say that low is less than 70%. All right. And that would be suggestive of obstructive lung diseases, COPD, asthma, bronchiectasis, one of those. For this scenario, the numerator is just a little bit tiny, but the denominator is the the problem here. That's really tiny. What happens to the overall number? It's big. You take a number like this, okay number, divided by a really, really small number, you're going to get a really big number. So generally, these are greater than or sometimes equal to 70%. So they can be in normal or above normal ranges for restrictive lung diseases. So, so far, if I take a combination of these two tests, I will have a pretty good idea. If I look at total lung capacity, residual volume, I look at force vital capacity, FEV1 and FEVC, I should be able to get a good idea of whether it's obstructive versus restrictive lung diseases. So if I had a patient who comes in, I get this, it shows shifting to the left, high total lung capacity, high functional residual capacity, high residual volume, and their FEV1 over FEC ratio is less than 70, it suggests obstructive. Whereas they have a tiny total lung capacity, tiny residual volume, FEV1 over FEC suggests it's greater than or equal to 70. to 70%, it suggests more restrictive type of diseases. Then what do I do? Let's come down to the next test. The next test I'm going to do is I'm going to say I have a patient who has an obstructive lung disease. And I want to know, is it COPD or is it asthma? In other words, is it irreversible or reversible? So what I do is I give the patient a bronchodilator. We call this a short acting beta 2 agonist. And what this will do is this will act on those bronchial smooth muscles and relax them. So in this scenario, look, I can't. get very much air out. FEV1 is probably really low on this one. Then I give them a bronchodilator, opens up the airways. I can get more air out in the first one second. So I would expect my FEV1 to improve after we give them a beta 2 agonist. And if the FEV1 does increase, that's great. But what I need to know is, does it increase greater than 12%? If it does not, it's more suggestive of what? Obstructive lung disease is secondary to COPD. It's an irreversible process. I take the asthmatic patient. I do the same exact thing. I give him a short-acting beta-2 agonist. Goes and acts on these bronchial smooth muscles. They super dilate. All right? Now, in this scenario, again, difficult to get air out. Dilate them. Ooh, baby. Air be flowing. The FEV1 should do what? It should go up. I'm expiring. more air. Now, if the FEV1 does increase by greater than 12% or at least equal to 12%, then I'm more suggestive of a airway disease that is reactive and can be reversed. All right, cool. Well, how do I even prove this even more? Well, I know that asthma is both a kind of airway disease that is reversible, but it's also inducible. So in other words, I can make it dilate, but I can make it really, really constrict. So if I give them another drug called methacoline, which is this short-acting bronchoconstrictor, what would I expect to happen? I'd expect the reverse thing to happen. I expect them to go from having a dilated airway to a super constricted airway, and I expect their FEV1 to drop. If their FEV1 does drop, I want to know how much does it drop. If it drops by greater than or equal to 20%, that's suggestive of an inducible airway. And if I have both inducibility, right, and on top of that reversibility, it suggests asthma much more so than a COPD. All right. Once we've done that, that helps us with that scenario. But then let's take it another step. We do another test called DLCO testing, diffusion limitation of carbon monoxide. Give the patient a tiny bit bit of carbon monoxide. It sounds terrible, right? But it's not that bad. It's not dangerous. Give it a little bit, and you look to see how much runs through the airway and how much diffuses across the actual alveoli into the blood. And it'll be dependent upon how much carbon dioxide is detected when they exhale. So, in obstructive lung diseases, what I want to know is, what would actually affect the DLCO with an obstructive lung disease? Well, emphysema is one of those that what it does is, we're going to use this, it actually decreases the... surface area, right? So that's what obstructive lung disease would do, particularly emphysema. It causes alveolar septal destruction, it gives these big, sucky, huge alveolar airways, right? Or big alve, airways. Because of that, the surface area drops. If surface area drops, what does that do to the DLCO? They're directly proportional. It should decrease the DLCO. So that would be one thing that I would be able to see in emphysema that I wouldn't really see in things like asthma. I wouldn't really see this in chronic bronchitis. Well, that's interesting. Okay, so I know that in this one, I'm having difficulty with moving gases. Because of this, decreased surface area. Available for gas exchange. In interstitial lung disease, or restrictive lung diseases for this matter, what I know is if you have a problem where there's fibrosis of the airways or the interstitial spaces, I know that that's going to thicken the respiratory membrane, and that's going to decrease diffusion capacity. I increase the thickness, I increase the denominator, what will that do to the DLCO? It will also decrease the DLCO. So these both will decrease the DLCO. And therefore, I'm going to have a difficult time performing gas exchange or diffusion. across this thick respiratory membrane or this decreased available surface area for exchange. Why this is helpful, if I determine a patient has an obstructive lung disease off of the top two tests, I do a bronchodilator test and they show that they're more suggestive of COPD. And then I want to determine, is it emphysema or is it chronic bronchitis? Low DLCO suggests emphysema rules out chronic bronchitis for the most part, in a perfect world. Restrictive lung diseases, I go through, I determine they have, based upon the top to test restrictive lung disease. We don't really do bronchodilator or bronchoconstrictor tests for them. And then we do the DLCO testing. If it's low, it tells me it's intrinsic lung diseases. If it's normal, it's suggestive of extrinsic lung diseases. And that's super helpful. So now what I wanna do is I wanna take you guys step through step of how to diagnostically approach PFTs. Let's do that now. We check the FEV1 over the FEC. That's the ratio. If it is less than 70%, that means that it's an obstructive lung disease. From there, check the total lung capacity, the residual volume, the functional residual capacity, and all of those that should be increased and their flow volume loop would support that, that it would shift to the left. Again, that's suggestive of obstructive. The next thing is to administer a bronchodilator test because I want to know, is it a patient who has asthma or COPD? If I do that and there is a greater than 12% increase in their FEV1, it tells me that they have a really significant reversibility of their disease. So it suggests asthma. I could then take it another step further and say, okay, it's reversible. Is it inducible? Give them methacholine. If their FEV1 drops to greater than 20%, it definitely is suggestive of asthma. In the other scenario, if it's a less than 12% increase in the FEV1, it suggests more of an irreversible process like COPD. But which one is it? Is it emphysema or chronic bronchitis? Do the DLCO. If the DLCO is going to be normal, it's likely chronic bronchitis. But if it's low in the scenarios of decreasing total surface area, it's emphysema. All right, cool. What if I said the FVV1 over the FVC is greater than 70%? It's normal then. Okay, but it could be suggestive of restrictive or normal. How do I prove it? Check the TLC, the residual volume in FRC. It would be normal in a normal patient, but it would be low. TLC, RV, and functional residual capacity are restrictive, and the flow volume loop will be shifted to the right. That would be suggestive of restrictive. Okay, how do I then go further and say restrictive lung diseases can be extrinsic or intrinsic? Check the DLCO. If I check the DLCO and there is a change in the lungs itself, there's more thickening of the respiratory membrane, it'll have a low DLCO. But if it has no change in that and it's normal DLCO, it's extrinsic. If it's low, it's intrinsic and it's an interstitial lung disease. And that's how we would go about diagnosing obstructive versus restrictive lung disease based upon PFTs. All right, my friends, I hope that made sense. I hope that you guys enjoyed it. And as always, until next time.

What's up Ninja Nerds? In this video today we're going to be talking about PFTs, pulmonary function tests. This is going to be part of our clinical medicine section.

If it helps you, it makes sense to you, please support us. And you can do that in many ways. One, hitting the like button.

Two, commenting down in the comment section. Three, subscribing. And if you really want to support us, please do so by liking, commenting, and subscribing. to you can also support us and yourself by going down the description box below clicking the link to our goes to our website where we have amazing notes illustrations questions on top of that even developing exam prep courses and we have merchandise there all of those things are there please become a member and check out all those things that can be useful for your academic career all right let's start talking about pfts though pfts pulmonary function test it's not just one test it's a bunch of like small tests that come together to help you to discern does this patient have an obstructive versus restrictive lung disease and if they do have one of those which one is it is it asthma is it copd is it a extrinsic type of lung disease for the restrictive categories is an intrinsic lung disease for the restrictive categories and it's really good at sifting that out we'll go through an algorithm I think that'll put all this together. Let's understand it first So the first thing that you usually do is you obtain lung volumes and this can be done via what's called plasmography Now what this gives is this gives you a couple different volumes And I think it's actually kind of important to understand this and patients who have obstructive lung diseases Their lungs are super big so that these big monstrous hyperinflated lungs their lungs are super compliant Which means they want to stretch and unfortunately, they're super stretchy and big and distended because they're hyperinflated They're obstructing their airways which causes the lungs to get dynamic hyperinflation, air trapping.

Because of that, they keep a lot of air in their lungs even at the end of expiration. So because of that, their residual volumes are relatively high, and so can also their expiratory reserve volumes. Now there's actually a terminology here, which is the combination of these two, and that's called functional residual capacity. Here, I'll put that as a little kind of note here, that this plus this gives you this. This is really the key thing.

In patients who have obstructive lung disease, lung disease, their functional residual capacities are like really, really high. And that's because they can hold a lot of air in their lungs after a full expiratory phase. Now, because they can have a lot of air in their lungs that remains in their lungs, they don't have a lot of volume that they can take a deep breath in above that. So imagine, take a deep breath, hold it, don't expire, and then try to take a deep breath on top of that.

That's what these patients are living with. Because of these three things here, it makes it so that the actual amount of deep breath that they take in above their normal tidal volume is tiny so they can take potentially normal to lowish tidal volumes but here's the big thing their ability to take these deep breaths in are usually reduced and that's one of the classic things that you'll see in these patients that hyperinflation leads to reduct reductions and inspiratory volumes okay cool what about restrictive lung diseases and these patients their lungs are super fibrotic they're stiff They don't want to expand. They don't have the ability to stretch. They're not very compliant at all. Their elasticity is increased and they want to be the small size possible.

So because of that, they don't keep a lot of air in their lungs even after expiration. So their reserve volumes are low. Their ERV is low, which is the amount of air that you can forcefully exhale beyond a normal tidal volume expiration.

So because of that, if you take the combination of these two and you look at the functional residual capacity, it's also reduced, right? So you have a a reduced functional residual capacity. Now you would probably think, oh okay, well if it makes sense of what Zach said, if they have a low functional residual capacity, they got tiny lungs, so they could probably take in deep breaths.

No, unfortunately they can't even take in deep breaths either because it's really hard to expand those lungs. It takes a lot of effort. And they unfortunately don't generate good tidal volumes and they don't generate good IRVs.

Now with all that being said, one of the things that you'll notice is the combination of all of these components. So the IRV plus the plus the tidal volume, plus the expiratory reserve volume, plus the residual volume, gives you what's called a total lung capacity, the maximum amount of air that these patients can hold in their lungs. In this scenario, it's gargantuous because of their FRC.

So they have a very large total lung capacity. In this scenario, they have a tiny little total lung capacity. So their total lung capacity would be really, really small.

Now, a lot of this stuff is, all right, Zach, I see a lot of abbreviations, a lot of different things. Is there an easier way to remember this? So in other words, Zach, Zach, if I get a graph that shows up on my exam or on my PFTs and I'm having to read them as a clinician, how do I determine if it's more obstructive versus restrictive?

Well, sometimes what they do is they use this thing called flow volume loops. And it kind of takes into consideration all of these things that we just talked about. So here in black is going to be the normal patient, right?

And the normal patient from this inspiration to expiration, This whole component here is what we refer to as the forced vital capacity for the normal patient. And then the amount of air that remains in their lungs, right, after a forceful expiration is... called their residual volume.

And then from here to here is their total lung capacity. This is all in a normal patient. Now you take an obstructed patient.

What's the characteristic here? And these patients their curve or their flow volume loop shifts to the left and when it shifts to the left look at now their force vital capacity so here is the beginning part of inspiration and then expiration now their force vital capacity in comparison to this one here if you compare these two so this one to this one it's reduced and compared to the normal scenario but look at this crap here from here to here is your residual volume it increases significantly. And that, again, helps you to remember that.

And then finally, if we were to take the combination of these two, which is your total lung capacity, it's going to be increased in compared to the normal patient. Look, look how much wider that is. So that's one of the big things that will help you. As total lung capacity goes up, residual volume goes up. As a responsibility of the residual volume going up, the ERV will also kind of go up a little bit, and so will the functional residual capacity.

So they can't take... taking deep breaths. Now, we go to the other patient with restrictive lungs.

So here's the normal. From this point here of the inspiration to this point of expiration is your force vital capacity. This point here from the end of the force vital capacity the amount of air that remains in, is your residual volume.

And then again, the collection of these two is your total lung capacity. If we look here at this, what we notice from restrictive lung diseases is that they shift to the right. of the curve. And when they shift to the right of the curve, what does that do?

Their force vital capacity, in comparison here to this one, will reduce. Significantly, actually. And then on top of that, their residual volume will go down. And then if you look at these patients total lung capacities, it's so tiny.

And that's one of the big things that you'll be able to obtain from these patients when you look at their flow. low volume loops. Obstructed, shifted to the left. Big residual volumes, big total lung capacities. Restrictive, shifts to the right.

Small total lung capacities, small residual volumes. That is the big concept to take away. All right.

So we perform this test and we get this. It'll help us to say I'm supporting more obstructive versus more restrictive. Let's go to the next test. This is really the hitter. This is the Mac daddy of most of the kind of PFT tests.

That's called forced spirometry. What you do is you take You take an apparatus, you take a deep breath in, and you breathe out as forcefully as you possibly can, and it measures that expiration at one second and throughout the entire time that you expire. And it gives you this graphical representation we see here. Now you get two values from this, and then you can form a third. One is you look at what was the amount of air, or volume, that expired on the y-axis at one second.

And both of these scenarios, look at that, was the amount of volume expired at one second. This is called the FEV1. FEV1. So that would be the amount of air I can forcefully expire.

And this would be an obstructive patient afterwards and a restrictive patient later, right? We're going to look at the comparison here. What do I notice now? Holy stink. And this patient, if I go here and I come over here, their FEV1 drops significantly.

So they have difficulty getting air out more particularly within the beginning of expiration. expiration. So their FEV1 is massively, massively reduced.

Okay. Here, I don't notice as much. There's a little bit of a drop off in the FEV1, but not as much in comparison to this one. But there is a little drop off in the FEV1. So they do have a teensy bit of a difficult time exhaling in the first one second.

Then I look at the forced vital capacities. And the forced vital capacities, and I actually want to form this to be a little bit worse. just so you don't get confused here with the graphical representation. Okay.

In this scenario here, what am I noticing? Well, here, this is the end point, the maximal point. The highest point of the curve is what we refer to, and I'm going to say it's like right here, as the force vital capacity.

Same thing here, kind of flattens out force vital capacity of the normal patient. All right. The highest point of the graph here for the blue line will tell me what their force vital capacity is.

And it's right here. and right here. So look at the actual drop in force vital capacity between these two. So you're getting the point, which one has the worst force vital capacity?

The restrictive patient. So they usually have a very significantly low force vital capacity, whereas the patient who has obstructive is not as severe. So with that being said, if you're having a difficult time, remember, obstructive, FEV1 is the problem.

Restrictive, FVC is the problem. Then from there, take the ratio. If this number is really, really really low, and this one is just a little bit low. The numerator is super, super tiny. What's going to happen to the FEV1 over FEC ratio?

It's going to be low. And we say that low is less than 70%. All right.

And that would be suggestive of obstructive lung diseases, COPD, asthma, bronchiectasis, one of those. For this scenario, the numerator is just a little bit tiny, but the denominator is the the problem here. That's really tiny. What happens to the overall number?

It's big. You take a number like this, okay number, divided by a really, really small number, you're going to get a really big number. So generally, these are greater than or sometimes equal to 70%. So they can be in normal or above normal ranges for restrictive lung diseases.

So, so far, if I take a combination of these two tests, I will have a pretty good idea. If I look at total lung capacity, residual volume, I look at force vital capacity, FEV1 and FEVC, I should be able to get a good idea of whether it's obstructive versus restrictive lung diseases. So if I had a patient who comes in, I get this, it shows shifting to the left, high total lung capacity, high functional residual capacity, high residual volume, and their FEV1 over FEC ratio is less than 70, it suggests obstructive.

Whereas they have a tiny total lung capacity, tiny residual volume, FEV1 over FEC suggests it's greater than or equal to 70. to 70%, it suggests more restrictive type of diseases. Then what do I do? Let's come down to the next test. The next test I'm going to do is I'm going to say I have a patient who has an obstructive lung disease.

And I want to know, is it COPD or is it asthma? In other words, is it irreversible or reversible? So what I do is I give the patient a bronchodilator.

We call this a short acting beta 2 agonist. And what this will do is this will act on those bronchial smooth muscles and relax them. So in this scenario, look, I can't. get very much air out.

FEV1 is probably really low on this one. Then I give them a bronchodilator, opens up the airways. I can get more air out in the first one second.

So I would expect my FEV1 to improve after we give them a beta 2 agonist. And if the FEV1 does increase, that's great. But what I need to know is, does it increase greater than 12%?

If it does not, it's more suggestive of what? Obstructive lung disease is secondary to COPD. It's an irreversible process.

I take the asthmatic patient. I do the same exact thing. I give him a short-acting beta-2 agonist.

Goes and acts on these bronchial smooth muscles. They super dilate. All right?

Now, in this scenario, again, difficult to get air out. Dilate them. Ooh, baby.

Air be flowing. The FEV1 should do what? It should go up.

I'm expiring. more air. Now, if the FEV1 does increase by greater than 12% or at least equal to 12%, then I'm more suggestive of a airway disease that is reactive and can be reversed. All right, cool. Well, how do I even prove this even more?

Well, I know that asthma is both a kind of airway disease that is reversible, but it's also inducible. So in other words, I can make it dilate, but I can make it really, really constrict. So if I give them another drug called methacoline, which is this short-acting bronchoconstrictor, what would I expect to happen?

I'd expect the reverse thing to happen. I expect them to go from having a dilated airway to a super constricted airway, and I expect their FEV1 to drop. If their FEV1 does drop, I want to know how much does it drop.

If it drops by greater than or equal to 20%, that's suggestive of an inducible airway. And if I have both inducibility, right, and on top of that reversibility, it suggests asthma much more so than a COPD. All right.

Once we've done that, that helps us with that scenario. But then let's take it another step. We do another test called DLCO testing, diffusion limitation of carbon monoxide.

Give the patient a tiny bit bit of carbon monoxide. It sounds terrible, right? But it's not that bad.

It's not dangerous. Give it a little bit, and you look to see how much runs through the airway and how much diffuses across the actual alveoli into the blood. And it'll be dependent upon how much carbon dioxide is detected when they exhale.

So, in obstructive lung diseases, what I want to know is, what would actually affect the DLCO with an obstructive lung disease? Well, emphysema is one of those that what it does is, we're going to use this, it actually decreases the... surface area, right?

So that's what obstructive lung disease would do, particularly emphysema. It causes alveolar septal destruction, it gives these big, sucky, huge alveolar airways, right? Or big alve, airways.

Because of that, the surface area drops. If surface area drops, what does that do to the DLCO? They're directly proportional.

It should decrease the DLCO. So that would be one thing that I would be able to see in emphysema that I wouldn't really see in things like asthma. I wouldn't really see this in chronic bronchitis. Well, that's interesting.

Okay, so I know that in this one, I'm having difficulty with moving gases. Because of this, decreased surface area. Available for gas exchange.

In interstitial lung disease, or restrictive lung diseases for this matter, what I know is if you have a problem where there's fibrosis of the airways or the interstitial spaces, I know that that's going to thicken the respiratory membrane, and that's going to decrease diffusion capacity. I increase the thickness, I increase the denominator, what will that do to the DLCO? It will also decrease the DLCO. So these both will decrease the DLCO.

And therefore, I'm going to have a difficult time performing gas exchange or diffusion. across this thick respiratory membrane or this decreased available surface area for exchange. Why this is helpful, if I determine a patient has an obstructive lung disease off of the top two tests, I do a bronchodilator test and they show that they're more suggestive of COPD.

And then I want to determine, is it emphysema or is it chronic bronchitis? Low DLCO suggests emphysema rules out chronic bronchitis for the most part, in a perfect world. Restrictive lung diseases, I go through, I determine they have, based upon the top to test restrictive lung disease.

We don't really do bronchodilator or bronchoconstrictor tests for them. And then we do the DLCO testing. If it's low, it tells me it's intrinsic lung diseases.

If it's normal, it's suggestive of extrinsic lung diseases. And that's super helpful. So now what I wanna do is I wanna take you guys step through step of how to diagnostically approach PFTs. Let's do that now.

We check the FEV1 over the FEC. That's the ratio. If it is less than 70%, that means that it's an obstructive lung disease.

From there, check the total lung capacity, the residual volume, the functional residual capacity, and all of those that should be increased and their flow volume loop would support that, that it would shift to the left. Again, that's suggestive of obstructive. The next thing is to administer a bronchodilator test because I want to know, is it a patient who has asthma or COPD?

If I do that and there is a greater than 12% increase in their FEV1, it tells me that they have a really significant reversibility of their disease. So it suggests asthma. I could then take it another step further and say, okay, it's reversible.

Is it inducible? Give them methacholine. If their FEV1 drops to greater than 20%, it definitely is suggestive of asthma.

In the other scenario, if it's a less than 12% increase in the FEV1, it suggests more of an irreversible process like COPD. But which one is it? Is it emphysema or chronic bronchitis? Do the DLCO.

If the DLCO is going to be normal, it's likely chronic bronchitis. But if it's low in the scenarios of decreasing total surface area, it's emphysema. All right, cool. What if I said the FVV1 over the FVC is greater than 70%?

It's normal then. Okay, but it could be suggestive of restrictive or normal. How do I prove it?

Check the TLC, the residual volume in FRC. It would be normal in a normal patient, but it would be low. TLC, RV, and functional residual capacity are restrictive, and the flow volume loop will be shifted to the right.

That would be suggestive of restrictive. Okay, how do I then go further and say restrictive lung diseases can be extrinsic or intrinsic? Check the DLCO.

If I check the DLCO and there is a change in the lungs itself, there's more thickening of the respiratory membrane, it'll have a low DLCO. But if it has no change in that and it's normal DLCO, it's extrinsic. If it's low, it's intrinsic and it's an interstitial lung disease. And that's how we would go about diagnosing obstructive versus restrictive lung disease based upon PFTs. All right, my friends, I hope that made sense.

I hope that you guys enjoyed it. And as always, until next time.

Transcript for:Understanding Pulmonary Function Tests

Transcript for:
Understanding Pulmonary Function Tests