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Emphysema diagnosis

How do we know a patient has emphysema? Learn how the lungs in chest x-rays look hyperinflated, how spirometry can reveal decreased lung function, and what all those blood tests mean. Created by Amy Fan.

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Video transcript

Voiceover: So if somebody is short of breath and we want to find out could they have emphysema the first thing we might get is a chest x-ray. And let's just look at what a normal chest x-ray might look like. Here you see the shape of the lungs like that and this muscle down here is the diaphragm. It helps us breathe by moving down. In a person with emphysema their x-ray, their picture is going to look more like this. Look at how hyper-inflated these lungs are. They look like puffed out bags. Right. So here let's write hyper-inflated and that's one of the first signs of emphysema or really obstructive disease because all the air is stuck back here. Because these airways have collapses and are no longer elastic so the air stuck back here makes the lung take on this kind of shape. And look at how it's pressing down on the diaphragm. So it's no longer this nice curve. Now it's kind of flat and this makes it harder to breathe because they have less room to go down. The chest cavity is so full and round it's hard for them to make it a little bigger to take more of a breath so look here in their neck. Do you see how the angle here is different from a normal person's neck? That's because they're using extra muscles to help themselves breathe. Extra muscles to further expand that chest to breathe in and I'll hear them they'll be using their ab muscles to try to force some of that air out because the natural recoil of the lungs is gone. So this is our x-ray. It's a good entry point into working something up because it's cheap, it's easy, and all the person has to do is just stand there. Then next this person might be doing some lung function tests and the important one for this one would be forced expiratory test. And here's how it works. So you have a person- I like to give my stick figures a little bit of hair. I think it makes them look a little better. So we have Mr. Bob here. He says, "I can't breathe, "it's hard for me to breathe out." So we give him a mouthpiece to put in his mouth. It's connected to this tube which is then connected to a machine in a nutshell. And we have Mr. Bob take the biggest breath he can possibly take fill up that chest all the way, hold it for a second and then suddenly and forcefully blow it out as fast and as much as he could. I've actually done this test when they thought I might have had asthma. It turns out I didn't, but this test was miserable because they're trying to get you to get all the air out in here so even when you think you have no more left they tell you to keep going, keep going, it just feels like you're going to die, it's terrible, but it's important for them to do that because we're looking for 2 values. Number 1 we want the full vital capacity. What that means is just all the air that he could possibly breathe out. From the top of the breath to when he can't get anymore out that's the FVC. And then we also want the FEV1 which stands for forced expiratory volume 1 and that's because believe it or not even though you were struggling that entire time to get more air out most of the air came out in the first second. This is like so we have candles here like on a cake. When you're blowing out a candle it goes out in the first second. Right. And if it doesn't go out and you just keep blowing without taking a new breath in nothing is going to happen. So in the normal lung about 80% of the air comes out in the first second so FEV1/FVC should be around 80%, but in emphysema, actually in all obstructive diseases this ratio changes. So first the full vital capacity definitely goes down. In obstructive disease you can get less air out of the lungs so that absolute difference between the top of the breath and the bottom it really decreases, but more importantly the FEV1 here goes down much more. That's because that first second of getting most of the air out really relies on the recoil of the lungs and since that's gone the FEV1 here takes a much bigger hit. You know, let's just put some numbers to this whole thing so that we can see it better. Let's say that ... what was his name Bob, Mr. Bob let's say his full vital capacity was 5 litres so he usually should be able to get 4 of it out in a normal functioning lung, but here because he has emphysema let's say his full vital capacity goes down to 4, but this FEV1 is going to go down even more. It goes from 4 to let's say 2. 2 over 4 that's 50% so we want it from 80% to 50%. So do you see how even though both went down this ratio goes down even further and that's diagnostic for obstructive disease so in emphysema the ratio between FEV1 and FVC is going to be less than about 75 to 80%. Actually how much it goes down can tell us how severe Mr. Bob's disease is. Now emphysema is usually related to smoking or working in an environment with a lot of irritants, but if Mr. Bob here doesn't smoke and doesn't work in that kind of an environment and we want to know why does he have emphysema a possible blood test we could do is measure his Alpha-1 Antitrypsin level because the other reason somebody would have emphysema without smoking or being exposed to irritants is to have Alpha-1 Antitrypsin deficiency. All right, really quickly, it would have elastin giving the elastic quality of the lung being destroyed in emphysema because it's usually cleaved by- let's change the color here- elastase ... I'll have to use red because it's like the culprit in this disease that's going crazy eating up all the elastin. And usually this elastase is kept under check by Alpha-1 Antitrypsin this compound made in the liver that stops the elastase. So Alpha-1 Antitrypsin usually allows there to be more elastin in this relationship. Some people can have a deficiency of Alpha-1 Antitrypsin and that's how they get emphysema so if we really want to find out why and we can't explain otherwise we can look for the Alpha-1 Antitrypsin level in Mr. Bob over here. Now in terms of other blood tests there is something we can do called a blood gas. I'm going to put it in parentheses here because it's not going to be the most routinely done thing because first of all it's more expensive than just a regular blood test and it's painful. You're getting blood from the artery instead of the vein which is more sensitive so we're only going to do this is somebody is in the hospital for a bad case of exacerbated emphysema, but blood gas will allow us to find out exactly how much oxygen and carbon dioxide is in the blood. But usually if this person is still doing okay and we don't need to get the blood gas right away we could get what's called a complete blood count. This is from the vein so it's pretty routine. It's not as painful and here we don't get to directly see how much oxygen and carbon dioxide is there, but there is a compound we can test for it's called the bicarb, bicarbonate and this basically would increase if the body is having too much C02 to balance how acidic it is and in emphysema there is usually increased C02 because it's not getting breathed out. So this is easier to do than a blood gas, but still we usually don't routinely do it unless this person is in the hospital not doing well. These tests can tell us more of a snapshot of how this person is breathing and doing at the moment, but for our diagnostic purposes the x-ray, the pulmonary function tests and even the Alpha-1 antitrypsin will be more valuable.