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Video transcript

diagnosing asthma can depend on a particular doctor's practice I've seen it diagnosed with the history and if the asthma medications work for them then they have asthma but should be more methodical about it let's talk about the gold standard test that can be done to say yes this person has asthma so the first gold standard test I actually find kind of cruel and unusual to do this to people but it is the best way to tell we call it the methacholine test meta choline now the substance is something you inhale and then we observe what happens at the choline test so if we have our normal airway here the blumen is nice and big and our smooth muscle is just floating around not constricting too much then we'll give them methacholine everybody's smooth muscles will contract everybody's airway will get smaller so for a person without asthma after the methacholine they might look like this you can tell the lumen is a little bit smaller it's going to be a little bit harder to breathe if this person has asthma and their lungs are predisposed to really react then their lumen might be this big if the smooth muscle is going crazy constricting this airway making very little room for the air to go through and you have asthma so this just testing how your lung responds to something that makes it constrict because as much as describes the tendency of the airway to react this way so if the methacholine can get your lungs to do this in the small Airways then that is a positive test for asthma so how exactly do we know that the lungs have done this and we can see this through a group of tests and this is done with or without methacholine is a very standard test to do when people have all kinds of respiratory issues we call it the PFT s or pulmonary function test so pulmonary refers to the lungs we're testing the function of the lungs pulmonary function test all right so what happens is we have our lucky patient let's make an orange with our lucky patient with hair I always draw hair my people so mr. Bob here says I have trouble breathing so the pulmonary function test we give him a mouthpiece that he puts in his mouth and then when he's breathing in or out a machine record everything that happens the volume of air the speed of air let's call this our PFT machine the real thing is a lot more sophisticated than my rendition here and I've actually done this test they thought I might have had asthma when I was a kid and I had to do this as and let me tell you it is not fun what they do is to tell you to take a gigantic breath in as much as you can hold and then when they tell you to blow out as hard as you can in a store as long as you can do you feel like there's nothing left in your lungs and you're going to die and that's what's necessary to do this function test now my drawing here is very misleading so I drew this like that to show you that the breath is rushing out very fast but the fact is this mouthpiece catches all of the air so the air actually goes in here I'm going to erase all these things out here you just remember that the mouthpiece catches all this air a pulmonary function test depends on the fact that all the air is isolated into our machine okay there's some math involved here so believed not even though you're breathing out for as long as you can it can last a long time depending on your lung capacity most of the air should come out in the first second of your breathing out so we call this the fev1 the one stands for the one second so the amount that you breathe out in the first second divided by the full vital capacity which is all the air you ever breathe out until you gave up that's the full vital capacity the ratio here one divided by this should in a normal lung be equal to or greater than 80% so more than 80% of the air that you eventually can ever breathe out should come out in the first second this tells us you have a healthy lung without obstructive disease but in asthma I put a little a here in fact in all obstructive diseases where breathing out is a problem the fev1 / the full vital capacity will be less than 80 so actually some people say it less than 75 but you know by this ratio of being diminished that something is wrong with this exhale that less than 80 80 or 75 percent of the air came out in the first second that means the lungs are not elastic enough or for some reason the air is not getting through fast enough when you're putting all that force behind it to breathe out so this forced vital capacity test with the ratio is one of a group of tests that's done with this machine we call this spear Rama tree and spirometry can be done with a methacholine challenge or without at any time but mathematically these numbers here really tells us a lot about how your lungs are behaving when you're exhaling so next let's talk about the peak flow test the big flow actually is not just used to diagnose asthma this is used by people who have asthma to monitor their disease peak flow and this standard is created for each person so they know for your lungs what is the 100% so knowing your 100% every time you do the peak flow test and you exhale the Machine can tell at what percentage of your maximum you're at so imagine this person already has asthma sometimes you can have a little bit of reaction going on and you can't really feel the out of breath yet so this is just like a traffic light when the Machine gives you green that means you're at 80 to 100% of your max so you keep going back to your day you don't need any medication you're doing fine and then the next one of course like our traffic light is yellow so yellow means you have to be careful at this point the person probably has some symptoms if you're short of breath it can be coughing may be runny nose or they're sick with something else and this gives you about 50 to 80 percent of your max so you should probably take some medication to open up the Airways a little bit try to get back into the green so take medication wait 10 15 minutes take it again and see try to make sure that you're back in the green and of course red means stop right so red is below 50% of your max if you're at below 50% this person should go to the hospital they need some more aggressive medication it's basically an alarm signal that you should do something about your asthma right now and you probably don't even need the machine because if you're at below 50% this person is going to feel pretty crummy their chest will be tight they'll be hard to breathe so gotta go do something about it now there are other tests that might be less specific to our cause but they're still used so sometimes people will get an x-ray and people with asthma should have a normal x-ray so why do we still do it because you don't always know that they have asthma but x-rays give people a chance to look at the lungs to make sure there's nothing else going on because symptoms can be similar so this person can have pneumonia you can have an infection in the lungs with fluid and consolidation that's why they're having shortness of breath or they could have a foreign body and that's why they feel like they can't breathe there could be fluid you could be mucus they could have a pneumothorax where the lung has partially collapsed so all these things can be seen in an x-ray so sometimes when a person comes in with shortness of breath we do an x-ray to rule out other things that perhaps can be treated differently sometimes people get a stress test similar to a cardiac stress test testing your heart this one tests your lungs because stress tests some people have stress or exercise related asthma so this person walks on a treadmill and we see when they're sweating and working hard does that make their asthma does that make their breathing worse because that could point to exercise related asthma and lastly I want to talk about a test called the nitric oxide test nitric oxide is a gas so it's made of nitrogen and oxygen and if we want to do the chemical symbol of it nitrogen is an N and oxygen is impos so n o is a nitric oxide test we do this when we think this person has asthma but we want to see if asthma treatments good for him well the nitric oxide test does is it tells us if an inhaled corticosteroid which is a standard treatment for asthma I'm trying to draw inhaler here so the hailer you push a button here and this mist comes out the person with asthma will breathe in it'll help them feel better so there are steroids in this inhaler so top sometimes we don't know if this person would benefit from steroids or if they would how much to give and that's where nitric oxide can tell us by breathing in nitric oxide which is something that dilates dilates the airway relaxing the smooth muscles then if the nitric oxide works then the critical steroid is more likely to work on that so we don't do nitric oxide as a therapy nobody's going to be breathing your nitric oxide every day but in a short-term now what happens when they breathe in nitric oxide can help us predict what would happen when they breathe in the steroid treatment so this is diagnostic but also helping us to treat