- diagnosing asthma can depend on a particular doctor's practice. i've seen it diagnosed with the history, and if the asthmamedications work for them, then they have asthma. but to be more methodical about it, let's talk about the gold standard tests 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, butit is the best way to tell. we call it the methacholine test. methacholine. now, this substance issomething you inhale, and then we observe what happens. methacholine test. so, if we have our normal airway here. the lumen is nice and big,
and our smooth muscleis just floating around, not constricting too much. now, when we give the 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'sa little bit smaller. it's going to be a littlebit harder to breathe.
if this person has asthma and their lungs arepredisposed to really react, then their lumen might be this big, and the smooth muscle is going crazy constricting this airway, making very little roomfor the air to go through, and you have asthma. so, this is just testinghow your lung responds to something that makes it constrict,
because asthma just describes the tendency of the airway to react this way. so, if the methacholine canget your lungs to do this, in the small airways, then that is a positive test for asthma. so, how exactly do we knowthat the lungs have done this? and we can see thisthrough a group of tests, and this is done withor without methacholine. it's a very standard test to do
when people have all kindsof respiratory issues. we call it the pfts orpulmonary function tests. so, pulmonary refers to the lungs. we're testing the function of the lungs. pulmonary function test. all right. so, what happens is wehave our lucky patient. let's make him orange. we have our lucky patient with hair.
i always draw hair on my people. so, mr. bob here says, ihave trouble breathing. so then, pulmonary function tests. we give him a mouthpiecethat he puts in his mouth, and then when he's breathing in or out a machine records everything that happens, the volume of air, the speed of air. let's call this our pft machine. so, the real thing is alot more sophisticated
than my rendition here. and i've actually done this test. they thought i might havehad asthma when i was a kid, and i had to do this test, andlet me tell you, it is not fun. what they do is, they 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 canand for as long as you can, until you feel like there'snothing left in your lungs,
and you're going to die. and that's what's necessaryto 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 mouthpiececatches all of the air. so, the air actually goes in here. i'm going to erase allthese things out here. so, just remember that themouthpiece catches all this air,
and pulmonary function test depends on the fact that all the air isisolated into our machine. okay, there's some math involved here. so, believe it or not, even though you're breathingout for as long as you can, it can last a long time,depending on your lung capacity. most of the air should comeout in the first second of your breathing out. so, we call this the fev-1.
the one stands for the one second. so, the amount you breatheout in the first second divided by the full vital capacity, which is all the air you everbreathe out until you gave up, that's the full vital capacity. the ratio here, one divided by this, should, in a normal lung, beequal 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'll put a little a here, in fact, in all obstructive diseases where breathing out is a problem, the fev-1 divided bythe full vital capacity will be less than 80. so, actually some people say less than 75,
but you know by thisratio being diminished that something is wrong with this exhale, that less than 80 or 75% of the air came out in the first second. that means the lungsare not elastic enough or for some reason the air's not getting through fast enough when you're putting all thatforce behind it to breathe out. so, this forced vitalcapacity test with the ratio
is one of a group of teststhat's done with this machine. we call this spirometry, and spirometry can be done with the methacholine challengeor without at any time. mathematically, these numbers here really tell us a lot abouthow your lungs are behaving when you're exhaling. so, next let's talkabout the peak flow test. the peak flow actually is notjust used to diagnose asthma.
this is used by people who have asthma, to monitor their disease. peak flow. and this standard iscreated for each person. so, they know for yourlungs what is the 100%. so, knowing your 100%, every time you do the peakflow test and you exhale, the machine can tell at what percentage of your maximum you're at.
so, imagine this personalready has asthma. sometimes you can have a littlebit of reaction going on, and you can't really feelthat out of breath yet. so, this is just like a traffic light. when the machine gives you green, that means your at 80 to 100% of your max. so, you can keep going about 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 personprobably has some symptoms. they can feel short of breath. they can be coughing, maybe a runny nose, or they're sick with something else, and this gives you about50 to 80% of your max. 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 thatyou're back in the green. and, of course, red means stop, right? so, red is below 50% of your max, and 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 somethingabout your asthma right now, and you probably don'teven need the machine, because if you're at below 50%, this person's going to feel pretty crummy. their chest will be tight. it'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 asthmashould have a normal x-ray. so, why do we still do it? because you don't alwaysknow that they have asthma. the x-rays give people achance to look at the lungs, to make sure there'snothing else going on, because symptoms can be similar.
so, this person can have pneumonia, can have an infection in the lungs, with fluid and consolidation. that's why they're havingshortness of breath. or they could have a foreign body, and that's why they feellike they can't breathe. there could be fluid. there could be mucus. they could have a pneumothorax,
where the lung has partially collapsed. so, all these thingscan be seen on an x-ray. so, sometimes when the 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 stresstest 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'resweating and working hard, does that make their asthma, does that make their breathing worse, because that could pointto exercise-related asthma. and lastly, i want totalk about a test called the nitric oxide test.
nitric oxide is a gas. so, it's made of nitrogen and oxygen, and if we wanted to dothe chemical symbol of it, nitrogen is an n, and oxygen is an o, so no is a nitric oxide test. we do this when we thinkthis person has asthma, but we want to see if asthma treatments will be good for him. what the nitric oxide test does,
is it tells us if aninhaled corticosteroid, which is a standard treatment for asthma-- i'm trying to draw an inhaler here, so an inhaler you push a button here, and this mist comes out,that the person with asthma will breathe in, and itwill help them feel better. so, there are steroids in this inhaler. just sometimes we don'tknow if this person would benefit fromsteroids, 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 corticosteroid ismore likely to work on them. so, we don't do nitric oxide as a therapy. nobody's going to be breathingin nitric oxide every day,
but in the short term, now what happens when youbreathe in nitric oxide can help us predict what would happen when they breathe inthe steroid treatment. so, this is diagnostic butalso helping us to treat.