By Adem Lewis / in , , , /

– 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 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, but
it is the best way to tell. We call it the methacholine test. Methacholine. Now, this substance is
something 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 muscle
is 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’s
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, and 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 is just testing
how 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 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. It’s a very standard test to do when people have all kinds
of respiratory issues. We call it the PFTs or
pulmonary 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 we
have 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, I
have trouble breathing. So then, pulmonary function tests. We give him a mouthpiece
that 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 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 test, and
let 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 can
and for as long as you can, until 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. So, just remember that the
mouthpiece catches all this air, and pulmonary function test depends on the fact that all the air is
isolated into our machine. Okay, there’s some math involved here. So, believe it or 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 FEV-1. The one stands for the one second. So, the amount 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’ll put a little A here, in fact, in all obstructive diseases where breathing out is a problem, the FEV-1 divided by
the full vital capacity will be less than 80. So, actually some people say less than 75, but you know by this
ratio 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 lungs
are not elastic enough or for some reason the air’s 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 spirometry, and spirometry can be done with the methacholine challenge
or without at any time. Mathematically, these numbers here really tell us a lot about
how your lungs are behaving when you’re exhaling. So, next let’s talk
about the peak flow test. The peak 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
that 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 person
probably 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 about
50 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 that
you’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 something
about your asthma right now, and you probably don’t
even 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 asthma
should have a normal x-ray. So, why do we still do it? Because you don’t always
know that they have asthma. The 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, 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. There could be mucus. They could have a pneumothorax, where the lung has partially collapsed. So, all these things
can 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 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 wanted to do
the 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 think
this 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 an
inhaled 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 it
will help them feel better. So, there are steroids in this inhaler. Just 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 corticosteroid is
more likely to work on them. So, we don’t do nitric oxide as a therapy. Nobody’s going to be breathing
in nitric oxide every day, but in the short term, now what happens when you
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.

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