Inhaling meth—not that kind: Recounting my Methacholine Challenge Test.
A few years after my asthma diagnosis, and having trouble getting my asthma under control, I wanted to be sure we were treating the right thing—after all, though we were pretty sure I had asthma, there are a few things that can mimic asthma. One of the ways to find out, nearly for certain, if you have asthma—especially if you have good pulmonary function tests—that you do have reactive airways, is to do what is called a methacholine challenge test, a type of bronchoprovocation test. If you read into the word, it essentially means the test tries to provoke, or cause, your airways (bronchi or bronchioles) to react as they would when you are having asthma symptoms.
I did my methacholine challenge, fondly (or not-so) nicknamed the “meth challenge” because I think it’s funny and I’m easily amused, in the pulmonary function lab at the clinic I was attending at the time. My meth challenge was administered by a respiratory therapist (sidebar: he was working in NICU when I was born, and when I spent 10 weeks in said neonatal intensive care unit—what are the chances?).
I had to withhold my medications the day prior to and the day of the test. I started the test with a lower than normal but not terrible FEV1, although my results did not, apparently hit the standard for “start of test”. I am not sure if this was because of my slightly decreased FEV1 (still in the 90s) or my FEF25/75 that was 77% of predicted. Prior to beginning the inhalation of the methacholine, a baseline pulmonary function test (PFT) is done. In some cases, you will be asked to then inhale an amount of saline to see how this affects your lungs—I can’t recall if I was given saline, but I do not think so. If your PFTs before the test are not high enough, you will not be permitted to continue the test.
Then the real fun begins. Simply, I inhaled methacholine from a nebulizer in a set dose, waited, and repeated the PFTs. This happens until a set dose of methacholine has been inhaled, or until your PFTs (FEV1) drop a certain amount—20% from your starting number . Then, you will get a bronchodilator (the respiratory therapist sort of held an inhaler facing me and asked me to open my mouth and I was like “uhhh, can I just use my spacer?” He was like “Oh! You have one with you? Yeah, go ahead!” I felt like coordinating that nonsense would have been difficult.)
For me, I did not really feel as bad during the meth challenge as I thought I would have, however, I did feel worse later in the day. I took Ventolin and asked enough questions about my test that I think I got some hints of an answer. I had to request the printout from my specialist. During the test, my FEV1 dropped 27%—from 94% to 67%. More interesting, especially at the time, was the drop in my FEF25-75%, which is the measure of your small airways in the middle part of your expiration. This measurement can be sort of touchy, but my FEF25-75% dropped from the start of test value of 72%, and fell 45% by the last measurement—I’ll take care of the math, that’s down to 28% predicted. These measurements are very “touchy” so most of the time there is not a lot read into these small airways numbers, as I’ve learned, but given what I know now about my asthma, and that I think there is a lot of small airway involvement because of my prematurity. So this was interesting for me to learn.
The bronchodilator inhalation—the reversal of the meth challenge, if you will—is the most important part of the test. For me, after I think 4 puffs of my inhaler, my numbers were back to where they were before inhaling the methacholine, or just a few points lower.
I felt more short of breath than usual the rest of the day, but for the understanding I gained of my asthma that day, I definitely think it was worthwhile, especially to know we were treating asthma and we were meant to be treating asthma, and clued me in to a few little quirks of my lungs.
Now I’m kind of curious what my exercise challenge results would look like if I were to do such a test. Or a cold air challenge—which is totally a thing, and more controlled than just going outside. Although, I’m not sure I’ll be going out of my way just to inhale cold air… An exercise challenge on the other hand, hmm…
Maybe I AM that curious? ;)
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