Asthma is classified as an Obstructive lung disease and primarily affects the airways. It is characterized by chronic inflammation and constriction of the muscles in the airways. These two processes act to narrow the airways and reduce the speed that air can flow in and out of the lung. Asthma does not tend to affect the alveoli or the structure of the lung.

Asthma status is best monitored by FEV1 and PEF.

A typical PFT pattern for Asthma:

Spirometry FVC Normal or reduced
  FEV1 Reduced
  FEV1/FVC Ratio Reduced
  PEF Reduced
Lung Volumes TLC Normal
  RV Normal or elevated
Diffusing Capacity DLCO Normal or elevated
Oximetry SpO2 Normal or reduced

The severity of obstruction is determined by the reduction in FEV1. When the FEV1 or FEV1/FVC ratio are reduced:

FEV1 >= 70% of predicted Mild
FEV1 <70% and >=60% of predicted Moderate
FEV1 <60% and >=50% of predicted Moderately severe
FEV1 <50% and >=35% of predicted Severe
FEV1 <35% of predicted Very severe


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PFT Patient by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

2 thoughts on “Asthma”

  1. I’m curious about this test, I recently had this done.
    I should mention I have had asthma my entire life but have been fine with meds until recently I have been having blood pressure problems in which my doctor decided to put me on a beta blocker, since then my breathing has been terrible.
    I should also add I have had 2 sinus surgeries in 2014 which at first worked great but a recent CT showed 2 of my sinuses clogged again which I had suspected as it’s difficult to breath out my nose yet again. ?
    I don’t struggle at rest only when active, steps are breath taking these days. I have mentioned this to my doctor numerous times and he just sent me to have the PFT done while there the lady doing the test told me this was a bad case of mismanaging my medications as I was on a Ventolin Inhaler and Advair 250/50 since I was young, I am now 41. She stated my results improved greatky after they administered a higher dose of my medication (the inhaler only)
    After the initial testing my reading were 54% after the stronger dose of Ventalin (one puff) my reading went up to 69%.
    I really don’t know what any of these numbers mean or how true they are when you go in with a chest cold and a sinus infection for the testing but due to this my doctor has given me the diagnosis of COPD and told me I’m not that old but have 75 year old lungs now.
    He offered no real explaination just put me on a higher dose of Afvair (500/50) as well as a new medication called Tudorza Pressair 400mcg 2x’s daily.
    He did not x-rays or anything to follow up he didn’t even listen to my lungs not once even though I have complained for about a year since being but on this beta blocker that life is miserable now with breathing during excersise.
    I’m beside myself and I’m not sure what to do or if this disagnosis is just given me being sick and no other testing to confirm or a repeat of the PFT at a later date after I’m over this illness I currently have.
    Does anyone have any insight? I am very scared I have 4 young children and being told I have 75 year old lungs is a scary place to be given the diagnosis he has just handed me.
    If anyone has any advice or help to offer I would greatly appreciate it.
    Thank you in advance for any help!

    1. KJ –

      I suspect that what the technician told you about your results had to do with your FEV1 (the amount of air you can blow out in 1 second). An improvement to 69% from 54% says you have hyperreactive airways (the latest medical slang for asthma). I don’t think it was her place to tell you your medications were being mismanaged however, and that is partly because she is only seeing you once and has no idea how good or bad your lung function was in the past, but also because she’s not a physician. I’ve been performing pulmonary function tests for over 40 years and although I know a lot about lung physiology, the equipment and the tests I am very aware that I don’t know that much about treating patients and in particular I don’t know a lot about the newer medications.

      However, I’ll also say that I don’t agree with you being told your lungs are 75 years old. Estimated Lung Age was created as a tool to help motivate smokers to quit smoking but it is very problematic. The thought was that the lung damage that occurs from smoking mimics premature aging of the lung. The idea is to rework the reference equation for your FEV1 so that you instead of entering your height and age and getting your expected FEV1, you enter your height and FEV1 and get your expected age. The problem with this is that it uses a single (and old) formula for this and that even very small changes in FEV1 look like big changes in age. But also, you’re not a smoker (or at least you didn’t say you were) so using this formula for somebody with asthma or pulmonary fibrosis is a big no-no.

      FYI, beta blockers help control your blood pressure partly by lowering your heart rate, however too high a dose can also prevent your heart from increasing cardiac output (blood flow through your body) enough to deal with the increased oxygen demands of exercise. It’s a balancing act and sometimes it’s more important to lower your blood pressure than anything else.

      Maybe I’m reading too much into what you’ve written but it doesn’t sound like you’re all that happy with your doctor. I don’t know what your options are but sometimes starting fresh with somebody new can bring a fresh outlook to your problems. My wife and I relocated a couple years ago and she had the leave a doctor she loved but the new clinic she’s now going to almost immediately found a number of problems that had been overlooked. At the very least however, you should start seeing a pulmonary physician regularly.

      I’d also strongly recommend that you look for an asthma support group (just google it). You need to talk to other people who’ve had to deal with the same problems as you. You’re not alone.

      Best wishes, Richard

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