Does FVC vary?

I know there was a discussion not long ago about lung fuction tests, and somebody helpfully gave this link:

However, what I am still a little confused about is which numbers are variable and which are not?

I know peak flow goes up and down, but should the others?

My FEV1 has dropped by over 20% and the FVC by 10% on the last set of results from eight months ago. Does this matter, or is this just one of the those things, like peak flows varying day by day?

I do also have very mild bronchiectasis, so I'm inclined to worry about anything that might suggest irreversible progression.

What do others understand? Does FEV1/FVC go up and down in an asthmatic like the peak flow does?



4 Replies

  • FVC can be variable, now I am trying to dig in the back of my memory to think what changes it...

    I think it can be effort related, and may also be affected by your asthma being a bit worse - if you are tight your fvc can go down I think.

    Don't think it suggests bronchiectasis getting worse. But if you are having it done, then ask whoever is doing it for more info.


  • ooo lung function interpretation still blows my brain a bit!! Owl obv knows more than me. But from what i can remember like with PEFR and FEV1, FVC decreases in obstructive airways disease so i assume that if ure more 'obstructed' than previously then the value with decrease. Hope that makes sense! Also as owl says it is effort dependent so it can vary from one day to the next.

  • Thank you very much!!

    The doctors are never worried as my lung function results are generally very good - often over 100%. I put this down to many years of competitive swimming and singing (don't know if this actually does anygood but I like to think so!).

    However, because I've had such good lung function, I would like to hold onto it! If I continued dropping at this rate, and it wasn't reversible, then I'd soon be into trouble, no matter what percentage I started from.

    As long as things are reversible then it doesn't matter - I shall just have to try harder next time!


  • Carrie,

    Keep an eye on MEF ( maximum expiratory flows) at 50% and 25% of vital capacity, -this number gives important info re lung conditions including severe asthma and other lung probs, over some time - and is a sensitive indicator as to what is happening in mid/lower airways. (We asthmatics need all the alveoli we can maintain!)

    Like you I have variable - thank goodness- FEV1/FVC values. And like you have been ’praised’ -not that I needed that info – for many years of long distance running, which apparently is the reason why I don’t need oxygen today! LOL.

    Try to avoid ‘triggers’ and keep up with anti inflammatory meds AS MUCH AS POSSIBLE. Whatever they are. ( meds that is)

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