Confused by peak flow readings

Which I really shouldn't be, goodness knows I've had a peak flow metre for long enough. But I've learned one or two things from this forum that I wasn't aware of before, so I'm wondering if you wonderful people out there can help me out.

As some of you will be aware, I went down with a viral infection late on Christmas Eve. Not unexpectedly my peak flow readings began to dip, even though my chest didn't feel too bad. OK, I was coughing, but it didn't feel like an asthma cough (I will usually get an 'itchy' feeling in my lungs when it is). By the time my local surgery re-opened on 29th December I was coughing up brown phlegm and my peak flow had begun to dip even further. Oddly, my chest still didn't feel particularly tight (I hadn't needed to take ventolin, for example). I was on 500 mcg of flixotide morning and evening, but that is normal for this time of year. I rang the local surgery and they fitted me in to see a doctor within a couple of hours. Not my usual doctor, in fact the one I saw is new to the practice and new to me, but she did all the right things. Checked peak flow, checked oxygen sats, discussed what had been going on, checked temperature, blood pressure, pulse and listened to my chest, which she pronounced clear (which was exactly what I had expected). However, she obviously wasn't going to take any chances. She discussed with me whether I should go on antibiotics or oral steroids, and agreed with me that given I wasn't requiring ventolin, oral steroids probably weren't necessary. So I went on a seven day course of antibiotics. Job done.

Seven days later when the course was finished, my peak flow was improving, the cough was going, still sniffly but no more temperatures (hadn't been for five days) - things were looking up. Two days ago my peak flow finally got back to more normal levels - great! Then yesterday I decided to finish a job I had started before Christmas - clearing out a load of old stuff from upstairs. Anticipating problems with dust, I wore a mask. Four hours after I'd finished the job I started coughing. Checked my peak flow - no problems there, everything looking good. This morning the peak flow was still good (reading 420), but I'm still coughing and I have that annoying itchy feeling in my windpipes and lungs which tells me my asthma is playing up.

So why is it that my peak flow went down when I had a virally induced cough but my chest really didn't feel too bad, but is absolutely fine when I have what really feels like irritated lungs with a chest that tightens up if I move around? Any ideas anyone?

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  • I can relate to what you are describing here. I've certainly had times where the actual PF reading belied the way I felt. Anyway, for what its worth here is my unscientific & completely based on guesswork theory.

    I think that maybe what has happened for you is that you've probably inhaled bits of dust & debris (masks are far from 100% guaranteed) & have probably just irritated your airways. The PF reading captures the maximum amount of air you can exhale. That is reduced when the inflammation in your airways causes constriction thus reducing the rate that the air can get out.

    In your case maybe you simply have an irritation not an inflammation. Of course once can become another over time but non-asthmatics can have irritated chests & lungs.

    If you find out the truth though let me know! I've always found it a bit baffling.

  • Thanks for that. The thing that still really baffles me is that things calmed down this morning after I took ventolin - which is suggestive that something was going on - but I never felt the need to take it during the infection when my peak flow reading dropped. I had it by my bed just in case I had issues during the night, but even then I didn't need it.

    If I do find an answer I will post it.

  • I think my consultant came up with the technically correct view a while ago. She told me..."they are very complicated things are lungs". That's probably the explanation :D

  • My husband (an engineer) has just told me that I obviously have faulty piping. Given that for much of the past two years I've been under the care of a consultant gastroenterologist as well, he might have a point😄.

  • If your small airways are irritated it doesn't show up on your peak flow! Peak flow is for large airway function. AsthmaUK nurse told me this last week :D

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