Peak Air Flow calculation?

[DustinS85]

I go to Medcape and it says the Peak Expiratory Flow for me is 648L/min and I go MD Calc and it says 614L/min. And the charts online say different than that. How can you know for sure what normal is? I am 183 centimeters or 72 inches tall and I am 32.

[Superzob]

Personally, I think too much is read into peak flow results. They are averages, based on population samples; if you take a different sample, you will get a different result, which probably explains the different averages you've come across. More importantly, peak flow is no guide to symptoms: there are many on this forum with good peak flows, but quite severe symptoms and, conversely, many with poor peak flows and virtually no symptoms. The moral seems to be: if you feel well, don't worry about your peak flow; if you don't, seek some medical advice.

[Lysistrata Administrator Community Ambassador in reply to Superzob]

Yes! I once had a triage nurse tell me my best peak flow could not possibly be over 600, because I am a woman and my predicted best is lower than that. I didn't have the breath for a stats lesson, but was strongly tempted to ask him if that also meant I couldn't possibly be 5'8" tall because the average UK woman is about 5'4"?

Perhaps if there were less obsession with peak flow, we wouldn't be doing so badly on asthma outcomes in the UK.

[Superzob in reply to Lysistrata]

And bees can't fly!

[EmmaF91 Community Ambassador]

Ignore the charts and go from your best. My best is almost double my predicted, so if I’m having issues I usually have to fight the ‘you’re pf is good your having a panic attack’ when my pf is at 50%. Once they realise this they treat accordingly.

Be aware that you’re best can change as you gain control and as your PF technique improves (PF increases) but that as you age it will also slowly drop. Your best has to be hit in the last 6 months for it to count.

A lot of thing factor into your PF - history of high level/regular sports, playing wind instruments/singing, posture, body shape etc - mine increases by at least 60 when I stand compared to sitting and I used to be a national level trampolist/gymnast which is why it’s so high. (It’s higher than most of my friends, nurses and docs - usually only lanky lads can beat me 😂)

PF will also naturally fluctuate during the day - I’m usually best at 11AM and 3/4PM and worse and night/early morning esp 4AMish if I’m ill.

‘Normal’ is overrated as I doubt the charts accommodate for all the variables. On here it seems that people are either high or low compared to the expected charts. Work out what your best is, then go off symptoms as well as PF.

Hope this helps and clears things up a little x