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ChocolateReigns's avatar

Does anyone have experience with peak flow meters? I have some questions about what's considered "normal". (read on) questions about?

Asked by ChocolateReigns (5619points) March 3rd, 2011

I’ve posted about the breathing problems I have on here before, and last week I went to a respiratory therapist to get some tests done. She was the most helpful out of the 5 people I’ve seen for this. She said the tests were normal, but obviously I’ve still got something wrong going on. I got a better inhaler (she thought maybe the current one just wasn’t strong enough) and a peak flow meter to have some actual numbers and statistics to compare with.
She said for a female my height, weight, and age, my peak flow numbers should be somewhere around 400 liters per minute. Well, in the week and a half that I’ve had the meter I’ve never gotten above 370 lpm and I hardly ever get above 340 lpm. In one day, I can go from 300 when I wake up, to 320 at lunch, then down to 290 in the afternoon, and finally, just before I go to bed, I might be at 340. I’ve been writing down my symptoms, the peak flow numbers, and the time for this past week and a half. Looking back at the information, it looks like there’s absolutely no rhyme or reason to when my symptoms flare up, when the numbers are low, or whether or not they happen at the same time.

Sorry, yes, this was a lot of reading…
Here’s my actual questions:
1) Is it normal that my peak flow numbers fluctuate so much during the day?
2) The “normal” peak flow numbers for a female my size and age are about 400 liters per minute. I would think that I hardly ever get within 50 lpm of that is bad. Is it all right? Is this a bit alarming?

Thank you so much, guys!

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5 Answers

leogirly4life's avatar

I hope this helps you out. I know nothing but your issue but I looked around for a hopefully helpful link. Best of luck!


Lightlyseared's avatar

1) Yes, it is perfectly normal for peak flow values to fluctuate during the day just as it’s perfectly normal for your blood pressure, your heart rate and your respiration rate to fluctuate during the day depending on what you are doing etc.

2) As far as I remember (an I admit I don’t have much to do with repiratory patients these days) the 400 l/min you’ve been quoted would be the predicted average for a healthy women and readings 85 l/min less are still considered normal so 370 l/min is very respectable and nothing to worry about. Someone with asthma might not ever be able to get near the actual target. What is important is that you keep a record of your personal best. Generally, if the average reading is ⅓ or more below your personal best then your asthma might not be well controlled so this helps the doctors work out if they need to adjust your meds.

LuckyGuy's avatar

@leogirly4life ‘s link had the same info I was going to tell you.

(Our company has designed various pieces of respiratory equipment over the years. Portable Emergency Ventilator, Peak flow and tidal volume indicators.)

First, you need to know your personal best. Call it 400 l/min for this example.
At any time you are in one of three zones: Green Yellow and Red.
The green zone is 80–100 of personal best, so 320 -400 l/min
The yellow zone is 50–80% of personal best or 200–320 At this level, use your emergency inhaler Albuterol or similar.
The red zone is <50% or <200 use emergency inhaler and get help.
There are more details in the info above.

Your peak flow can change dramatically if you are exposed to an allergen. If you are allergic to wine for example, after a glass, your peak flow can drop to 60% and you might not even notice it.
Also be aware that there is usually a rebound after using some rescue inhalers. this means your peak flow will increase and may reach a max at 10–20 minutes but it will slowly decrease to potentially below 70% by the time 4 hours has passed.
Different inhalers have different characteristics. Slower response, reduced rebound, etc. The data sheet will tell you what to expect.

ChocolateReigns's avatar

BTW, I didn’t mean to put that “questions about?” at the end. oops.

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