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Peak Flow - Explained

Peak flow measurements are one of those things that long-time lungers mostly-hate. So, while a lot of literature floats around the Web about checking your peak flows, your doctor may never mention it to you. I mean, an objective measure of your asthma seems like a pretty good idea, right? I agree… sometimes!

What are peak flow measurements?

Peak Expiratory Flow (known as PEF, Peak Flow, or simply PFs by many with asthma), is just a fancy way of explaining a way to measure the amount of air that comes out of your lungs as fast as you can force it out. Stay with me here. By exhaling as fast as you can into a peak flow meter, the device translates that into a “litres per minute” value. Peak flow meters come in both analog (or manual) versions that you move the measuring device with your exhalation, or digital versions, which can store data and present it as a number on a screen on the meter. By checking your PEFs for a week or two while you’re feeling good, you can determine a baseline PEF value. From there, you’ll be able to make this data actionable.

What’s the point of measuring peak flows?

Sometimes, your numbers might not actually jive with how you’re feeling. For me, if I’m sick, I might actually feel like I am breathing okay-ish aside from cold symptoms, but my lung function is lower than normal. In this case, peak flows help me to know when I need to take extra rescue medicine. Peak flows can also help you see how well you’re responding to a new treatment, or determine patterns in your breathing—for example, for people with asthma, peak flow is often worse in the morning and better in the evening. Your doctor might use this information to ensure you have better medication coverage at different times in the day based on your peak flow measurements over time.

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How does logging peak flow help with asthma?

Logging peak flows can make you more aware of daily fluctuations, or changes, in your asthma. Sometimes, they can clue you in to whether or not you might be getting sick. Your doctor may have you take peak flows for a week or so before switching medications, to see if a new drug works better for you or not. By establishing a baseline number, you can then break your values into “zones”, which can be used in tandem with an Asthma Action Plan.
An Asthma Action Plan is created by your doctor to help you manage your own asthma better. It will, in writing, explain what medicines to take in different situations, or what action to take if you get sick or have a bad flare. Asthma Action Plans correlate with the stoplight system: green, yellow, and red.

Green Zone - The Green Zone means you’re “good to go”. At 80 to 100% of your personal best peak flow, you’ll feel the best you can, and be able to do all the things you want to do. Take your daily medication as prescribed, and continue to avoid triggers as much as possible (as always, with the exception of exercise!

Yellow Zone - The Yellow Zone usually means you are having a flare or that or you’re getting sick. Your peak flow will drop to under 80 but above 50 or 60% of your personal best. You should take your rescue inhaler following your doctor’s instructions, but your doctor may also have you adjust medications based on this number, or call them for further instructions.
Sometimes, the Yellow Zone is divided into the upper and lower yellow zones. For example, your doctor may have you increase inhaled medicines for a day or two in the upper yellow, but start prednisone (oral steroids) in the lower yellow zone, in addition to taking more inhaled bronchodilator medicines, in order to avoid dipping into the red zone.

Red Zone - When your numbers hit under 50 or 60% of personal best, this is a medical emergency. You should follow your doctor’s instructions to either call them immediately or go straight to the hospital or urgent care centre for help. Take your rescue inhaler at the interval specified by your doctor.

Are peak flows helpful in managing asthma?

As a bit of a quantified self nerd, you’d think I’d love peak flows. Well, while I am pretty into turning a lot of aspects of my life—sleep, exercise, time spent on writing, and more—into numbers based on time and percentages, measuring peak flows isn’t super high on my priority list right now. I understand the importance (even if some of my doctors don’t). Some patients will find taking their peak flow really helpful, and others will not—it’s really a personal choice, unless your doctor has a really good reason to have you checking regularly (and there is nothing wrong with that!).
So, hopefully, having written this post will help me get back on track with using my own body as a science experiment and see if I can find now—after a couple years hiatus from regularly logging. I’m interested in seeing if I can find any new trends now… well, at least for a little while!

This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

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