A peak flow meter is a hand-held device that measures the maximum speed that air comes out of your lungs during a fast exhalation. There are numerous ways to measure peak expiratory flow and these devices can be either mechanical or electronic. Their accuracy tends to be limited but repeatability (i.e., the ability to give the same reading for the same flow rate) and durability are more important features for home use.
Why would you measure your peak flow?
A peak flow meter is one of the ways that are used to monitor the condition of your airways but to do this you will need to use it regularly and to keep a diary of readings.
How would you measure your peak flow?
To measure your peak flow you would:
- take as deep a breath as you possible can
- put the mouthpiece of the peak flow meter in your mouth
- seal your lips around the mouthpiece
- blow out as fast as you can for about a second
What is a normal peak flow?
You should measure your peak flow at least three times in a row and record the highest number. Normal values for peak flow from the NHANESIII study (Caucasian values) are:
What do these numbers mean?
Peak flow measurements are usually divided into zones:
Green Zone – 80% of normal and above
Yellow Zone – 50% to 80% of normal
Red Zone – Below 50% of normal
You should have a treatment plan from your physician for each of these zones that may involve increasing or decreasing the amount of medications you take. When your peak flows are exceptionally low you should contact your physician and even consider going to a hospital emergency room for treatment.
Should you have your own peak flow meter?
The only function a peak flow meter can perform is to measure very fastest rate that you can blow your air out. This is tends to correlate best with Asthma and for this reason peak flow monitoring is usually recommended for people with Asthma.
Note: 5% to 10% of individuals with Asthma have only minimal changes in peak flow despite much bigger changes in airway function and for these individuals it is better to regularly monitor their FEV1 with a spirometer instead.
Peak flow monitoring may also be useful for children and adults with Cystic Fibrosis, however the correlation between peak flow and airway condition is not as clear or consistent as it is for asthma.
Unless there is an asthmatic component peak flow does not correlate well with the condition of the airways in Emphysema, Chronic Bronchitis and Bronchiectasis.
Sarcoidosis can have both an airway component and a lung capacity component, and many individuals with this lung disorder also have Asthma. Depending on the mix of these components a peak flow meter may or may not be useful for individuals with Sarcoidosis.
For restrictive lung disorders like Pulmonary Fibrosis (IPF) and neuromuscular disorders like Amyotrophic Lateral Sclerosis (ALS) there is little value in monitoring peak flow.
How do you get a peak flow meter?
Your physician may either give you a peak flow meter or write you a prescription for one. Many insurance plans will pay for all or part a peak flow meter but usually only if you have asthma or COPD. Most pharmacies stock peak flow meters but they are also readily available for ordering on the internet (prices on Ebay and Amazon start in the $10-$15 range and go up from there).
Other things to consider:
Peak flow meters are not as accurate as the spirometers you would find in a doctor’s office or hospital. For this reason you should determine your own personal Green, Yellow and Red zones from the measurements you make and not necessarily from a chart. This also means that if you replace your peak flow meter with a new one, even if it is the same brand, you may need to re-determine your Green, Yellow and Red zones.
Expect to measure your peak flow regularly, not just when you aren’t feeling well. You need to know what your peak flow is on your good days as well as your bad days in order to be able to judge if a change in peak flow is important or not.
Expect that it will take some practice to learn the proper way to perform a peak flow maneuver. You need to blow your air out in a forceful huff and not in a cough (which can cause your peak flow measurement to be too high) or in a sigh (which can cause your peak flow measurement to be too low).
Consistency is important for you to be able to rely on your peak flow measurements. When you make your three daily measurements they should be within 10% of the best (highest) measurement. If there is a lot of difference (greater than 25%) between each of your daily measurements then peak flow monitoring may not be appropriate for you.
PFT Patient by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.