How to Use a Peak Flow Meter and How to Interpret Peak Flow Meter Readings

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What Is A Peak Flow Meter?

Asthma is a common medical condition which causes its sufferers to experience breathing problems due to constricted and/or swollen airways, among other symptoms. A peak flow meter is a very simple device that allows those who have asthma to easily and regularly monitor how well their lungs are performing by measuring their maximum exhale flow rate (which is described in more detail below). This information is helpful because it allows these individuals to determine things like whether their symptoms are about to become worse, when to take their medicine, whether their medicine or its dosage may need to be changed, or when a trip to the doctor is in order.

How To Use A Peak Flow Meter

When you visit your local pharmacy, you likely will see that there are many different brands of peak flow meters to choose from. While it is not a goal of this article to recommend any particular brand, you should take comfort in knowing that most peak flow meters are easy to use and are operated more or less in the same manner as one another. The typical steps for using a peak flow meter and determining a peak flow rate are as follows:

  • Set the sliding mechanism on the meter to its lowest value, which is usually zero
  • While standing erect, take a deep breath and insert the mouthpiece of the meter into your mouth
  • Blow a quick, full blast of air into the meter
  • Observe the position on the number scale to which the sliding mechanism moved and record the corresponding number in your asthma journal or wherever you keep your asthma records (along with the date and time of the reading, of course)
  • Repeat the prior four steps two more times (all three readings should be fairly close in value; you have made an error if they are not)
  • Consider the highest, and not average, value of the three readings to be considered your actual flow rate for that particular date and time

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How To Interpret Peak Flow Meter Readings

The first step that you must take before you can best interpret your peak flow meter readings is to establish what is your “normal”, or “target”, flow rate reading_._ It is important to note that a reading that is normal for someone else may not necessarily be normal for you. Factors such as age, height, and sex, for example, influence a person’s normal flow rate, so these factors must be taken into account. Based on your own particular personal information, you can get an estimate of what your particular normal flow rate should be by consulting with your doctor, who has access to “expected flow rate charts” that will guide her in making that determination. Further, once you take several readings over the course of many days, you should begin to get a better understanding of your normal flow rate.

Once you have determined what your normal flow rate is, it will be important to be able to spot any significant deviations from this target flow rate in your future readings and to quickly recognize exactly what you need to do at those times that there are significant differences. This can be achieved simply by placing the highest flow rate that you achieve into one of three zones, a green zone, a yellow zone, and a red zone, and acting accordingly whenever you are in a particular zone, such as follows:

  • Green Zone. If your highest reading of the three readings is 80 to 100 percent of your normal flow rate, you are in the “green zone”. This means that your asthma is under control and therefore that no changes to your medicine or other treatment courses need to be made.

  • Yellow Zone. If your highest reading of the three readings is 50 to 80 percent of your normal flow rate, you are in the “yellow zone”. This is unacceptable and you simply cannot stand in the yellow zone. You should establish with your doctor ahead of time exactly what steps you should take when you are in the yellow zone and add this information to your asthma plan. For example, you may be instructed to take action to clear your airways by altering how or at what times you take your asthma medicine. As another example, your doctor may also recommend that you lie down (or sit down) and rest comfortably, or take some other relaxation step, until such time that your flow rate returns to the green zone. Once you are back in the green zone, you may be advised that you can resume your normal activity (while being sure to continue to regularly monitor your flow rate).

  • Red Zone. If your highest reading of the three readings is less than 50 percent of your normal flow rate, you are in the “red zone” and this is a very dangerous zone to be in. If you are in this zone, you may be on the cusp of suffering a full asthma attack. You therefore need to immediately take the steps that you and your doctor work out ahead of time (again, which you can keep handy in your asthma plan). These steps are likely to include, for example, use of a bronchodilator or oral corticosteroid drug to force your airways open. They also may include contacting your doctor right away to inform her of your condition.

This article is only meant to provide some basic advice regarding how to use a peak flow meter and how to interpret peak flow meter readings. It is not meant to replace the good advice of your doctor. Please use your peak flow meter only in a way that is consistent with her instruction.


American Lung Association, Measuring Your Peak Flow Rate:

Mayo Clinic, Peak flow meter:

Medline Plus, National Institutes of Health, How to use your peak flow meter: