Asthma: The Peak Flow Meter

The peak flow meter is an important device that can give you valuable information about your air passages. Peak flow measurements provide a very simple way of measuring how quickly air can be forced out of the lungs.

Why Should I Do Peak Flow Monitoring?

Measurements of forced expiration are important in the overall assessment of lung function and are commonly used in pulmonary function testing.

  • Peak flow monitoring gives a valuable early warning sign for asthma that may be getting worse. Sometimes peak flow values decrease for hours, or even a day or two, before an attack is noticed. This early warning sign can be seen in the daily record of peak flow values. Because peak flow values are actually measured, they are objective and more reliable than feelings of “tiredness” sometimes experienced by people with asthma.
  • Peak flow monitoring is very sensitive and can help you communicate with your doctor. Keeping a diary of these measurements gives your doctor a written record of the condition of your breathing passages. The record you keep provides valuable information about how you’re doing and how well your asthma medications are working.
  • Peak flow monitoring gives important information that allows your doctor to adjust your medication if needed. The record also tells the doctor when emergency care may be needed to control an asthma episode that is worsening.

How-To Information

How often should you take a peak flow reading?

It depends on the plan your doctor has worked out.

  • If the asthma is quite mild, the doctor may suggest using the meter only when you are wheezing, or feel an attack is coming on.
  • Peak flow readings are useful when starting on a new medicine, because the peak flow readings will show clearly how well the medication is working.
  • If the asthma is quite severe, your doctor may want you to use the meter daily, at the time of day when the asthma is usually worst.
  • Many people take peak flow readings once or twice a day, usually in the morning before taking their medication and in the evening before going to bed. Whatever schedule your doctor suggests, try to take your peak flow readings at the same time each day to produce an accurate record.

How-To Information

How do I use the peak flow meter?

  • Have an empty mouth…no gum or food.
  • Stand up, if possible.
  • Set the meter at “zero.”
  • Hold the meter correctly, so fingers don’t get in the way.
  • Take a really deep breath, with the chest puffed up as far as it can go.
  • Close lips around the mouthpiece, with the tongue out of the way.
  • Blow as hard and fast as possible, as if blowing out candles on a cake.
  • The arrow will move until it points to a number on the scale. This is the peak flow number.
  • Make a note of the peak flow value next to the indicator (or the zone color on the meter). Your doctor may have attached a “Zone Indicator” of some kind to the meter so that you can record the “color” of the peak flow that you achieved.
  • Reset the indicator back to “zero” at the bottom of the scale.
  • Repeat the entire process two more times and write down best of three numbers in the daily record chart provided by your doctor. Note the date and time.

Remember to take a deep breath and blow as hard as possible into the meter to get the highest possible number. Do not spit into the flow meter because this will result in an artificially low value for peak flow.

Your “personal best” peak flow rate is the highest rate you can reach regularly when you are symptom-free. To determine this value, take your peak flow rates for a week when you wake up and before your evening meal. At each of these times, record the best number of your three tries.

Need To Know

How do I know if I’m using the meter correctly?

  • Watch: Make sure your chest puffs out, not your cheeks.
  • Listen: There should be no whistling noises from the meter.
  • Record: Look at the numbers on the scale and keep a record.
  • Clean: Keep your peak flow meter clean. Wash the plastic body in warm water at least once a week. Let air dry

What Do The Numbers Mean?

Many doctors recommend a three-zone system based on your “personal best” flow rate. This value is the highest peak flow measurement you can achieve on a day when your asthma is under good control.

  • The green zone: This includes readings higher than 80% of your best peak flow rate.
  • The yellow zone: This indicates you are able to achieve only 50% to 80% of your personal best peak flow rate.
  • The red zone: Your are able to achieve only half, or less than half, of your personal best peak flow rate.

Your goal is to stay in the green zone as long as possible. If you enter the yellow zone, follow your plan so that you do not enter the red zone.

  • If your peak flow reading is in the safety or green zone: This peak flow reading indicates there is no problem and suggests that current treatment is working.
  • If your peak flow reading is in the caution or yellow zone: A reading in the caution zone means that the asthma is worse, even if you feel fine and look well. Now you need to act on the plan worked out with your doctor – give or increase a particular medication or prepare for an attack.

    Your asthma action plan should make clear when the doctor is to be contacted. In many cases, this is not necessary unless readings repeatedly enter the Caution Zone, or stay there even after the treatment prescribed in your plan has been given.

  • If your peak flow reading in the danger or red zone: This means you are able to achieve only half, or less than half, of your personal best peak flow rate. It often means that an asthma attack has begun.

    Your plan should make clear what you need to do. This will include specific medication to be taken immediately. You should get in touch with your doctor if the medicine doesn’t stop the attack, or go immediately to the emergency room.

Need To Know

Do not rely on the numbers alone when using a peak flow meter. You must also make note of your symptoms. Sometimes the peak flow numbers are within your normal range but asthma symptoms are still present. This could be a signal to your doctor that your medication dosage needs to be adjusted.

Nice To Know

Q. How accurate are peak flow meters?

A. When used correctly, peak flow meters are excellent tools that reflect the state of the lungs, but you need to treat the device with respect. Keep it clean, use it as directed, check it frequently for damage, and it will give accurate measurements. However, remember that symptoms are just as important as numbers. In some cases, you can get a good peak flow “score” even when you are having symptoms such as difficulty in sleeping at night. If that’s the case, make a note of the peak flow numbers and talk to your doctor.


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