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Peak Flow Meter

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A peak flow meter for asthma is like a thermometer for a fever. Both are tools to help monitor what is going on in your body. For instance, there may be times when you feel "feverish," but when you take your temperature with a thermometer it is normal. With asthma, sometimes you may feel your breathing is fine, but when you measure it with a peak flow meter your lung function is slightly decreased.

The readings on a peak flow meter tell you how open your airways are, so you can better manage your asthma.

What Does a Peak Flow Meter Do?

A peak flow meter is a portable device that measures air flow, or peak expiratory flow rate (PEFR). It can be used to:

  • Find out how severe your asthma is
  • Check your response to treatment during an acute asthma episode
  • Monitor progress in treatment of chronic asthma and provide information for any changes in your therapy
  • Detect worsening lung function and avoid a possible serious asthma flare-up

A peak flow meter can help you and your allergist/immunologist, often referred to as an allergist, evaluate how severe your asthma is at any point in time. With a peak flow meter, you can often see a drop in your readings even before your symptoms (like coughing or wheezing) get worse. Decreases in peak flow may show that you need to increase your medication.

Another measure of asthma control is peak flow variability. For many people with asthma, symptoms are usually worse at night. By consistently monitoring nighttime peak flow measurements, you can tell how well your asthma is controlled. A decrease of 15% or greater from your usual measurement may be a sign of nighttime asthma. A person without asthma or with well-controlled asthma will consistently blow peak flows that vary less than 15%.

How to Use a Peak Flow Meter

Blow hard on the meter to get the best reading possible, and repeat this three times. Record the best of the three trials. All three measurements should be about the same to show that a good effort was made each time. This is especially important if you are evaluating your child's asthma.

Follow these steps:

  • Make sure the device reads zero or is at base level
  • Stand up (unless you have a physical disability)
  • Take as deep of a breath as possible
  • Place the meter in your mouth and close your lips around the mouthpiece
  • Blow out as hard and as fast as possible (one to two seconds)
  • Do not cough, spit or let your tongue block the mouthpiece
  • Write down the reading
  • Repeat two times, and record the highest of the three numbers in your chart

Keep a chart of peak flow readings to track your asthma symptoms. Peak flow meters need some care, so make sure to follow the cleaning instructions.

Your allergist may ask you to record your peak flow before and after using your rescue inhaler. If your medicine is working, you should see an improvement in your reading.

Finding Your Personal Best Reading

Although your predicted "normal" peak flow is determined by your height, age and gender, you should measure your asthma control by comparing your daily peak flow recordings with your "personal best" reading. Your personal best is the highest peak flow number you can get over a two to three week period when your asthma is under good control.

To determine your personal best:

  • Always use the same peak flow meter
  • Record your peak flow twice a day for two weeks
  • Ignore values that are very different from the rest

Traffic Light System

Once you and your allergist have found your personal best peak flow, you should make every effort to maintain values within 80% of this number so you feel your best. The following traffic light system can serve as an easy guide:

Green zone-Peak expiratory flow rate (PEFR) 80% to 100% of personal best. All systems "go." You are relatively free of symptoms and can maintain your current asthma management program.

Yellow zone-PEFR 50% to 80% of personal best. "Caution," as your asthma is worsening. Contact your allergist to fine-tune your therapy.

Red zone-PEFR below 50% of personal best. "Danger," your asthma management and treatment program isn't controlling your symptoms. Use your inhaled bronchodilator. If peak flow readings do not return to at least the yellow zone, contact your allergist.

Successful control of your asthma depends upon a partnership between you and your allergist. If you monitor your peak flow, your allergist can use this data to design and adjust your medication to keep your asthma under control.

Healthy Tips

  • A peak flow meter for asthma is like a thermometer for a fever. It helps monitor what's going on inside your body.
  • Blow hard on the meter to get the best reading possible, and repeat this three times. Record the best of the three trials.
  • Keep a chart of peak flow readings to track your asthma symptoms.
  • After finding your personal best reading, use the traffic light zones (red, yellow and green) as guidelines to manage your asthma.