Peak expiratory flow rate

• Alternative Names

  Peak flow

• How the test is performed

  This test requires a peak expiratory flow monitor: a small handheld device with a mouthpiece at one end and a scale with a moveable indicator (usually a small plastic arrow).

  To perform this test:

  • Breathe in as deeply as possible.
  • Blow into the instrument's mouthpiece as hard and fast as possible.
  • Do this three times, and record the highest flow rate.
• How to prepare for the test

  Loosen any tight clothing that might restrict your breathing. Sit up straight or stand while performing the tests.

• How the test will feel

  There is usually no discomfort. Rarely, repeated efforts may cause some light-headedness.

• Why the test is performed

  The test is commonly used to diagnose and monitor lung diseases such as:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Rejection after a lung transplant

  Home monitoring can help determine whether treatments are working or detect when your condition is getting worse.

• Normal Values

  Normal values vary based on a person's age, sex, and size. Peak flow measurements are most useful when a person compares the number on a given day to his or her "personal best."

  A fall in peak flow can signal the onset of a lung disease flare, especially when it occurs with symptoms such as:

  • Increased cough
  • Shortness of breath
  • Wheezing

  Early treatment may be needed to prevent complications.

• What abnormal results mean

  Peak air flow during exhalation decreases when the airways are blocked (obstructed).

  Many patients can use peak expiratory flow monitoring to monitor their lung function at home. This can be very helpful, especially in asthma patients whose peak flow reading sometimes gets low before they develop breathing symptoms. If the fall in peak flow is treated early, symptoms can be avoided.

  If you note that your peak flow is decreasing, tell your health care provider.

• What the risks are

  There are no significant risks.

• Special considerations

  Peak expiratory flow rate measurements are not as accurate as the spirometry measurements performed in a health care provider's office. Small changes in your peak flow may not mean significant changes in your lung function.

• References

  National Asthma Education and Prevention Program Expret Panel Report 3: Guidelines for the Diagnosis and Management of Asthma. Rockville, MD. National Heart, Lung, and Blood Institute, U.S. Dept. of Health and Human Services; 2007. NIH publication 08-4051.

Review Date: 10/14/2009

Reviewed By: Andrew Schriber, MD, FCCP, Specialist in Pulmonary, Critical Care, and Sleep Medicine, Virtua Memorial Hospital, Mount Holly, New Jersey. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.