Peak expiratory flow is the maximum speed at which a person can exhale air from the lungs in a single breath. Lung function tests allow this rate to be measured as an indicator of how airways are functioning. This data can help patients and physicians determine how diseases such as asthma and chronic obstructive pulmonary disease (COPD) are affecting the lungs at any given time. Peak expiratory flow readings are taken when the patient is exhaling as hard and as fast as possible.

Peak flow meters are small, hand–held devices that allow patients to monitor changes in the status of their airways. Patients breathe into the mouthpiece at one end and receive a reading on a scale with an indicator. Lower readings correspond with higher airway obstruction.

Patients should regularly use a peak flow meter to monitor their airways, regardless of how they are feeling. A reading that is 20 percent below normal, or a change from the patient's usual range, can warn of an impending asthma attack or other looming respiratory distress. This can be a warning sign to patients to take certain medications or to contact their physician.

Patients should record the results of peak flow meter tests in an asthma diary that tracks their condition. The result of any test can be compared to a personal best score, which is the highest peak–flow measurement recorded over a two–week period when a condition is under control. Patients have their condition under “good control” when they feel good and are not showing symptoms.

Peak expiratory flow is the maximum air speed a person can achieve during forced exhalation that begins with the lungs fully inflated. Many patients with asthma, chronic obstructive pulmonary disease (COPD) or other respiratory disorders regularly measure this ability to indicate how well their airways are functioning. Lower readings may indicate an impending asthma attack or other looming respiratory distress before symptoms develop. In fact, the device can warn of an attack that is two or three days away.    

Peak expiratory flow readings are taken when the patient is exhaling as hard and as fast as possible. Patients measure their peak expiratory flow rate (PEFR) with a peak flow meter. People with moderate to severe breathing problems should measure their PEFR regularly, and should carry their meter with them at all times.  

Peak flow meters are also used to measure peak flow variability. This is a measure of the change in peak flow readings from test to test. Patients who have symptoms under control should have peak flow readings that consistently vary less than 15 percent.

PEFR readings are used in conjunction with asthma action plans, which are written, color–coded guidelines on when to use medication and/or seek medical care. An asthma action plan is prepared with the help of a physician. It compares a patient's best reading with their current reading.

Patients may also use these readings to uncover the effects of allergens or irritants on their breathing ability. For example, peak flow readings may drop during seasons when airborne allergens such as pollen are prevalent.

Peak flow meters are available through a healthcare provider or at a local pharmacy. They are easy to use for most people, and can generally be used by children ages 5 and older. Some children may be able to use the meter at age 3. While the standard range peak flow meter is reliable for older children, teenagers and adults, young children have smaller airways and often require a low range meter. Parental supervision of peak flow measurements is important for evaluating the condition of a child’s asthma.

It is important to use the same peak flow meter for each test. Studies have shown that measurements recorded by different brands of peak flow meters vary widely from one another. Patients who switch to a different peak flow meter will have to establish a new personal–best baseline, which is the highest peak-flow measurement recorded over a two-week period when a condition is under control. This score will serve as a benchmark against which to measure asthma progress. The different expiratory rate is what is important to measure during this test; therefore it is necessary to know whether rate changes are due to a new peak flow meter or actual airflow changes.

Patients should record the results of peak flow meter tests in an asthma diary that tracks their condition. Patients should bring their asthma diary to any visits with their physician. Examining information in the diary can help a physician determine the effectiveness of a treatment plan and whether or not any changes are necessary. The recorded PEFR measurements can also be compared to readings taken with equipment in the physician's office to ensure accuracy.

Asthmatics using a peak flow meter to determine the status of their condition should take the following preparatory steps:

• Avoid eating a heavy meal for three hours before taking the test
  
  
• Sit up straight or stand to aid in taking as deep a breath as possible
  
  
• Remove any gum or food from the mouth

Patients who measure their peak expiratory flow once a day should do so first thing in the morning, before using any bronchodilator medication. It is also a good idea to take a second reading in the evening. Usually, peak expiratory flow levels are higher in the evening. Worsening levels at night may indicate that a patient has nocturnal asthma and needs an improved asthma treatment plan.

In addition, patients should take a peak flow meter reading each time symptoms occur and when a rescue medication (such as a short-acting inhaled beta2 agonist) is used – to be sure the medication is working properly. Patients should see an improvement in their peak flow reading after taking the medication. Additional testing may also be required when the patient has a respiratory infection.

Patients using a peak flow meter should use the following steps:

• Move the indicator to the bottom of the numbered scale
• Attach mouthpiece to peak flow meter and stand
• Place mouth on mouthpiece and inhale deeply
• Close lips and teeth tightly around mouthpiece, being careful not to stick the tongue inside the tube
• Blow out hard and fast for no more than one second

The peak flow meter will provide a numerical result during or just after the exhalation. Patients should record the number, then repeat the process twice more. The highest number registered during the three trials should be used to establish a test score. Patients who cough while taking the measurement should disregard the results and take a new measurement. Coughing is likely to cause inaccurate measurements.

A physician should indicate the best times to use the peak flow meter. If a patient cannot use a peak flow meter during this optimal time each day, the patient should try to at least use the meter at the same time each day for consistent results. Use of a peak flow meter will also likely be incorporated into an asthma action plan, which is a written set of guidelines and procedures to follow in the event of an asthma attack.  

Patients will need to record a “personal-best” score when using a peak flow meter. This score will serve as a benchmark against which to measure asthma progress. Although there are predicted “normal” peak flow levels based on height, age and gender, it is better to establish a personal score.

To establish a personal-best score, patients should take peak flow readings at least once a day for two to three weeks. A physician will determine the best time of day to take the readings (usually between noon and 2 p.m.).

The highest peak-flow number recorded during a period when symptoms are under “good control” (when a patient feels good and is not manifesting symptoms) serves as the personal-best score.

Personal-best scores should be remeasured each year to account for growth (in children) and changes in the status of the disease.

Once a personal-best score has been established, ranges are set to help the patient react to subsequent scores. Scores are categorized by three levels:

• Green zone: A score that is between 80 percent and 100 percent of a patient’s personal-best score means no symptoms are present.
  
  
• Yellow zone: A score that is between 50 percent and 80 percent of a personal-best signals that caution is necessary. Follow a physician’s advice for which steps to take.
  
  
• Red zone: A score that is below 50 percent of a personal-best score signals a medical alert. A patient should use an inhaler immediately and a physician should be contacted right away.

Patients should be sure to wash their meter after each use according to the manufacturer’s directions. This will help prevent the growth of bacteria and fungi.

Peak flow meter tests present no significant risks to patients. However, some lightheadedness may result from the repeated blowing that is part of the test. Coughing and wheezing may also occur.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to peak expiratory flow:

1. Could I benefit from using a peak flow meter?
   
   
2. Where can I get a peak flow meter? Can you recommend a brand?
   
   
3. Can you show me how to properly use my peak flow meter?
   
   
4. How can I establish my personal-best baseline?
   
   
5. How often should I measure my peak expiratory flow?
   
   
6. At what times should I use my peak flow meter?
   
   
7. Do I need to carry my peak flow meter with me at all times?
   
   
8. What should I do when my score is in the yellow zone?
   
   
9. What should I do when my score is in the red zone?
   
   
10. What do the recordings in my asthma diary indicate?
    
    
11. I just purchased a new peak flow meter. Does this change anything?