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Tests & Procedures : Pulmonary

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Peak Flow Measurement

(Peak Flow Meter, PFM, Peak Expiratory Flow Measurement)

Procedure overview

What is peak flow measurement?

Peak flow measurement is a procedure in which air flowing out of the lungs is measured. The measurement obtained is called the peak expiratory flow rate (PEFR), or peak expiratory flow (PEF).

Peak flow measurement may be obtained using a spirometer, an instrument with a mouth piece that measures the amount of air breathed in and/or out and the rate at which the air is inhaled and expelled from the lungs. Peak flow may also be measured with a peak flow meter (PFM), a portable, hand-held device. Both devices take the measurement as an individual forcefully blows into the mouthpiece of the device.

Spirometry is usually performed in a doctor’s office, clinic, or a hospital. A peak flow meter is small and light enough to be used almost anywhere.

Photo of older man using a spirometer

There are several types of PFMs available. However, it is important that one continues to use the same type of PFM on a consistent basis, as the PEFR can vary among different brands and types of meters.

Photo of a peak flow meter

Peak flow measurement using a peak flow meter is particularly useful for individuals with asthma. During an asthma flare-up, the large airways in the lungs slowly begin to narrow. This slows the speed of air leaving the lungs. A peak flow meter, when used properly, can reveal narrowing of the airways well in advanced of an asthma attack. Peak flow meters can help determine:

  • When to seek emergency medical care

  • The effectiveness of an asthma management and treatment plan

  • When to stop or add medication as directed by a doctor what triggers the asthma attack (such as exercise-induced asthma)

Other related procedures that may be used to diagnose problems of the lungs and respiratory tract include chest X-rays, bronchoscopy, bronchography, chest fluoroscopy, chest ultrasound, lung biopsy, lung scan, mediastinoscopy, oximetry, positron emission tomography (PET scan), pleural biopsy, pulmonary angiogram, pulmonary function tests, sinus X-ray, and thoracentesis. Please see these procedures for additional information.

Anatomy of the respiratory system

Illustration of the human respiratory system

The respiratory system is made up of the organs involved in the interchanges of gases, and consists of the:

  • Nose

  • Pharynx

  • Larynx

  • Trachea

  • Bronchi

  • Lungs

The upper respiratory tract includes the:

  • Nose

  • Nasal cavity

  • Ethmoidal air cells

  • Frontal sinuses

  • Maxillary sinus

  • Larynx

  • Trachea

The lower respiratory tract includes the lungs, bronchi, and alveoli.

What are the functions of the lungs?

The lungs take in oxygen, which cells need to live and carry out their normal functions. The lungs also get rid of carbon dioxide, a waste product of the body's cells.

The lungs are a pair of cone-shaped organs made up of spongy, pinkish-gray tissue. They take up most of the space in the chest, or the thorax (the part of the body between the base of the neck and diaphragm).

The lungs are enveloped in a membrane called the pleura.

The lungs are separated from each other by the mediastinum, an area that contains the following:

  • The heart and its large vessels

  • Trachea (windpipe)

  • Esophagus

  • Thymus

  • Lymph nodes

The right lung has three sections, called lobes. The left lung has two lobes. When you breathe, the air enters the body through the nose or the mouth. It then travels down the throat through the larynx (voice box) and trachea (windpipe) and goes into the lungs through tubes called main-stem bronchi.

One main-stem bronchus leads to the right lung and one to the left lung. In the lungs, the main-stem bronchi divide into smaller bronchi and then into even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli.

Reasons for the procedure

A peak flow meter (PFM) can assist with the management of asthma. It can provide you and your doctor with information about how open the airways are in your lungs. The PFM can detect small changes in the large airways before you start to wheeze.

Using a PFM every day will let you know when your peak flows are starting to drop. This allows you to make early changes in your medication or routine to help prevent asthma symptoms from worsening. The PFM can also identify the value at which you will need to call your doctor or go to the emergency room.

Photo of teen girl using peak flow meter

Peak flow meters are primarily used for individuals who have asthma. Your doctor may not recommend that a PFM be used unless your asthma is considered moderate or severe and you are managed with medication(s). Peak flow meters are also useful in children who have asthma.

The measurements obtained by PFMs may also be useful in evaluating other conditions such as:

  • Emphysema--a chronic lung condition that affects the alveoli, the smallest air sacks in the lungs

  • Chronic bronchitis--a long-term inflammation of the bronchi, which results in the increased production of mucous, and other change

Risks of the procedure

Because obtaining peak flow measurement is a noninvasive procedure, it is safe for most individuals. It is quick and inexpensive. However, the individual must be able to follow clear, simple directions.

Having to take in deep breaths to perform the procedure may cause you to feel dizzy, light-headed, or short of breath.

The procedure may trigger coughing and/or wheezing.

There may be risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Certain factors or conditions may interfere with the accuracy of peak flow measurement. These factors may include, but are not limited to, the following:

  • Coughing during the procedure

  • Poor seal around the mouthpiece while performing the procedure

  • A dirty meter

  • Blocking the mouthpiece with the tongue

  • Use of bronchodilator (opens the airways) medication

  • Use of a different type or brand of PFM, as the measurements may vary among brands and types of meters

Before the procedure:

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

  • Generally, no prior preparation, such as fasting, fluid restriction, or sedation is required. However, you may be asked to avoid eating a heavy meal before the test.

  • Notify your doctor of all medications (prescription and over-the-counter) and herbal supplements that you are taking.

  • Prior to beginning routine daily PFM monitoring, your doctor may instruct you to perform PFM on a more detailed schedule over two to three weeks in order to establish your “personal best” peak flow measurement. This personal best value will be used as a baseline for your routine measurements.

  • Based on your medical condition, your doctor may request other specific preparation.

During the procedure

Peak flow measurement may be performed one or more times daily at the same time of day, whenever you are experiencing early warning signs of an asthma attack, or as otherwise directed by your doctor. You should always use the PFM before taking asthma medication. Your doctor may recommend other times when using a PFM is useful.

Generally, peak flow measurement follows this process:

  1. Before each use, make sure the sliding pointer on the PFM is reset to the zero mark.

  2. Hold the PFM by the handle.

  3. Stand up straight.

  4. Remove chewing gum or any food from your mouth.

  5. Take a deep breath and put the mouthpiece in your mouth. Seal your lips and teeth tightly around the mouthpiece.

  6. Blow out as hard and as fast as you can. Remember, a “fast blast” is better than a “slow blow.”

  7. Note the number where the sliding pointer has stopped on the scale.

  8. Reset the pointer to zero.

  9. Repeat this routine three times. You will know you have done the technique correctly when the three readings are close together.

  10. If you cough during a measurement, you should repeat it.

  11. Record the highest of the three readings on a graph or in a notebook. Do not average these numbers together. This is called your “peak flow.”

  12. Use the peak flow meter once a day, or as directed by your doctor. Measure peak flows about the same time each day. A good time might be when you first wake up or at bedtime.

After the procedure

Any type of care after the procedure will be based on the results of the procedure. Your doctor will instruct you about your peak flow zones and how you should respond when your peak flow measurement indicates a particular zone.

What are peak flow zones?

Peak flow zones are based on the traffic light concept: red means danger, yellow means caution, and green means safe. These zones are different for each person. Your doctor will help determine your peak flow zones. The three peak flow zones include:

  • Green: This is the GO zone. The green zone is from 80 to 100 percent of your highest peak flow reading, or personal best. This is the zone you should be in every day. Measurements in this zone signal that air moves well through the large airways and that you can do the usual activities and go to sleep without trouble. You should continue to follow your asthma plan as directed by your doctor.

  • Yellow: This is the CAUTION or SLOW DOWN zone. The yellow zone is from 50 to 80 percent of your personal best. Measurements in this zone are a clue that the large airways are starting to narrow. You may begin to have mild symptoms, such as coughing, feeling tired, feeling short of breath, or feeling like your chest is tightening. These symptoms may keep you from your usual activities or from sleeping well. You should notify your doctor at this time. He or she may instruct you to increase or change your medications and give you additional instructions to help prevent your symptoms from worsening.

  • Red: This is the STOP zone. The red zone is less than 50 percent of your personal best. Readings in this zone mean severe narrowing of the large airways has occurred. This is a medical emergency and you should get help right away. You may now be coughing, very short of breath, wheezing both when breathing in and out, or having retractions. You may also have problems walking and talking. You should take your reliever medication now and call your doctor.

The goal of the peak flow zones is to recognize early symptoms of uncontrolled asthma.

If it is necessary for you to get a new PFM, you should obtain a new personal best value for the new meter.

Your doctor may give you additional or alternate instructions depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your doctor with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Academy of Allergy, Asthma and Immunology

American Academy of Pediatrics

American Lung Association

National Heart, Lung, and Blood Institute (NHLBI)

National Institutes of Health (NIH)

National Library of Medicine