A peak expiratory flow rate (PEFR) measures how effectively you exhale. Also called a peak flow meter, this handheld device helps you document the amount of air and the speed at which you can forcefully breathe from your lungs.
Doctors will often recommend the peak flow meter if you have chronic obstructive pulmonary disease (COPD) or asthma. During an asthma attack, the air passages in the lungs will narrow, making it difficult to breathe. A peak flow meter is sensitive enough to detect these changes in your lungs for hours or even days before you notice asthma symptoms. Using a peak flow meter can help prevent a severe asthma attack.
Why Your Doctor May Suggest a PEFR Test
Your healthcare provider may suggest using a PEFR test to help you monitor and manage:
- Moderate or severe asthma
- COPD
- Sensitivity to ozone or air pollution
A peak flow meter is often part of an asthma treatment plan. It can detect tiny changes in large air passages before you start wheezing. Measuring your peak flow every day can help you and your doctor determine:
- When your airways start to narrow
- What is triggering an asthma attack
- How much medication you need
- When to start or stop using your inhaler
- When to seek medical attention
- If your asthma treatment plan is working
As you use the peak flow meter, you'll start to notice breathing patterns, including your personal peak flow. This is the highest reading out of three on your peak flow meter. A personal peak flow is different for everyone. Results depend on your age, height, and gender.
Preparing for a PEFR Test
Talk to your doctor before starting a daily test. He or she will create a schedule for you to follow that usually lasts two or three weeks. This is part of your treatment plan and helps you determine your personal peak flow measurement.
Make a list of any prescriptions, over-the-counter (OTC) medications, herbal supplements, and vitamins you take. Don't eat a big meal before you take the PEFR test and make sure you follow all of your doctor's instructions.
What To Expect
The PEFR meter is a handheld device you buy without a prescription. There are two types: a smaller or low-range meter for children and a larger or standard range for teenagers and adults. Both meters work the same way. Before you start, make sure the device is clean and the indicator is set to zero, or the lowest number on the scale. To start the test, follow these steps:
- Stand up and place the meter in your mouth between your teeth
- Take a big inhale
- Exhale once as hard and fast as you can to blow air into the meter
- Write down the number you see
- Repeat these steps two more times
Sometimes your tongue gets in the way of the mouthpiece or you might cough or sneeze. If that happens, retake the test. Once you've written down all three numbers, record the highest one.
Typically, you'll measure your peak flow once a day before taking any asthma medicines. If you're noticing any symptoms, it may be necessary to test more often. Use the same peak flow meter each time you test.
Interpreting Your PEFR Test Results
Each PEFR device will have three areas of measurement. These are called peak flow zones. They're identified with the following three colors.
Green. The green zone measures 80% to 100% of your highest reading. It's your personal best and the zone you should be in each day. When your lungs are functioning properly, you can exercise, perform daily tasks, and fall asleep without any symptoms.
Yellow. It's important to pay attention to a yellow reading. This means it's time to take action according to your asthma treatment plan. You may notice certain symptoms, like fatigue, coughing, a tight feeling in your chest, or shortness of breath. The yellow zone measures 50% to 79% of your personal peak flow.
Red. A red zone reading measures less than 50% of your best. It means your air passages have narrowed, and you need to get medical help right away. Symptoms include coughing, shortness of breath, and wheezing. It may be hard to walk or talk.
Possible Risks
PEFR tests are generally safe. But as with any medical device, there are some risks associated with this procedure, including:
- A dizzy or disoriented feeling while taking a deep breath
- Coughing or wheezing as a result of a forceful exhale
If you haven't used a peak flow meter before, it may take some time to adjust. If you're having any difficulties, talk to your doctor.