What is a Peak Flow Meter?
A peak flow meter is a diagnostic tool used to monitor how well the lungs are functioning. It measures the rate at which air is expelled from the lungs. When several readings are taken over a period of weeks or months, one can determine if the lungs are stable or getting worse.
The peak flow meter consists of a tube that you blow into and a scale that indicates how much air was expelled from the lungs in a given period of time. It is small enough to fit in the palm of the hand. Most peak flow meters are cylindrical in shape, but there are a few digital peak flow meters that are more compact.
How to Use a Peak Flow Meter
To use the peak flow meter, set the scale on the meter to zero and hold the meter firmly. Take a deep breath and blow as hard as you can into the peak flow meter. Then, record the reading. To accurately measure the peak expiratory flow, which is the maximum rate of exhalation, a total of three measurements is recommended. So, reset the scale to zero, take a deep breath, and blow once again into the meter. Record the measurement and repeat for a third time. It is important to only blow air into the meter. If any saliva or water enters the meter, the reading could be affected.
Results of a Peak Flow Meter Test
A peak flow meter displays the result as a unit of volume per a unit of time. Specifically, the unit of the peak flow meter scale is liters per minute. Each reading is compared with the initial or baseline reading, which is taken when you are breathing without any symptoms. Normal readings of peak flow meters depend on a person's age, sex, and height. For example, a 30 year old male that is 5'10'' tall should have a reading close to 622 liters per minute. Check the charts below for normal peak flow values (click on images to enlarge).
Normal readings of peak flow meters are within 80-100% of the baseline reading. These readings are categorized in the green peak flow zone, which indicates stable lung function. When the readings are between 50 and 80% of the baseline reading, they are categorized in the yellow peak flow zone. This zone indicates a worsening in lung function. Anything below 50% of the baseline reading is in the red peak flow zone. Emergency medical treatment is usually required at this stage.
Causes of Abnormal Readings
There are several causes of abnormal peak flow meter readings. Any lung condition that decreases air flow will result in abnormal readings. Asthma, chronic obstructive pulmonary disorder, and emphysema are some of the conditions that will affect peak flow meter readings.
1. "Peak Flow Meter." Mayo Foundation for Medical Education and Research. https://www.mayoclinic.com/health/peak-flow-meter/MY01116/DSECTION=results
2. "The Peak Flow Meter." Health Information Publications. https://www.ehealthmd.com/library/asthma/asthma_peakflow.html
3. "Table of Normal Peak Flow Values." Partners Asthma Center. https://www.asthma.partners.org/newfiles/Appendix2.html