Forced Expiratory Volume (FEV1) and Asthma

FEV1 is the maximal amount of air you can forcefully exhale in one second. It is then converted to a percentage of normal. For example, your FEV1 may be 80% of predicted based on your height, weight, and race. FEV1 is a marker for the degree of obstruction with your asthma:

  • FEV1 greater 80% of predicted= normal
  • FEV1 60% to 79% of predicted = Mild obstruction
  • FEV1 40% to 59% of predicted = Moderate obstruction
  • FEV1 less than 40% of predicted = Severe obstruction
Man about to breath into a forced expiratory volume machine
Science Photo Library Collection / Brand X Pictures / Getty Images

FEV1 is one of the most common indices used to assess airway obstruction. It is automatically calculated during spirometry or pulmonary function testing. It is calculated using a spirometer.

How FEV1 Is Used In Asthma Treatment

Most commonly forced expiratory volume will be ordered by your doctor as part of complete pulmonary function tests. Your doctor may do this to assess your symptoms before an asthma diagnosis has been made or monitor your asthma control as part of your asthma action plan. Symptoms such as the following may trigger your doctor to order these tests:

In years past, the only way to get a forced expiratory volume was a machine in the office. With the advent of new technology, it is now possible to get an FEV1 on a home-based machine- meaning that you and your doctor could use this as part of your home monitoring for asthma.

This test is distinguished from data you obtain from performing peak flows. A peak flow meter gives you a number that estimates the amount of air that you can push out of your lungs with a forceful exhalation. When used repetitively over time, changes in your peak flow can let you know that your asthma is not under as good of control as you might want.​​​

Many asthma action plans use peak flows as one of the triggers for action on your part. You will determine what your personal best exhalation is and then base your action on a percentage of that number. So it is not really the actual number that is important in this case, but the relative changes that you see over time.

If you are going to use forced expiratory volume as part of your asthma action plan you will need to talk with your doctor about what sort of home spirometer might be best for you. There are a number of different models with different features and price points.

You will then need to monitor and record your FEV1 over time. You and your doctor will then need to place particular FEV1 readings into your green, yellow, and red zones of the asthma action plan.

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Article Sources
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  1. United SteelWorkers. Understanding Your Breathing Test Results. Worker Health Protection Program [internet]. 2013.

  2. Globe G, Martin M, Schatz M, et al. Symptoms and markers of symptom severity in asthma--content validity of the asthma symptom diary. Health Qual Life Outcomes. 2015;13:21. doi:10.1186/s12955-015-0217-5

Additional Reading
  • George RB. Clinical Pulmonary Function Testing, Exercise Testing, and Disability Evaluation. Chest Medicine, Essentials of Pulmonary and Critical Care Medicine. Lippincott Williams & Wilkins; 2005.

  • National Heart, Lung, and Blood Institute. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma