Forced Expiratory Volume (FEV1) and Asthma

Forced expiratory volume (FEV1) is the maximum amount of air you can forcefully exhale in one second. It is used to describe the degree of airway obstruction caused by asthma in a routine test called spirometry or pulmonary function testing, using an instrument called a spirometer.

FEV1 is calculated by converting the spriometer reading to a percentage of what would be predicted as normal based on a several personal factors. For example, your FEV1 may be 80% of predicted based on your height, weight, and race. Therefore:

  • FEV1 greater than 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.

FEV1 is not the same as peak flow volume, which is determined with a device called peak flow meter that estimates the amount of air you can push out of your lungs in a single, untimed forceful exhalation. When measured over time, changes in peak flow can be an indication of whether asthma is well controlled or not.

How FEV1 Is Used In Asthma Treatment

An FEV1 test is most likely to be ordered by a healthcare provider as part of complete pulmonary function testing. It may be done to assess symptoms before an asthma diagnosis has been made or to monitor asthma control as part of an asthma action plan. Your healthcare provider may order pulmonary function testing if you have certain respiratory symptoms, such as:

Although originally the only way to measure forced exhalation volume was in a healthcare provider's office, it is now possible to do so using a home spirometer, allowing you and your healthcare provider to use FEV1 testing as part of your home monitoring for asthma.

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 healthcare provider 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 monitor and record your FEV1 over time, after which you and your healthcare provider will place specific FEV1 readings into your green, yellow, and red zones of the asthma action plan.

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2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sharoon D, Edwards CW. Forced expiratory volume. In: StatPearls. Updated September 14, 2020.

  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

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