Measured during spirometry
Forced expiratory volume (FEV) measures how much air a person can exhale during a forced breath. The amount of air exhaled may be measured during the first (FEV1), second (FEV2), and/or third seconds (FEV3) of the forced breath.
Forced vital capacity (FVC) is the total amount of air exhaled during the FEV test.
FEV$_1$/FVC ratio: represent the proportion of a person’s vital capacity that they are able to expire in the first second of forced expiration to the full vital capacity.
- Normal values are approximately 80%.
Predicted normal values can be calculated online and depend on age, sex, height, and ethnicity as well as the research study that they are based upon.
A derived value of FEV1% is FEV1% predicted, which is defined as FEV1% of the patient divided by the average FEV1% in the population for any person of similar age, sex and body composition.
Forced expiratory volume is the most important measurement of lung function. It is used to:
- Diagnose obstructive lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). A person who has asthma or COPD has a lower FEV1 result than a healthy person.
- See how well medicines used to improve breathing are working.
- Check if lung disease is getting worse. Decreases in the FEV1 value may mean the lung disease is getting worse.