Forced vital capacity, or FVC, is one of the measurements taken during a spirometry test, a type of pulmonary (lung) function test that helps doctors determine the presence and severity of lung disease. FVC reflects the amount of air you can forcibly exhale, after taking the deepest breath possible. Once your FVC is determined, your doctor will compare your measurement to that which is predicted, based on age, height, sex and weight. A decreased FVC is associated with both obstructive and restrictive lung diseases. Check out what these terms mean below.
When youâ€™re unable to expel all the air from your lungs, youâ€™re said to have an obstructive lung disease, defined as an exhalation that is slower and shallower than that of a healthy person.1
The following list includes examples of obstructive lung diseases in which FVC is typically decreased:
Restrictive lung diseases are also characterized by a decrease in FVC, but because this measurement is reduced in both obstructive and restrictive lung disorders, measuring FVC alone cannot diagnose lung disease. To confirm a true restriction, total lung capacity (TLC) is required.1
TLC is defined as an inhalation that is far less than would be expected in a healthy person. TLC represents the amount of air present lungs in the lungs after taking the deepest breath possible.1
Restrictive lung diseases are further categorized as intrinsic, extrinsic and neurological. Lung diseases that have a restrictive pattern are listed below, separated by category:
Intrinsic restrictive disorders occur as a result of the lungs, themselves, such as in the following:
Extrinsic restrictive disorders occur as a result of something outside the lungs as per the examples below:
Neurological restrictive disorders are caused by disorders of the central nervous system and include the following:
 Johnson, Jeremy D., MD, MPH & Theurer, Wesley M., DO, MPH. A Stepwise Approach to the Interpretation of Pulmonary Function Test. Am Fam Physician.Â 2014Â MarÂ 1;89(5):359-366.
 WebMD. Forced Expiratory Volume and Forced Vital Capacity â€“ Topic Overview. Accessed March 17, 2018.
 Prohealth Insight. Types and Causes of Restrictive Lung Diseases. Accessed March 17, 2018.