Ration of FEV1/FVC in Spirometry

Differentiating Ostructive and Restrictive Lung Diseases with FEV1FVC

What is the FEV1/FVC ratio and how does it help define lung diseases?. Istockphoto.com/Stock Photo©Gary518

Definition: FEV1/FVC

The ration FEV1/FVC is a ratio of the amount of air exhaled forcefully in one second over the amount of air that can be forcefully exhaled with a complete breath over how long it takes. The letters stand for forced expiratory volume in one second (FEV1) over forced vital capacity (FVC.)

Measuring FEV1/FVC

The ration of FEV1/FVC is measured during a test called a spirometry.  In this test a mask is placed over your face.

Measurement than are taken as you take in a deep breath and exhale as forcefully as possible.  The amount of air you exhale in one second is recorded as well at the total amount of air you are able to exhale.

Forced Vital Capacity (FVC)

The number for FVC is calculated by looking at what your FVC is predicted to be based on your age, your height, and your weight.

FEV1/FVC Ratio

Based on the number of FVC calculated for your age and size, the ratio of these 2 values is then evaluated.  Ordinarily, the 2 values are proportional. If the FVC is decreased, then the ratio is looked at more closely.

Decreased FVC with Proportional FEV1/FVC Ratio - Restrictive Pattern

If your FVC is decreased but the ratio of FEV1/FVC is normal, this indicates a restrictive pattern.  Restrictive lung diseases tend to be those in which the lung tissue itself is diseased (or other conditions) rather than constriction of the airways.

Decreased FVC with Decreased FEV1/FVC Ratio - Obstructive Pattern

If your FVC is decreased and your FEV1/FVC ratio are also decreased, this is consistent with an obstructive form of lung disease.  Usually, the criteria is that FEV1/FVC is less than or equal to 70 to 80% in adults, and 85% in children.

Next Steps

If a restrictive pattern is seen with this test, usually full pulmonary function tests will be recommended to further characterize your lung disease.

If an obstructive pattern is seen, the next step is usually treating the patient with a bronchodilator, a medication which helps to reduce constriction of the airways and repeating the test. There are two ways this can go. If the ratio improves with a bronchodilator it means that the obstruction is at least partially "reversible."  This is seen with conditions such as asthma.  If the ratio does not improve with a bronchodilator it may be irreversible.  This type of pattern is seen with chronic obstructive disease (COPD.)

Obstructive vs Restrictive Lung Diseases

Based on readings, as noted above, the FEV1/FVC gives valuable information in determining the next steps for evaluating lung diseases.  What are some of the differences between obstructive and restrictive airway diseases and what are some examples of each?

Restrictive Lung Disease

Restrictive lung diseases may be those in which the lung tissue itself is damaged, or when structurally someone is unable to breathe as deeply as normal.

  Some examples include:

  • Pulmonary fibrosis - Such as idiopathic pulmonary fibrosis, a scarring of the lungs of uncertain cause.
  • Deformities of the chest such as scoliosis or chest wall scaring.
  • Lung cancer surgery, such as a lobectomy or pneumonectomy.
  • Infections and inflammatory diseases such as pneumonia, tuberculosis, sarcoidosis, silicosis, and asbestosis.
  • Neurological disorders such as ALS
  • Pleural effusions - That is, fluid in the area between the linings which surround the lungs.
  • Ascites - A fluid buildup in the abdomen due to liver disease or cancer in the abdomen can cause a restrictive pattern by limiting the ability to take a deep breath.

Obstructive Lung Disease

Damage to the airways or constriction of the airways are included in conditions such as:

  • Asthma.
  • Chronic obstructive pulmonary diseases such as chronic bronchitis, emphysema, and bronchiectasis
  • Bronchiolitis

Also Known As: FEV1%, %FEV1


Johnson, J., and W. Theurer. A Stepwise Approach to the Interpretation of Pulmonary Function Tests. American Family Physician. 2014. 89(5):359-366.

Godfrey, M., and M. Jankowich. The Vital Capacity Is Vital:Epidemiology and Clinical Significance of the Restrictive Spirometry Pattern. Chest. 2016. 149(1):238-251.

Koo, K., Yun, H., Byeong-Ho, J. et al. Relationship Between Forced Vital Capacity and Framingham Cardiovascular Risk Score Beyond the Presence of Metabolic Syndrome: The Fourth Korea National Health and Nutrition Examination Survey. Medicine. 2015. 94(47):e2089.

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