Ratio of FEV1/FVC in Spirometry

In diagnosing and treating obstructive lung diseases such as chronic obstructive pulmonary disease (COPD), doctors often use various tests to determine the severity of the disease. One of these is a test called a spirometry, in which various measurements of lung function can be calculated.

One important measurement doctors use to monitor lung function is the ratio of forced expiratory volume in one second (FEV1) over forced vital capacity (FVC), also known as the Tiffeneau-Pinelli index. This is a measurement of the amount of air exhaled forcefully in one second compared to the full amount of air that can be forcefully exhaled in a complete breath.

The amount of air you exhale in one second is recorded as well at the total amount of air you are able to exhale. Based on the number of FVC calculated for your age and size, the ratio of these 2 values is then evaluated. Ordinarily, the two values are proportional. If the FVC is decreased, then the ratio is looked at more closely.

If your FVC is decreased but the ratio of FEV1/FVC is normal, this indicates a restrictive pattern. 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 effusion, which 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.

If your FVC is decreased and your FEV1/FVC ratio is also decreased, this is consistent with an obstructive form of lung diseases such as asthma and COPD. Usually, this diagnosis is reached if the FEV1/FVC is less than or equal to 70 to 80 percent of adults, and 85 percent in children. Damage to the airways and/or constriction of the airways is indicative of conditions such as:

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

If a restrictive pattern is observed, doctors will usually recommend full pulmonary function tests to further characterize your lung disease. If an obstructive pattern is found, the next step is usually to recommend treatment with a bronchodilator, a medication which helps to reduce constriction of the airways and repeating the test.

If you are being treated for obstructive lung disease, your doctor will most likely monitor your progress using your FEV1/FVC ratio. If the ratio improves with a bronchodilator, that 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, such as in COPD.