Spirometry is the best test to assess lung function. It often is used to evaluate a person who has a chronic cough and sputum (mucus) production and a history of risk factors for chronic obstructive pulmonary disease (COPD) or Asthma, even if shortness of breath is not present. It is also used to find out whether a specific therapy has improved lung function or whether your lung disease is getting worse.

During the test:

• A tube is connected to the spirometer.
• You place your mouth on the tube and take the deepest breath possible.
• You then blow out as hard and as fast as possible.

This should be repeated several times during the visit to ensure accurate results.

This test measures the flow and amount of air when you breathe in and out as deeply and forcefully as you can.

The test is divided into:

• Forced expiratory volume in 1 second (FEV1), the amount of air breathed out as forcefully as possible in 1 second. The FEV1 value helps to estimate the severity of the illness.
• Forced vital capacity (FVC), the amount of air that can be forcibly breathed out after taking a deep breath.

The normal values for each of the measurements depend on your age, height, gender, and race. This is known as the predicted value. A reduction in the ratio of FEV1 to the FVC points to airway obstruction, including COPD and asthma.

These measurements us to diagnose airway diseases and find out the severity of the disease.