What does a spirometer measure?

Spirometry (meaning the measuring of breath) is the most common of the lung function tests. The spirometry test is performed using a device called a spirometer, which comes in several different varieties. It measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled by the lungs. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease (COPD). It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time.

Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible, preferably at least 6 seconds. It is sometimes directly followed by a rapid inspiration, (inhalation) in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor,.

During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of germs.