Spirometry is the most common type of pulmonary function or breathing test. This test measures how much air you can breathe in and out of your lungs, as well as how easily and fast you can the blow the air out of your lungs.

How is a pulmonary function test performed?

You sit in a clear airtight box that looks like a phone booth. The technologist asks you to breathe in and out of a mouthpiece. Changes in pressure inside the box help determine the lung volume. Lung volume can also be measured when you breathe nitrogen or helium gas through a tube for a certain period of time.

Why does a doctor order a pulmonary function test?

PFTs may be used to check lung function before surgery or other procedures in patients who have lung or heart problems, who are smokers, or who have other health conditions. Another use of PFTs is to assess treatment for asthma, emphysema, and other chronic lung problems.