Pulmonary function tests (PFTs) are noninvasive tests that show how well the lungs are working. The tests measure lung volume, capacity, rates of flow, and gas exchange. This information can help your healthcare provider diagnose and decide the treatment of certain lung disorders.

There are 2 types of disorders that cause problems with air moving in and out of the lungs:

• Obstructive.This is when air has trouble flowing out of the lungs due to airway resistance. This causes a decreased flow of air.
• Restrictive.This is when the lung tissue and/or chest muscles can’t expand enough. This creates problems with air flow, mostly due to lower lung volumes.

PFT can be done with 2 methods. These 2 methods may be used together and perform different tests, depending on the information that your healthcare provider is looking for:

• Spirometry.A spirometer is a device with a mouthpiece hooked up to a small electronic machine.
• Plethysmography.You sit or stand inside an air-tight box that looks like a short, square telephone booth to do the tests.