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Your Guide to Lung Diseases.
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About.com Health's Disease and Condition content is reviewed by Sanja Jelic, MD

Pulmonary function tests are diagnostic tests used for measuring how well the lungs take in air and expel air, and how efficiently they exchange oxygen and carbon dioxide with the blood.

Pulmonary function tests include the following:

Spirometry

This test measures how well the lungs are able to exhale carbon dioxide.

Lung Volume Measurement

This testing is effective in diagnosing restrictive lung diseases. Restrictive lung diseases inhibit a person's ability to inhale a sufficient volume of air. Restrictive lung diseases are caused by inflammation or scarring of the lung tissue or by chest wall abnormalities.

Body Plethsmography is the most accurate way of determining lung volume measurement. A person sits in a sealed, transparent box for the testing. As the patient breathes in and out through a mouthpiece, the pressure inside the box is measured and evaluated.

Another way lung volume can be measured is by breathing nitrogen or helium gas through a tube for a specified period of time. The gas concentration in the chamber is measured to determine the lung volume.

Diffusion Capacity

This testing measures how rapidly gas travels from the lungs to the blood. A person briefly breathes carbon monoxide, then the carbon monoxide in the person's exhaled air is measured.