Lung function tests (also called pulmonary function tests, or PFTs) evaluate how well your lungs work. The tests determine how much air your lungs can hold, how quickly you can move air in and out of your lungs, and how well your lungs put oxygen into and remove carbon dioxide from your blood. The tests can diagnose lung diseases, measure the severity of lung problems, and check to see how well treatment for a lung disease is working.

Other tests such as residual volume, gas diffusion tests, body plethysmography, inhalation challenge tests, and exercise stress tests may also be done to determine lung function.

Spirometry is the first lung function test done. It measures how much and how quickly you can move air out of your lungs. For this test, you breathe into a mouthpiece attached to a recording device (spirometer). The information collected by the spirometer may be printed out on a chart called a spirogram.

The more common lung function values measured with spirometry are:

• Forced vital capacity (FVC). This measures the amount of air you can exhale with force after you inhale as deeply as possible.
• Forced expiratory volume (FEV). This measures the amount of air you can exhale with force in one breath. The amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3). FEV1 divided by FVC can also be determined.
• Forced expiratory flow 25% to 75%. This measures the air flow halfway through an exhale (FVC).
• Peak expiratory flow (PEF). This measures how quickly you can exhale. It is usually measured at the same time as your forced vital capacity (FVC).
• Maximum voluntary ventilation (MVV). This measures the greatest amount of air you can breathe in and out during one minute.
• Slow vital capacity (SVC). This measures the amount of air you can slowly exhale after you inhale as deeply as possible.
• Total lung capacity (TLC). This measures the amount of air in your lungs after you inhale as deeply as possible.
• Functional residual capacity (FRC). This measures the amount of air in your lungs at the end of a normal exhaled breath.
• Expiratory reserve volume (ERV). This measures the difference between the amount of air in your lungs after a normal exhale (FRC) and the amount after you exhale with force (RV).

Gas diffusion tests

Gas diffusion tests measure the amount of oxygen and other gases that cross the lungs' air sacs (alveoli) per minute. These tests evaluate how well gases are being absorbed into your blood from your lungs. Gas diffusion tests include:

• Arterial blood gases, which determine the amount of oxygen and carbon dioxide in your bloodstream.
• Carbon monoxide diffusing capacity (also called transfer factor, or TF), which measures how well your lungs transfer a small amount of carbon monoxide (CO) into the blood. Two different methods are used for this test. If the single-breath or breath-holding method is used, you will take a breath of air containing a very small amount of carbon monoxide from a container while measurements are taken. In the steady-state method, you will breathe air containing a very small amount of carbon monoxide from a container. The amount of carbon monoxide in the breath you exhale is then measured. Diffusing capacity provides an estimate of how well a gas is able to move from your lungs into your blood.

Body plethysmography