Lung Function Test

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 add oxygen and remove carbon dioxide from your blood. The tests can diagnose lung diseases and measure the severity of lung problems.

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.
  • Residual volume (RV). This measures the amount of air in your lungs after you exhale with force.
  • 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).

Why It Is Done

Lung function tests are done to:

  • Determine the cause of breathing problems.
  • Diagnose certain lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD).
  • Evaluate a person's lung function before surgery.
  • Monitor the lung function of a person who is regularly exposed to substances such as asbestos or radon that can damage the lungs.
  • Monitor the effectiveness of treatment for lung diseases.

How To Prepare

Tell your doctor if you:

  • Have had recent chest pains or a heart attack.
  • Take medication for a lung problem, such as asthma. You may need to stop taking some medications before testing.
  • Are allergic to any medications.

Do not eat a heavy meal just before this test because a full stomach may prevent your lungs from fully expanding. You should not smoke or exercise strenuously for 6 hours before the test. On the day of the test, wear loose clothing that does not restrict your breathing in any way.

If you have dentures, wear them during the test to help you form a tight seal around the mouthpiece of the spirometer.

Risks

Lung function tests present little or no risk to a healthy person. If you have a serious heart or lung condition, discuss your risks with your doctor.