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Lung Function Tests

Body plethysmography may be used to measure:

  • Total lung capacity (TLC), which is the total amount of air your lungs can hold. For this test, you sit inside a small airtight room called a plethysmograph booth and breathe through a mouthpiece while pressure and air flow measurements are collected.
  • Residual volume (RV), which is the amount of air that remains in your lungs after you exhale as completely as possible. For this test, you sit inside the plethysmograph booth and breathe while the pressure of the booth is monitored. You may need to breathe through a mouthpiece while you are in the booth.

Inhalation challenge tests

Inhalation challenge tests are done to measure the response of your airways to substances that may be causing asthma or wheezing. These tests are also called provocation studies.

During inhalation testing, increasing amounts of a substance are inhaled through a nebulizer, a device that uses a face mask or mouthpiece to deliver the substance in a fine mist (aerosol). Sometimes, increasing amounts of methacholine or mannitol may be inhaled through the nebulizer. Spirometry readings are taken to evaluate lung function before, during, and after inhaling the substance.

In rare cases, a bronchospasm can occur with inhalation challenge testing. You will be closely monitored during and after the test.

Exercise stress tests

Exercise stress tests evaluate the effect of exercise on lung function tests. Spirometry readings are done after exercise and then again at rest.

Multiple-breath washout test

The multiple-breath washout test is done to check lung function in people with cystic fibrosis. For this test, you breathe air that contains a tracer gas through a tube. Then you breathe regular air while the amount of tracer gas you exhale is monitored. Test results are reported as a lung clearance index (LCI). A high LCI value means that the lungs are not working well.

Lung function results are measured directly in some tests and are calculated in others. No single test can determine all of the lung function values, so more than one type of test may be done. Some of the tests may be repeated after you inhale medicine that enlarges your airways (bronchodilator).

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.
  • Check the lung function of a person who is regularly exposed to substances that can damage the lungs.
  • Check 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 medicine for a lung problem such as asthma. You may need to stop taking some medicines before testing.
  • Are allergic to any medicines.
  • Have had recent surgery on your eyes, chest, or abdomen, or if you have had a collapsed lung (pneumothorax).

WebMD Medical Reference from Healthwise

Last Updated: April 25, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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