Skip to content

Lung Disease & Respiratory Health Center

Font Size

Lung Function Tests

Gas diffusion tests measure the amount of oxygen and other gases camera.gif that cross the lungs' air sacs (alveoli camera.gif) 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 diffusion capacity (also called DLCO), 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

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.

1 | 2 | 3 | 4 | 5 | 6 | 7

WebMD Medical Reference from Healthwise

Last Updated: /2, 14 1
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.

Today on WebMD

man coughing
You may not even know you have it.
blood clot
Signs of this potentially fatal complication.
man coughing
When a cold becomes bronchitis.
human lungs
Causes behind painful breathing, fluid buildup.

chest x-ray
Bronchitis Overview
Copd Myth Fact Quiz
Energy Boosting Foods

woman coughing
Lung xray and caduceus