Lung Function Breathing Tests

What are lung function breathing tests?

Special breathing tests play a key role in finding out if a person has chronic obstructive pulmonary disease (COPD). These tests can also be used to find out the stage of a person’s COPD. Lung function tests are used to measure how well a person’s lungs are working. People with COPD have lungs that do not function as well as they should, so these tests give healthcare providers the information they need to diagnose and treat COPD.

Healthcare providers often use these types of lung function breathing tests:

  • Spirometry
  • Lung volume measurement
  • Lung diffusion capacity

What do lung function tests show about a person’s breathing?1

The lung function tests provide different kinds of information about how a person breathes:

  • The largest amount of air the person can breathe in (this is called “inhaling”)
  • The largest amount of air the person can breathe out (this is called “exhaling”)
  • How fast the person can exhale
  • How much oxygen the person’s lungs can absorb when inhaling
  • How much carbon dioxide the person’s lungs can remove when exhaling

What is a spirometry test?1,2

Spirometry plays a very important role in diagnosing and managing COPD. It is the main way that healthcare providers can know for sure that a person has the disease. Spirometry measurements also show the stage of a person’s COPD, and whether or not the disease has gotten worse.

A spirometry test measures how well the lungs are working while exhaling. It is a simple test that shows how much air a person can exhale at once, and how quickly the air moves out of the lungs.

The tests are done using a machine called a “spirometer.” There is a small mouthpiece attached to the machine to measure the patient’s breathing. The mouthpiece fits into the patient’s mouth. Small clips are attached to the nostrils to make sure all the air goes out through the mouthpiece.

During the test, the patient is asked to take the deepest breath in and then to exhale as hard as possible. A sensor in the machine measures the amount and the speed of the air that is exhaled.

The results of the spirometry test will show if the air flowing out of the person’s lungs is blocked by COPD or some other kind of respiratory problem. If the person does have COPD, the results can help figure out what stage of COPD it is.

What is a lung volume measurement?1

The lung volume measurement test is another test of the amount of air a person can breathe in and out. It measures two amounts:

  • The largest amount of air a person’s lungs can take in while inhaling
  • How much air is still in the lungs after fully exhaling

During the test, the patient sits inside of a glass booth and breathes in and out into a tube. The air pressure inside of the booth changes during breathing, which shows amount of air in the person’s lungs after inhaling and exhaling.

What is a lung diffusion capacity test?3

Two key functions of the lungs are:

  • To absorb oxygen into the bloodstream from the air we inhale
  • To remove carbon dioxide from the bloodstream and into the air we exhale

A lung diffusion capacity test measures how well the lungs are able to do both of these jobs. During the test, a mouthpiece is used to deliver a very tiny amount of harmless gas into the patient’s lungs. The patient is asked to hold in the breath for 10 seconds, and then exhale as quickly as possible.

The exhaled air is tested to show how well the lungs are absorbing oxygen and removing carbon dioxide. The results of the test can help show whether a person has COPD. Lung damage from COPD can prevent the lungs from exchanging as much oxygen and carbon dioxide as the body needs to function well. It can also show whether a person has other respiratory problems that affect blood flow in the lungs, such as pulmonary hypertension.

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Written by: Anna Nicholson | Last reviewed: July 2015.