What is Total Lung Capacity?

A Measurement Used In Chronic Obstructive Pulmonary Disease (COPD)

Doctor checking lung of mature patient
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Total lung capacity, or TLC, refers to the total amount of air in the lungs after taking the deepest breath possible.

Patients with chronic obstructive pulmonary disease (COPD) are often unable to exhale fully, resulting in hyperinflation of the lungs and a greater total lung capacity.

How is Total Lung Capacity Tested?

TLC is measured through body plethysmography, one of many pulmonary function tests that help to determine how much air is present in your lungs when you take a deep breath and how much air is left in your lungs after you exhale as much as you can.

 Body plethysmography helps your doctor to know more about your lung disease and how to treat it.

Measured in milliliters, the maximum capacity of a healthy lung is approximately 6,000 mL. In patients with COPD, the amount of air left in the lungs during the breathing process is more than normal, a condition known as hyperinflation. 

Spirometry is the lung test usually used to diagnose COPD, but - unlike body plethysmography - it does not on it's own provide information on total lung capacity or lung residual volume. Together, these tests can give your doctor a more complete picture of your condition. 

Lung Hyperinflation In COPD

Hyperinflation, which can occur with exercise or even everyday activity, causes shortness or breath. This may cause some people with COPD to avoid physical activity, to become physically deconditioned, to have a lower quality of life and to have an elevated risk of other illnesses, such as cardiovascular disease.


Why Is Total Lung Capacity Tested?

Total lung capacity is typically tested to diagnose and evaluate restrictive and obstructive lung diseases. In addition, your doctor may order body plethysmograph to test your response to different treatments, such as bronchodilators, methacholine, histamine or isocapnic hyperventilation.

You should not undergo body plethysmograph if you are mentally confused, have poor muscle control or parkinsonism or are on continuous oxygen support that cannot be stopped even temporarily.

How is Body Plethysmography Performed?

If your doctor orders a body plethysmography test to measure your total lung capacity, you can take comfort in knowing this test is relatively simple and painless.

During the test, you will sit in a clear glass booth roughly the size of a phone booth and then, wearing a nose clip, you will be instructed by a respiratory therapist to breathe through a mouthpiece and tube attached to the testing machine. Sometimes, a tracer gas such as carbon dioxide, is included in the air coming from the machine.

The test typically takes about three minutes. It measures changes in air pressure inside the booth to determine how much air you can breathe into your lungs.

To get the most accurate results, prior to the test you should not:

  • smoke for at least one hour
  • drink alcohol for at least four hours
  • exercise within 30 minutes
  • eat a large meal within two hours

Your doctor may also instruct you to not take certain medications on the day of the test. Be sure to follow your doctor's instructions precisely.


Body Plethysmography (Pulmonary Function Test). Cleveland Clinic. Updated May 9, 2014. 

Pulmonary function tests. National Institutes of Health. Updated December 3, 2013. 

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