Test: Lung Function Tests

Two tests are used to detect airflow problems in the lungs: spirometry, which measures how quickly the lungs fill and empty, and the lung volume test, which shows how much air the lungs can hold. These tests distinguish between disorders that narrow the airways and those that cause lung shrinkage. Gas transfer tests (not shown) use a small amount of inhaled carbon monoxide to determine how fast a gas is absorbed from the lungs into the blood.


A spirometer is used to measure the volume of air (in litres) that you can inhale and exhale over a period of time. The results show whether the airways are narrowed as a result of lung disorders such as asthma. Spirometry can also be used to monitor the effectiveness of certain treatments for lung disorders, such as bronchodilator drugs, which widen the airways.

Using the spirometer

You will be asked to inhale and exhale fully through a mouthpiece several times. The volume of air inhaled and exhaled is displayed on the monitor.


Spirometry graph

This graph shows the effect of drug treatment to widen the air passages in a person with asthma. The volume of air that is exhaled in 1 second rises from about 1 litre to 2 litres soon after the drugs have been taken.

Lung volume test

This test measures the volume of air (in litres) that can be taken in with a full breath and the volume of air that remains in the lungs when the breath is fully exhaled. The lung volume test is used to help diagnose disorders such as chronic obstructive pulmonary disease that affect the volume of air retained by the lungs after breathing out.

During the test

You will be asked to sit in an airtight booth and breathe in and out through a tube as fully as you can. The volume of air you can inhale and exhale is displayed as a graph on a monitor.


Lung volume graph

This shows the amount of air exhaled and inhaled by normally functioning lungs.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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