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You have been tested to see how well the gas exchange in your lungs is working.

You need lungs to breath. When we breathe in, oxygen enters the lungs and accumulates in the blood. This blood then flows to the heart. The heart then pumps the oxygen-rich blood throughout the body. All of the organs are supplied with oxygen as a result.

In the lungs, the airways branch out like a tree does, and they end in the alveoli. In the alveoli, oxygen is absorbed into the blood and carbon dioxide is released to be breathed out. The exchange of oxygen and carbon dioxide in the lungs is also known as the gas exchange.

For the examination, the patient usually inhales a particular gas through a mouthpiece and then holds in the air for a while. Part of the gas gets absorbed into the blood by the alveoli. The rest of the gas is exhaled again. The gas in the exhaled air is then measured. The values measured show how well the gas exchange in the lungs is working. If lung tissue is damaged, for example, less oxygen from the inhaled air may be getting into the blood.