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