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Lung volumes are studies that measure the amount of air inhaled, exhaled or present within the lungs during different phases of breathing. They provide an indication of lung function and capacity, and are necessary for identifying, quantifying and characterizing the severity of various lung diseases. It also helps determine the extent of disability, course of the disease and response to therapy.
The lung volumes usually measured include:
- Tidal volume: The amount of air inhaled and exhaled during normal breathing. Normally this is about 500 mL.
- Inspiratory reserve volume: Additional air that can be forcibly inhaled after normal inhalation.
- Expiratory reserve volume: Additional air that can be forcibly exhaled after normal exhalation.
- Residual volume: Air left in the lungs after maximum exhalation.
Lung volumes are measured with a spirometer. The device consists of a mouthpiece and tube attached to a machine. You are instructed to breathe orally through the mouthpiece in a particular manner. Soft clips are used to close your nostrils during the procedure. The test may be repeated three times for consistency. The entire procedure usually takes about 15 minutes and the results are displayed on a graph called a spirogram.