What should you know about spirometer vital capacity?

During the test, you inhale fully and then breathe out as far as you can through a mouthpiece. The device records the volume released. A result is interpreted alongside your age, height, sex, symptoms, examination and other readings, rather than in isolation.

A reduced vital capacity can occur when the lungs cannot expand fully, the chest wall limits movement, breathing muscles are weak, or the effort was incomplete. A single result does not identify one condition by itself.

Follow the testing centre's instructions about meals, smoking, exercise and medicines. Wear clothing that allows your chest and abdomen to move. Sit upright, seal your lips around the mouthpiece, and follow the technician's instructions closely. Several attempts may be needed so the most consistent effort can be assessed.

Contact a clinician promptly for new or worsening breathlessness, chest pain, blue or grey lips, fainting, confusion, or difficulty speaking because of shortness of breath. After testing, tell staff if you feel dizzy, wheezy or unusually unwell; they can pause the procedure and check you.

Ask which part of the result was reduced, whether the effort was technically acceptable, and how the finding fits with your symptoms. You can also ask whether repeat testing, bronchodilator testing or another lung assessment is appropriate.