What they are

Lung (or pulmonary) function tests test how efficiently you are breathing. You will be asked to put on a nose-clip so that all your breathing takes place through the mouth, then will breath into a mouthpiece attached to a machine that measures the air you breath in and out.

Different tests may be required for different reasons; for example, in some tests you will be asked to take as deep a breath as possible then exhale as fully as possible to measure your Forced Vital Capacity (FVC); or you may be asked to breath in and out rapidly for a period.

Sometimes you may be asked to breath in a spray drug first, to expand the airways in your lungs, or you may be asked to breath in a special mix of oxygen and carbon dioxide to see how well your lungs are absorbing the oxygen and excreting the carbon dioxide.

How they will help

Lung function tests are used to help determine the cause of shortness of breath and other breathing difficulties. They can help to differentiate between different forms of respiratory disease, such as obstructive conditions like asthma or problems caused by infections such as PCP.