Pulmonary function tests are a group of tests that measure how well the lungs take in and release air and how well they move gases such as oxygen from the atmosphere into the body’s circulation.

Pulmonary function tests are done to:

• Diagnose certain types of lung disease (most commonly asthma, chronic bronchitis and emphysema)
• Help find the cause of shortness of breath
• Assess the effect of medication to treat your lung disease
• Assess the effect of medication prescribed to treat your lung disease
• Assess the effect of medication that may negatively affect your lung function (for example, amiodarone)
• Measure progress in disease progression
• To assess perioperative pulmonary risk prior to undergoing surgery

The most commonly performed test is called “spirometry.” With this test you will breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer records the amount and the rate of air that you breathe in and out over a period of time. For some of the test measurements, you can breathe normally and quietly. Other tests require forced inhalation or exhalation after a deep breath. You will be asked to wear a nose clip so we can collect all the air that comes out of your mouth. “Lung volume” is measured in other ways. In one way you will be asked to sit in a sealed, clear box that looks like a telephone booth (body plethysmograph) while breathing in and out into a mouthpiece. Changes in pressure inside the box help determine the lung volume.

Lung volume can also be measured when you breathe nitrogen or helium gas through a tube for a certain period of time. For one test known as a “methacholine challenge test” you will have to breathe in medication before the test.

Do not eat a heavy meal before the test. Do not smoke for 4 – 6 hours before the test. You’ll get specific instructions if you need to stop using bronchodilators or inhaler medications prior to the test. The tests are usually very well tolerated. Since the test involves some forced and rapid breathing, you may have some temporary shortness of breath or light-headedness.