Lung Disease & Respiratory Health Center

How To Prepare continued...

Do not eat a heavy meal just before this test because a full stomach may prevent your lungs from fully expanding. You should not smoke or exercise vigorously for 6 hours before the test. On the day of the test, wear loose clothing that does not restrict your breathing in any way. You should also avoid food or drinks that have caffeine because it can cause your airways to relax and allow more air than usual to pass through.

If you have dentures, wear them during the test to help you form a tight seal around the mouthpiece of the spirometer.

How It Is Done

Lung function tests are usually done in special exam rooms that have all of the lung function measuring devices. The test is usually done by a specially trained respiratory therapist or technician. For most of the lung function tests, you will wear a nose clip to make sure that no air passes in or out of your nose during the test. You then will be asked to breathe into a mouthpiece connected to a recording device.

The exact procedure is different for each type of test. For example, you may be asked to inhale as deeply as possible and then to exhale as fast and as hard as possible. You also may be asked to breathe in and out as deeply and rapidly as possible for 15 seconds. Some tests may be repeated after you have inhaled a spray containing medicine that expands the airways in your lungs (bronchodilator). You may be asked to breathe a special mixture of gases, such as 100% oxygen, a mixture of helium and air, or a mixture of carbon monoxide and air. Sometimes a sample of blood may be taken from an artery in your wrist to measure blood gases.

If you have body plethysmography, you will be asked to sit inside a small enclosure similar to a telephone booth, with windows that allow you to see out. The booth measures small changes in pressure that occur as you breathe.

The accuracy of the tests depends on your ability to follow all of the instructions. The therapist may strongly encourage you to breathe deeply during some of the tests to get the best results.

The testing may take from 5 to 30 minutes, depending upon how many tests are done.