Pulmonary function tests measure the volume and the rate of airflow of the lungs. A device with a mouthpiece is used. The tests are accurate only if the patient cooperates in breathing properly into the mouthpiece. Some of the tests require the patient to breathe normally. Others require the patient to breathe in as deeply and breathe out as completely as possible. The tests that take the most effort require exhaling into the mouthpiece as quickly and completely as possible. The machine records the patterns of these efforts. Some tests also include a strap around the chest to measure volume and pressure. From just a few tests, healthcare providers can determine more than a dozen lung measurements.

The purpose of these tests is to find the cause of breathing problems and to measure how severe these problems are. If you are going to have testing, your healthcare provider will ask you to eat only a light meal and not smoke for 4 to 6 hours. Your provider may instruct you to stop using asthma drugs for some period. The tests are painless and you can rest between tests. The technician conducting the tests will instruct you on breathing and encourage you during your efforts. Most of the tests are repeated 3 or more times. After the tests, you may resume normal diet, drugs and activities. Performing these tests may be risky for persons with severe or recent heart problems. Providers watch these patients carefully during and after the tests for any signs of distress. These tests are usually done in your provider's office or a specially equipped respiratory care center.

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