Lung Function Tests
Lung function tests (also called pulmonary function tests, or PFTs) evaluate how well your lungs work. The tests determine how much air your lungs can hold and how quickly you can move air in and out of your lungs. The tests can diagnose lung diseases, measure the severity of lung problems and check to see how well treatment for a lung disease is working.
Other tests such as respiratory muscle strength assessment and cough peak flow may also be done to determine lung function.
Spirometry
Spirometry is the first lung function test done. It measures how much and how quickly you can move air out of your lungs. For this test, you breathe into a mouthpiece attached to a recording device (spirometer). The information collected by the spirometer may be printed out on a chart called a spirogram.
The common lung function values measured with spirometry are:
- Forced vital capacity (FVC). This measures the amount of air you can exhale with force after you inhale as deeply as possible.
- Forced expiratory volume (FEV). This measures the amount of air you can exhale with force in one breath. The amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3). FEV1 divided by FVC can also be determined.
- Peak expiratory flow (PEF). This measures how quickly you can exhale. It is usually measured at the same time as your forced vital capacity (FVC).
- Maximum voluntary ventilation (MVV). This measures the greatest amount of air you can breathe in and out during one minute.
- Slow vital capacity (SVC). This measures the amount of air you can slowly exhale after you inhale as deeply as possible.
- Total lung capacity (TLC). This measures the amount of air in your lungs after you inhale as deeply as possible.
Respiratory Muscle Strength
Respiratory muscle strength can be assessed noninvasively by determinations of respiratory muscle pressures.
Maximal inspiratory mouth pressure (PImax): Patients breathe through a flanged mouthpiece with nose clips in place. Patients are instructed to first exhale and then inhale as forcefully as possible.
Maximal expiratory mouth pressure (PEmax): Patients breathe through a flanged mouthpiece with nose clips in place. Patients are instructed to first inhale and then exhale as forcefully as possible.
Sniff nasal-inspiratory force (SNIF): A polyethylene catheter ending in a plug is attached to a pressure transducer, and the plug end is inserted into a nostril. The contralateral nostril is occluded, and the patient is instructed to first exhale, then close the mouth and take a deep sniff or a maximal inspiratory effort.
Cough peak flow measures the peak flow during voluntary maximal cough. To measure the cough peak flow, the sitting subjects are instructed to take a full inspiration and to cough into the face mask connected to a peak flowmeter as forcefully as possible.
How To Prepare for Lung Function Tests
Do not eat a heavy meal just before this test because a full stomach may prevent your lungs from fully expanding. 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 contain caffeine because it can cause your airways to relax and allow more air than usual to pass through.
How Lung Function Tests Are 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.
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 30 to 60 minutes, depending upon how many tests are done.
How It Feels
You may cough or feel lightheaded after breathing in or out rapidly, but you will be given a chance to rest between tests. You may find it uncomfortable to wear the nose clip. Breathing through the mouthpiece for a long period of time may be uncomfortable.
Risks
Lung function tests present little or no risk.
Rev. 12/07
