Lung Function Tests
Lung function tests (also called pulmonary function tests, or PFTs) check how well your lungs work. The tests determine how much air your lungs can hold, how quickly you can move air in and out of your lungs, and how well your lungs put oxygen into and remove carbon dioxide from your blood. 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.
Spirometry is the first and most commonly done lung function test. 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 more common lung function values measured with spirometry are:
Gas diffusion tests
Gas diffusion tests measure the amount of oxygen and other gases that cross the lungs' air sacs (alveoli) per minute. These tests evaluate how well gases are being absorbed into your blood from your lungs. Gas diffusion tests include:
Body plethysmography may be used to measure:
Inhalation challenge tests
Inhalation challenge tests are done to measure the response of your airways to substances that may be causing asthma or wheezing. These tests are also called provocation studies.
During inhalation testing, increasing amounts of a substance are inhaled through a nebulizer, a device that uses a face mask or mouthpiece to deliver the substance in a fine mist (aerosol). Sometimes, increasing amounts of methacholine or mannitol may be inhaled through the nebulizer. Spirometry readings are taken to evaluate lung function before, during, and after inhaling the substance.
In rare cases, a bronchospasm can occur with inhalation challenge testing. You will be closely monitored during and after the test.
Exercise stress tests
Exercise stress tests evaluate the effect of exercise on lung function tests. Spirometry readings are done after exercise and then again at rest.
Multiple-breath washout test
The multiple-breath washout test is done to check lung function in people with cystic fibrosis. For this test, you breathe air that contains a tracer gas through a tube. Then you breathe regular air while the amount of tracer gas you exhale is monitored. Test results are reported as a lung clearance index (LCI). A high LCI value means that the lungs are not working well.
Lung function results are measured directly in some tests and are calculated in others. No single test can determine all of the lung function values, so more than one type of test may be done. Some of the tests may be repeated after you inhale medicine that enlarges your airways (bronchodilator).
Why It Is Done
Lung function tests are done to:
How To Prepare
Tell your doctor if you:
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.
How It Feels
If you have an arterial blood gas test, you may feel some pain from the needle used to collect the blood. The other lung function tests are usually painless. Some of the tests may be tiring for people who have a lung disease.
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.
If you have body plethysmography, you may feel uncomfortable in the airtight plethysmograph booth. But the therapist will be nearby during the test to open the door if you feel too uncomfortable.
If you are given breathing medicine, it may cause you to shake or may increase your heart rate. If you feel any chest pain or discomfort, tell the therapist right away.
Lung function tests present little or no risk to a healthy person. If you have a serious heart or lung condition, discuss your risks with your doctor.
Lung function tests (also called pulmonary function tests, or PFTs) check how well your lungs work. The normal value ranges for lung function tests will be adjusted for your age, height, sex, and sometimes weight and race. Results are often expressed in terms of a percentage of the expected value. Most test results are available right away.
Test results are within the normal ranges for a person with healthy lungs.
Test results are outside of the normal range for a person with healthy lungs. This may mean that some kind of lung disease is present. There are two main types of lung disease that can be found with lung function tests: obstructive and restrictive.
In obstructive lung conditions, the airways are narrowed, usually causing an increase in the time it takes to empty the lungs. Obstructive lung disease can be caused by conditions such as emphysema, bronchitis, infection (which produces inflammation), and asthma.
FEV1 often increases after using medicine that expands the airways in people with reversible obstructive disease like asthma.
In restrictive lung conditions, there is a loss of lung tissue, a decrease in the lungs' ability to expand, or a decrease in the lungs' ability to transfer oxygen to the blood (or carbon dioxide out of the blood). Restrictive lung disease can be caused by conditions such as pneumonia, lung cancer, scleroderma, pulmonary fibrosis, sarcoidosis, or multiple sclerosis. Other restrictive conditions include some chest injuries, being very overweight (obesity), pregnancy, and loss of lung tissue due to surgery.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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