Tests and studies: Lung function tests
Pulmonary function tests
Pulmonary function tests are a broad range of tests that are usually done in a health care provider's office or a specialized facility. They measure how well the lungs take in and exhale air and how efficiently they transfer oxygen into the blood.
Spirometry measures how well the lungs exhale. The information gathered during this test is useful in diagnosing certain types of lung disorders, but is most useful when assessing for obstructive lung diseases (especially asthma and chronic obstructive pulmonary disease, COPD).
Lung volume measurement detects restrictive lung diseases. In this set of diseases, a person cannot inhale a normal volume of air. Restrictive lung diseases may be caused by inflammation or scarring of the lung tissue (interstitial lung disease) or by abnormalities of the muscles or skeleton of the chest wall.
Testing the diffusion capacity (also called the DLCO) permits an estimate of how efficiently the lungs transfer oxygen from the air into the bloodstream.
PFTs; Spirometry; Spirogram; Lung function tests
How the Test is Performed
How to Prepare for the Test
Do not eat a heavy meal before the test. Do not smoke for 4 to 6 hours prior to the test. Specific instructions will be given if bronchodilators or inhaler medications should be withheld. Sometimes, medication may be inhaled prior to the test.
How the Test Will Feel
Since the test involves some forced breathing and rapid breathing, some temporary shortness of breath or lightheadedness may be experienced. There is a tight fitting mouth piece to breathe through, and nose clips are applied.
Why the Test is Performed
The test is performed to diagnose certain types of lung disease (especially asthma, bronchitis, and emphysema), to determine the cause of shortness of breath, or to measure whether occupational exposure to contaminants affects lung function. It can also be used after the administration of medications to assess their effect, and to measure progress in disease treatment.
Normal values are based upon the age, height, ethnicity, and sex of the person being tested. Normal results are expressed as a percentage. A value is usually considered abnormal if it is less than 80% of the predicted value for that person.
What Abnormal Results Mean
Abnormal results usually mean that a degree of chest or lung disease may be present.
The risk is minimal for most people. There is a small risk of collapsed lung in people with a certain type of lung disease. The test should not be given to a person who has experienced a recent heart attack, or who has certain other types of heart disease.
Cooperation from the patient performing the test is crucial in providing accurate results. A poor seal around the mouthpiece of the spirometer can give poor results that do not permit interpretation. Do not smoke before the test.