Patient Education - Lung Cancer Program at UCLA
yourself about lung cancer:
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
- In a spirometry test, a person breathes into mouthpiece that is connected to
an instrument called a spirometer. The spirometer records the amount and the rate
of air that is breathed in and out over a specified time. Some of the test measurements
are obtained by normal, quiet breathing, and other tests require forced inhalation
or exhalation after a deep breath.
- Lung volume measurement can be performed in two ways. The most accurate way
is for a person to sit in a body plethysmograph, a sealed, transparent box that resembles
a telephone booth, while breathing in and out against into a mouthpiece. Changes
in pressure inside the box allow determination of the lung volume. Lung volume can
also be measured when a person breathes nitrogen or helium gas through a tube for
a specified period of time. The concentration of the gas in a chamber attached to
the tube is measured, allowing estimation of the lung volume.
- The diffusion capacity is measured when a person breathes carbon monoxide for
a very short time, often one breath. The concentration of carbon monoxide in exhaled
air is then measured. The difference in the amount of carbon monoxide inhaled and
the amount exhaled allows estimation of how rapidly gas can travel from the lungs
into the blood.
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.
Review Date: 2/27/2006
Reviewed By: David A. Kaufman, M.D., Assistant Professor, Division of Pulmonary,
Critical Care & Sleep Medicine, Mount Sinai School of Medicine, New York, NY.
Review provided by VeriMed Healthcare Network.
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