Pulmonary Function Tests

Pulmonary Function Tests are a broad range of tests that 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 disease, a person cannot inhale a normal volume of air. Restrictive lung diseases may be caused by inflammation or scaring of the long tissue (interstitial lung disease) or by abnormalities of the muscles or skeleton of the chest wall.

Testing the diffusion capacity permits an estimate of how efficiently the lungs transfer oxygen from the air into the bloodstream.


· Spirometry test: A person breathes into mouth piece 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.

· The diffusion capacity is measured when a person breathes carbon monoxide for a very short time, in one breath. The concentration of carbon monoxide in exhaled air is then measured. The differences in the amount of carbon monoxide inhaled and then exhaled allows estimation of how rapidly gas can travel from the lungs into the blood.

Preparation for the test:

· Do not eat a heavy meal before the test.
· Do not drink coffee or caffine containing beverages 4 to 6 hours before the test.
· Do not smoke for 4 to 6 hours prior to the test.
· Bronchodilators or inhaler medications should be withheld 4 to 6 hourse before the test.

To Diagnose certain types of lung diseases like asthma, bronchitis and emphysema, to determine the cause of shortness of breath, or to measure whether occupational exposure to contaminants affects lung function. It is done after the administration of medications to assess their effect, and to measure progress in disease treatment.

Normal Values:
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.
Abnormal results usually mean that a degree of chest or lung disease may be present.