Pulmonary (lung) function tests (PFT's) are tests used in the diagnosis of lung disease. These tests can often identify problems early in the course of disease, sometimes before physical examinations or chest X-rays.

Although Pulmonary Function Testing may not be able to determine the cause of an abnormality, it can be used in combination with other tests to help determine what type of lung disease a person has.

How Your Lungs Work
The main job of your lungs is to bring oxygen into your body and get rid of carbon dioxide in your blood. When you breathe, your lungs and chest wall act as a bellows to bring in fresh air. The upper airway carries air to the lungs. The lower airways branch out like a tree, ending in air sacs called alveoli. These alveoli pass oxygen to your blood stream while at the same time they collect waste gases from your blood such as carbon dioxide. These waste products are then returned to the lungs and released when you exhale out. If your lungs are exposed for long periods to too many pollutants such as dust, smoke or chemical fumes, the lungs defense mechanism may become overloaded and get worn out. Healthy lung tissue is elastic, expanding and contracting with each breath. Some lung diseases interfere with the lungs' elastic property and make the lungs "stiff." Stiff lungs often cause the lung volume to be reduced, which is called lung restriction. Other diseases may cause an obstruction in the airway, narrowing the tubes of the lung.

Testing of your lungs
The basic test of mechanical lung function can be done with a spirometer. (A spirometer is an instrument used to measure the volume of air entering and leaving the lungs.) To do the test, a person inhales fully and then blows out the air in his or her lungs through a tube as hard, fast and completely as possible. The test is repeated until at least two of the exhaled breaths are as good as possible. The spirometer measures the amount of air expelled and the speed at which the lungs can be emptied. These measurements are useful in evaluating respiratory disease. These measurements are called FVC and FEV1, and are described below. Forced Vital Capacity (FVC) is the maximum volume of air that can be blown out at maximum speed after a full breath is taken. AN FVC between 80% and 120% of the predicted level is considered normal. When lungs are stiff because of diseases of the lung tissue, such as pneumonia or lung scarring due to asbestos exposure, they often show reduced lung volume. When a disease causes this type of abnormality, it is called a restrictive lung disease. A normal FVC means its is unlikely that a person has a restrictive lung disease. The FVC can be low for other reasons, such as chest pain, other types of illness or lack of effort. Forced Expiratory Volume in One Second (FEV1) is the maximum volume of air that can be exhaled during the first second of a complete, fast, forced expiration. An FEV1 between 80% and 120% of the predicted level is considered normal. FEV1 is useful in diagnosing obstructive lung disease. FEV1 is reduced when the airways (bronchial tubes) are narrowed or obstructed, as in asthma. It can also be reduced in restrictive lung disease. Ratio of FEV1\FVC - The ratio of the two values is useful in determining the type of lung disease a person may have. A ratio of 0.7 or above is considered normal. The ratio of FEV1 to FVC may be reduced in the presence of airway obstruction, but the ratio is normal in restrictive lung disease.

Spirometry testing is useful for determining
1) if a person has lung disease
2) what type it is
3) whether a person is getting better or worse
4) how impaired a person's health is.

How Are Tests Interpreted?
An individual's lung function test results are interpreted by comparing them to the results predicted for a person of the same sex, age, height and race. This simple exam is a valuable tool in a full program for detecting and preventing serious lung disease. Symptoms of lung disease such as shortness of breath, wheezing and coughing usually develop gradually. Lung function tests and an awareness of pulmonary symptoms are useful in early detection of lung disease. PFTs can help detect illness at an early stage before symptoms are apparent.