Pulmonary Function Tests - Diagnosing Copd: Smoking Cessation

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Pulmonary function tests

These tests can help determine whether you have COPD and, if so, how severe it is. The tests use a spirometer, a machine that measures how much air you can hold in your lungs and how easily you can inhale and exhale. Pulmonary function tests are done either in the doctor's office or at a hospital. They are not invasive or uncomfortable — you simply inhale and exhale forcefully through an air tube attached to the spirometer. The spirometer then prints out a graph that shows two key values:

• Forced vital capacity (FVC) is the maximum volume of air you can exhale with force into the spirometer. The FVC, measured in liters, shows how large your lungs are, how elastic the lung tissue is, and how well your airways open and close.

• Forced expiratory volume in one second (FEV1) is the maximum volume of air exhaled in one second.

FVC and FEV1 are meaningful separately and in relation to each other. The percentage of FEV1 relative to FVC is the best clue to whether you have COPD, but the level of FEV1 itself is often the best indicator of how severe it is. Normally, FEV1 is about 70% of FVC, but with COPD, the result is often less than 60%, because it takes longer to exhale air through narrowed airways. To estimate the severity of your disease, the doctor compares the FEV1 reading against normal lung function based on your age, height, and sex. The less air you can exhale forcefully in relation to the normal standards for someone like you, the more severe the disease.

Last updated:	May 23, 2007