Pulmonary Function Tests

Pulmonary function tests measure how your lungs work. They measure airflow through the lungs, how much air the lungs can take in and how quickly oxygen gets into the blood. These may show symptoms of lung disease, how well treatment is working and how well the body is responding to treatment.

The pulmonary function tests that may be done when a person is being evaluated for a lung or a heart-lung transplant include:

  • Spirograms, which measure airflow. They are used to see if a patient has diseases such as asthma that block the flow of air inside the lungs. This test is done by having the patient blow into a testing device as rapidly and hard as possible for as long as possible. This is done twice to get an accurate measurement. If the test comes out abnormal, it may be done again using a medicine to open up the air passages of the lungs. If there is improvement in the measure, the patient may benefit from more medicine rather than lung transplantation.
  • Lung volume test, which measures how much air the lung can hold. The patient breathes a special mixture of gases at a normal rate for about three minutes. Then he or she slowly exhales. Using the measurements gained from the test and mathematical formulas, the doctor can estimate the amount of gas the lung can hold. If the measurement shows that lung volume is low, the patient may have a disease such as pulmonary fibrosis that interferes with the lung's ability to fill.
  • Diffusion capacity, which measures the body's ability to take oxygen from the lungs. In this test, the patient exhales as completely as possible. Then he or she breathes in a special mixture of gases and holds the breath for about 10 seconds. The breath that is exhaled is collected in an airtight bag for analysis. One of the gases in the mixture is one that quickly moves from the airways of the lungs into the blood. The amount of the gas that remains in the bag, tells the doctor how well the blood is picking up the gas from the lungs. A person who has a low diffusion capacity may have advanced emphysema or pulmonary fibrosis.
  • Ventilation perfusion scan, which compares the function of the right and left lungs. In this test, the patient is given a shot of a small amount of radioactive material. He or she is then asked to put on a face mask and breath in a radioactive gas, which spreads throughout the lungs. The gas is then exhaled normally. The radioactivity makes it easier for the doctors to see the flow of blood and gas throughout the lungs. It is normal to have less flow in the left lung because it is smaller. The test takes about an hour. Don't eat before taking the test.