Pulmonary function test

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Pulmonary function tests (also called PFTs or breathing tests) evaluate how well your lungs work.  They help determine how much air your lungs can hold, how quickly you can move air in and out of your lungs, how deep of a breath you can take, and how well oxygen diffuses in and out of your lungs.



A PFT is performed to:

  • Evaluate how well your lungs and airways function
  • Diagnose certain lung disease, such as asthma or Chronic Obstructive Pulmonary Disease (COPD)
  • Evaluate a patient’s lung function before surgery.

About The Tests

How do I prepare?

Before a Pulmonary Function test, it is important not to do anything that might disturb your lung function.

  • Avoid smoking for several hours prior to your test
  • Avoid heavy meals before your test
  • Stop using inhalers, breathing treatments and sedatives for at least 4 hours prior to your test.
  • Continue any other medications you usually take.
  • Refrain from exercising for several hours before your test.
  • Wear loose-fitting, comfortable clothing.

What should I expect?


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You will be asked to sit inside a clear plexiglass booth, called a plethysmograph. The airtight booth measures small changes in pressure that occur as you breathe. You will wear a nose clip to make sure that no air passes in or out of your nose during the test and you will be asked to breathe into a mouthpiece.

PFTs are conducted by specially trained respiratory therapists who will tell you how to best breathe throughout the test. The exact procedure is different for each type of test.

Some of the tests are performed more than once to assure consistent results, while others may be repeated after you have inhaled a spray containing medication that expands the airways in your lungs, called a bronchodilator.

The accuracy of the tests depends on your ability to follow the therapist’s instructions.

Are there any risks?

The risk of injury from a PFT is very low. You will be monitored by a respirtory therapist, who will be seated less than five feet from you at all times. If claustrophobia is a significant problem for you, an alternative technique may be used to perform the testing. You may, however, experience some mild and temporary shortness of breath, dizziness or lightheadedness. If you feel any chest pain or discomfort, tell the therapist immediately.

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