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Pulmonary Function Tests


What do I need to know about pulmonary function tests?

Pulmonary function tests (PFTs) measure how well your lungs work. PFTs may show the cause of breathing problems or how well treatments for a lung condition are working.

How do I prepare for PFTs?

Your healthcare provider will talk to you about how to prepare for these tests. You may need to stop taking certain breathing medicines from several hours to 24 hours before your tests. He will tell you what other medicines to take or not take on the day of your test. If you use oxygen, you may need to stop using it for a short time before you have these tests. You may be told not to smoke or do intense exercise on the day of your tests.

What will happen during PFTs?

  • Spirometry measures how much air you breathe in and breathe out, and how fast you can blow air out. During this test, you will sit or stand next to a machine. A healthcare provider will place soft clips on your nose. He will tell you how to breathe into the machine. You will be asked to breathe calmly several times, draw the deepest breath you can, and then exhale forcefully for about 6 seconds. You will then be asked to breathe in deeply once more.
  • Lung diffusion capacity measures how well your lungs can move oxygen into your bloodstream. For this test, you will breathe in a gas through a tube. You will be asked to hold your breath for about 10 seconds and then exhale.
  • Body plethysmography measures the amount of air in your lungs after you take a deep breath. It also measures how much air stays in your lungs after you exhale. You will sit inside of a sealed box about the size of a phone booth. You will be asked to breathe into a tube that is connected to a computer. The healthcare provider will tell you how to breathe into this tube.

What are the risks of PFTs?

Deep breathing done during some tests may cause you to feel short of breath, dizzy, or lightheaded. It may also cause you to cough.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.