Pulmonary Function Test

Pulmonary function tests (PFTs) are a group of tests that measure how well your lungs work.

Why are these tests done?

PFT assesses how well your lungs are working before you have surgery.

PFTs can help diagnose lung disease such as:

  • asthma
  • lung fibrosis
  • chronic obstructive pulmonary disease (COPD)

If you already have a condition that’s affecting your lungs, your doctor may order this test to see if the condition is progressing or how it’s responding to treatment.


How do I prepare for pulmonary function tests?

If you’re on medications that open your airways, such as those used for asthma or bronchitis, your doctor may ask you to stop taking them 4 to 6 hours before the test. If it isn’t clear whether or not you should take your medication, make sure to ask your doctor. 

It’s important that you don’t eat a large meal before testing. A full stomach can prevent your lungs from inhaling fully. Avoid food and drinks that contain caffeine, such as chocolate, coffee, and tea, before your test. You should also avoid smoking and strenuous exercise before the test.

Be sure to wear loose-fitting clothing to the test. Tighter clothing may restrict your breathing. If you wear dentures, wear them to the test to ensure that your mouth can fit tightly around the mouthpiece used for the test.


What tests are done to assess the lung function?

There are three primary phases of pulmonary function testing:

  • Spirometry
  • Lung volume measurement
  • Diffusion capacity measurement

Spirometry records the amount of air you can breathe in and out and the rate at which this process takes place. The therapist will ask you to breathe through a mouthpiece connected to a recording device. Spirometry reveals the degree of narrowing or obstruction of the airways.

Lung volume measure the amount of air your lungs can hold. The test is done while sitting in a plethysmograph, a transparent booth.

Gas diffusion tests are lung function tests that determine how efficiently the body is able to transfer oxygen from the lungs into the bloodstream. In the single-breath or breath-holding method, the patient will take a breath of air containing a very small amount of carbon monoxide from a container while measurements are taken.

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