Pulmonary Function Tests

What is pulmonary function testing?

Pulmonary function testing is sometimes called “PFT” or “breathing tests.”  This series of tests measures several things.  It determines the amount of air in your lungs, the amount of air you can inhale into your lungs, and the amount of air you can exhale from your lungs.  PFTs measure how much air moves in and out of the lungs. They also measure how fast the air moves in and out.

Why was a PFT ordered?

PFTs are ordered for many different reasons. Some reasons are:

  • As part of a routine physical exam, especially if you smoke or have a history of smoking
  • As part of a work physical, if the worker must wear a mask or respirator to perform the job
  • To test your lung function before surgery
  • To help diagnose lung conditions or diseases such as asthma, emphysema, chronic bronchitis, or pulmonary fibrosis
  • To check the extent of lung disease or to help explain new breathing symptoms
  • To find out if your breathing medicine is working
  • To check if you are having side effects from some medicines that can make breathing difficult

A PFT alone will not diagnose a disease. But it will help your doctor to make a correct diagnosis.

Before the Test

Talk with your doctor about your medicines before scheduling the PFT.  If you use an inhaler or take breathing medicine regularly, do not use or take those within 4 hours before your test.  Do not exercise before the PFT.  Save your energy so you can give your best effort during the test.  The day of the PFT, bring with you any breathing medicine that you take.  You may need your quick-relief inhaler during or after the test.  The PFT will take 45 minutes to 1 hour to complete.

The Testing Equipment

If you have had PFTs in the past, you might notice different equipment at different testing centers.  This is common.  Although equipment may look different, the tests are the same.

During the Test

Tell the person giving you the test if you:

  • Are dizzy or become light-headed
  • Have chest pain
  • Have shortness of breath
  • Feel nervous or feel that your heart is racing

Pulmonary Function Testing Methods

Spirometry tests

All testing centers use a spirometer (spi-RAH-meh-ter) to measure how much air you can breathe in and out.  The spirometer also measures how fast you can breathe in and out.  The spirometer is used for the following 3 tests:

Flow volume loop

The “flow volume loop” shows how much air you can forcefully exhale (forced vital capacity, or FVC).  It also shows how much air is exhaled in the first second of a forced exhalation (forced expired volume in one second, or FEV-1).  You will be asked to take a deep breath in and blow out as hard and as fast as you can through a mouthpiece. 

You will blow out until you feel there is no more air left in your lungs.  Keep your lips sealed tightly around the mouthpiece.  You will have a clip on your nose to keep you from exhaling through your nose.  All of the air you breathe in and out must be measured for the test to be accurate.  You will do this test at least 3 times to ensure an accurate reading.

Maximum voluntary ventilation (MVV)

Like the flow volume loop test, you will have a clip on your nose and your lips sealed tightly around a mouthpiece.  You will breathe deep and fast for 12 to 15 seconds, without stopping.  This test will also be done at least 3 times for accuracy.

Post bronchodilator testing

You may be asked to breathe in a medicine that will relax the muscles around the airway.  This medicine is called a bronchodilator (BRON-ko-DIE-lay-tor).  The medicine will make it easier to exhale.  After taking the medicine, the flow volume loop and MVV tests will be repeated. You will perform each test at least 3 times again.  The doctor who reads your test results will look to see if your lung function tests improved after taking the medicine.

Lung capacity tests

Lung capacity tests determine the total volume of air in the lung.  No matter how hard you blow out, a small volume of air still remains in the lung.  This amount of air left in your lungs is what allows you to take in your next breath with ease.  Lung capacity tests measure:

  • The normal amount of air that you breathe in and out
  • The maximum amount of air you can breathe in and out
  • The amount of air remaining in your lungs

The total of these is your “total lung capacity.”  The following 3 tests measure lung volumes and help determine total lung capacity:

  • Body plethysmography (pleth-is-MOG-reh-fee): For this test, you will sit inside a booth.  You will keep your lips sealed tightly around a mouthpiece with a clip on your nose.  You will be instructed to do 3 things without taking your mouth off of the mouthpiece:
  1. Breathe normally for several breaths.
  2. Take in a big, deep breath and blow out slowly.
  3. Lastly, pant (short rapid breaths) for a few seconds.

The amount of air remaining in your lungs is calculated using a formula.

  • Helium dilution method: For this test, you will keep your lips sealed tightly around a mouthpiece with a clip on your nose and breathe normally.  You will breathe in a mixture of helium and oxygen.  This test lasts 3 to 7 minutes.  At the end of this time, you will be told to take a deep breath in and blow out slowly.
  • Nitrogen washout: Again, you will be asked to keep a tight seal on the mouthpiece with a clip on your nose and breathe normally.  You will breathe in oxygen*.  This test lasts 3 to 7 minutes.  At the end of this time, you will be told to take a deep breath in and blow out slowly.
    • Tell the person giving you this test if a doctor has diagnosed you with lung disease. High levels of oxygen may be harmful to patients with lung disease.

Diffusion capacity/DLCO tests

This test determines how well the oxygen in your lungs is able to move to the bloodstream.  You will be asked to keep a tight seal on a mouthpiece with a clip on your nose and breathe normally.  After several breaths, you will take in as deep a breath as possible and blow it out slowly.  You will keep blowing out until you are told to take a deep breath in and hold it for 10 to 15 seconds.  Then, you will blow out again through the mouthpiece.

After the Test

You may feel tired when the PFT is completed.  Rest until you feel comfortable leaving the testing center.  If you missed any doses of your breathing medicine, ask the person giving the test if you can take them.

Once you leave the testing center, call your doctor if you have any shortness of breath, chest pain, or trouble breathing.

After your test is finished, the results will be reviewed by a doctor.  A report will then be sent to your doctor.  You will not receive any test results until your doctor sees the PFT analysis.  Remember, the PFT alone does not diagnose a disease.  But, it does help your doctor to make a correct diagnosis.

                                                                                                                                  Reviewed 7/11

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