Understanding Pulmonary Function Tests

What Are Pulmonary Function Tests?

PFTs. Getty Images

What are pulmonary function tests or PFTs?

Also known as PFTs, pulmonary function tests measure how well your lungs are working and the degree of impairment you may have due to asthma. They tell your doctor how well your lungs will be able to deliver oxygen to the rest of the body.

When Will My Doctor Order PFTs

There are a number of reasons that your doctor may order pulmonary function tests in order to assess and monitor your asthma control.

Your doctor may order PFTs when you experience asthma symptoms such as:

Spirometry, for example, is an objective measurement that can be used to determine how well your asthma control is doing. These tests may also be ordered if there is some question about an asthma diagnosis. Finally, these tests can also be part of an evaluation for occupational asthma or a number of other complaints or health conditions.

Pulomonary function tests may also be ordered if your doctor is concerned about a diagnosis of:

  • asbestosis
  • allergies
  • chronic bronchitis
  • bronchiectasis
  • chronic obstructive pulmonary disease (COPD), which is also called “emphysema”
  • lung cancer
  • lung fibrosis
  • lung mass
  • respiratory infections
  • sarcoidosis
  • scleroderma

What Are The Different Types Of Pulmonary Function Tests

There are a number of different pulmonary function tests that your doctor may order. These include:

  • Spirometry. This tests basically looks at your lung’s capacity to move air in and out. You breathe in and then forcefully exhale through a mouthpiece. Your specific measurements are compared and expressed as a percent of the measurements of other healthy people of the same race, age, gender, height and weight. FEV1, or the maximal amount of air you can forcefully exhale in one second, is the most commonly used measure.
  • Post Bronchodilator Spirometry. Same test as above, but preformed both before and after rescue inhaler or other bronchodilator use. This test indicates possible reversibility of airflow. Improvement of FEV1 by 12% is considered significant.
  • Volume Loops. Flow volume loops are preformed as part of both inspiration and expiration. This maneuver can help aid in some other causes of wheezing such as vocal chord dysfunction because of characteristic patterns of the volume loop.
  • Lung Volumes. These tests measure the amount of air in your lungs. Depending on the disease process you may have overinflated or decreased amounts of air in the lungs.
  • Six Minute Walk Test. This test is an objective measure of how far you can walk in six minutes, but is not commonly used in asthma.
  • Arterial Blood Gas. A blood test that assesses oxygenation from arterial blood.
  • Diffusing Capacity. This test measures how well oxygen gets into your blood stream. The rest requires that you breathe in a certain gas and then your exhalations are monitored by breathing out through a tube.

How Do I Prepare For Pulmonary Function Tests?

If you are taking inhalers for asthma, your doctor may or may not want you to take your medication before the test.

Sometimes they will give you a specific time so the test may be done in a certain time after your medication. Other medications can sometimes impact your PFT results. Make sure your doctor knows about all your medications, especially pain medications and others that can directly impact the lungs.

You also need to know if you can eat before your test. Eating a large amount of food might not only inhibit your performance with PFTs, but the test itself could lead to vomiting if attempted on a full stomach. You also need to be mindful of certain foods and drinks. Caffeine, for example, is one substance that can directly impact tissues in the lungs (it provides a certain amount of bronchodilation.

As a result it is best to avoid soda, chocolate, coffee, and tea before your test. You should also avoid smoking or significant activity that would increase your fatigue levels before the test.

Finally, you will want to not wear anything that is restrictive that might impair your test performance. As tight clothing such as spandex  is restrictive, you will want to wear loose fitting clothes as well as avoiding jewelry that might impact your breathing. If you wear dentutes you will need to see if you can leave them in during the test as it might be more difficult to achieve a good seal while wearing them.

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  1. National Heart, Lung, and Blood Institute. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma.
  2. Centers For Disease Control. Asthma.

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