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The Pulmonary Function Test

Posted Apr 28 2013 9:28am

If the doctor has sent to you to a pulmonary function test, and you are wondering what exactly it is, here is a short resume for your information.

The pulmonary function test is rather a group of physical tests, which are performed to measure the ability of the lungs and airways to inhale and exhale, and the way they are able to intake oxygen and other gases into the circulation of the body.  The results will show if the lungs are affected or damaged by an illness, exposure to asbestos, smoking, etc.

The reason your doctor may have asked you to undergo such a test can be that you have a congested chest, shortness of breath, persistent coughing and sputum extraction, to see if your work or living environment isn’t affected your breathing, or as a test to see if medications and treatment prescribed to you for a lung or other breathing problem are working.

The types of pulmonary function tests

One pulmonary function test is the spirometry test, which is actually a measure of the volume and speed of the air you can exhale from your lungs. It is a simple test done with an instrument called a spirometer, and you will be asked to exhale into a mouthpiece, so that the volume and speed of your breath can be recorded. Depending on the reasons for the test, the doctors may ask you to simply breathe normally, or to breathe out as much air as you can after filling your lungs with air.

Another possible pulmonary function test, which can be performed to measure the volume of air in the lungs, is through a body plethysmograph , which is a well-sealed container, which you will be asked to sit in and inhale and exhale through a mouthpiece.  The doctors will measure the pressure deviations in the container and this is actually the most accurate test for measuring lung volume.

To test the lung volume, other pulmonary function tests can be done by breathing in and out harmless gas such as nitrogen or helium for a short period of time, and measuring the concentration of the gas in the container, the lung volume can be measured as well.

The way the respiratory system is able to intake gas and transport it to your circulation can be measured through breathing a “tracer” gas, once again a harmless gas. The concentration of the gas exhaled and inhaled is measured in order to see the effectiveness of the lungs and measure their diffusion capacity.

In order to get correct measurements during a pulmonary function test, you should abstain from eating, smoking or inhaling medication (if requested by your doctor) for at least 5 hours prior to the test.

The results of a pulmonary function test are interpreted by the doctors in percentages based on your height, age, sex and ethnicity. Normal results are those which are 80% or more that the value predicted for your specific case. If both the FVC (forced vital capacity) and FEV1 (forced expiratory volume in one second) are normal, then everything is alright with your lungs.

Results which are lower can mean that you have some sort of a chest or lung health problem, including obstructive lung disorders (COPD, cystic fibrosis, pneumonia and bronchitis), lung cancer, asbestosis, and restrictive lung disease such as: sarcoidosis, scoliosis etc.

Obstructive lung disorders in general are those health conditions which cause the person affected to be unable to exhale all the air from the lungs. This usually leads to shortness of breath, and is commonly caused by COPD, asthma or cystic fibrosis.


The restrictive lung disorders are the cases when the person cannot fill their lungs to the maximum. The causes often are: the autoimmune disease sarcoidosis, obesity, muscular dystrophy, scoliosis and others.

Usually, when reading the results of a pulmonary function test, especially the spirometric test, if the FEV1/FVC results are 69% or less the cause is most probably an obstructive disease.

The results from the spirometric tests are crucial when determining the stages (grade) of COPD in accordance to the GOLD grading system, introduced by the Global Initiative for Chronic Obstructive lung disease.  The spirometric results are read in accordance to the percentages in this 4-stage grading system, and the conclusions regarding the severity of COPD are crucial for the prescription of proper medical treatment to manage the condition.

It can be concluded that the pulmonary function test is a series of quite simple medical tests, but they are crucial when it comes to identifying, diagnosing and treating problems with the lungs and the whole respiratory system.

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