Pulmonary Function Tests

What are pulmonary function tests?

Pulmonary function tests (PFTs) are tests that show how well your lungs are working. The tests measure lung volume, capacity, rates of flow, and gas exchange. This information can help your healthcare provider diagnose and decide the treatment of certain lung disorders.

There are several types of disorders that cause problems with air moving in and out of the lungs:

Obstructive. This is when air has trouble flowing out of the lungs because of airway resistance. This causes slower flow of air.
Restrictive. This is when the lung tissue or chest muscles can’t expand enough. This creates problems with air flow, mostly because you have less lung volume.

PFTs can be done in two ways. These two ways may be used together and do different tests. It depends on the information that your healthcare provider is looking for:

Spirometry. A spirometer is a device with a mouthpiece hooked up to a small electronic machine.
Plethysmography. You sit or stand inside an airtight box to do the tests.

PFTs measure:

Tidal volume. This is the amount of air breathed in or out during normal breathing.
Minute volume. This is the total amount of air breathed out per minute.
Vital capacity. This is the total volume of air that can be breathed out after breathing in as much as you can.
Functional residual capacity. This is the amount of air left in lungs after breathing out normally.
Residual volume. This is the amount of air left in the lungs after breathing out as much as you can.
Total lung capacity. This is the total volume of the lungs when filled with as much air as possible.
Forced vital capacity (FVC). This is the amount of air breathed out forcefully and quickly after breathing in as much as you can.
Forced expiratory volume. This is the amount of air breathed out during the first, second, and third seconds of the FVC test.
Forced expiratory flow. This is the average rate of flow during the middle half of the FVC test.
Peak expiratory flow rate. This is the fastest rate that you can force air out of your lungs.

Normal values for PFTs vary from person to person. The amount of air breathed in and out in your test results are compared with the average for someone of the same age, height, sex, and race. Results are also compared with any of your past test results. You may need other tests if you have abnormal PFT measurements or if your results have changed.

Why might I need pulmonary function tests?

There are many different reasons why pulmonary function tests (PFTs) may be done. They are sometimes done in healthy people as part of a routine physical. They are also routinely done in certain types of work environments to make sure of employee health. This might be in graphite factories or coal mines. Or you may have PFTs if your healthcare provider needs help to diagnose you with a health problem. These include:

Allergies
Respiratory infections
Trouble breathing from injury to the chest or a recent surgery
Long-term (chronic) lung conditions, such as asthma, bronchiectasis, emphysema, or chronic bronchitis
Asbestosis, a lung disease caused by inhaling asbestos fibers
Restrictive airway problems from scoliosis, tumors, or inflammation or scarring of the lungs
Sarcoidosis, a disease that causes lumps of inflammatory cells around organs, such as the liver, lungs, and spleen
Scleroderma, a disease that causes thickening and hardening of connective tissue

PFTs may be used to check lung function before surgery or other procedures. This may be done in people who have lung or heart problems, who are smokers, or who have other health conditions. Another use of PFTs is to assess treatment for asthma, emphysema, and other chronic lung problems. Your healthcare provider may also have other reasons to advise PFTs.

What are the possible risks of pulmonary function tests?

Because pulmonary function testing is not an invasive procedure, it is safe and quick for most people. But the person must be able to follow clear, simple directions.

All procedures have some risks. The risks of this procedure may include:

Dizziness during the tests
Feeling short of breath
Coughing
Asthma attack brought on by deep inhalation

In some cases, you shouldn’t have PFTs. Reasons for this can include:

Recent eye surgery, because of increased pressure inside the eyes during the procedure
Recent belly or chest surgery
Chest pain, recent heart attack, or an unstable heart condition
A bulging blood vessel (aneurysm) in the chest, belly, or brain
Active tuberculosis or respiratory infection, such as a cold or the flu

Your risks may vary depending on your general health and other factors. Ask your healthcare provider which risks apply most to you. Talk with them about any concerns you have.

Certain things can make PFTs less accurate. These include:

Not following the instructions for doing the test
Using medicines that open the airways (bronchodilators)
Using pain medicines
Pregnancy
Stomach bloating. This can affect your ability to take deep breaths
Extreme tiredness or other conditions, such as a head cold, that affect your ability to do the tests

How do I get ready for pulmonary function tests?

Your healthcare provider will explain the procedure to you. Ask any questions you have. You may be asked to sign a consent form that gives permission to do the procedure. Read the form carefully. Before you sign the consent form, ask questions if anything isn't clear.

Tell your healthcare provider if you take any medicines. This includes prescription and over-the-counter medicines, vitamins, herbs, and other supplements.

Also:

Stop taking certain medicines before the procedure if told to do so by your healthcare provider.
Stop smoking before the test if told to do so by your healthcare provider. Ask your provider how many hours before the test you should stop smoking.
Follow any directions you are given by your provider for not eating or drinking before the test.
Follow any other instructions your healthcare provider gives you.

Your height and weight will be recorded before the test. This is done so that your results can be accurately calculated.

What happens during pulmonary function tests?

You may have your test as an outpatient. This means you go home the same day. Or it may be done as part of a longer stay in the hospital. The way the test is done may vary. It depends on your condition and your healthcare provider's methods. In most cases, the test will follow this process:

You’ll be asked to loosen tight clothing, jewelry, or other things that may cause a problem with the test.
If you wear dentures, you will need to wear them during the test.
You’ll need to empty your bladder before the test.
You’ll sit in a chair. A soft clip will be put on your nose. This is so all of your breathing is done through your mouth, not your nose.
You’ll be given a disposable mouthpiece that is attached to a spirometer.
You’ll form a tight seal over the mouthpiece with your mouth. You’ll be instructed to inhale and exhale in different ways.
You will be watched carefully during the test for dizziness, trouble breathing, or other problems.
You may be given a bronchodilator after certain tests. This medicine causes widening of the bronchi, the large air tubes that lead from the windpipe (trachea) to the lungs. The tests will then be repeated several minutes later, after the bronchodilator has taken effect.

What happens after pulmonary function tests?

If you have a history of lung or breathing problems, you may be tired after the tests. You will be given a chance to rest afterwards. Your healthcare provider will talk with you about your test results.

Next steps

Before you agree to the test or procedure make sure you know:

The name of the test or procedure
The reason you are having the test or procedure
What results to expect and what they mean
The risks and benefits of the test or procedure
What the possible side effects or complications are
When and where you are to have the test or procedure
Who will do the test or procedure and what that person’s qualifications are
What would happen if you did not have the test or procedure
Any alternative tests or procedures to think about
When and how will you get the results
Who to call after the test or procedure if you have questions or problems
How much you will have to pay for the test or procedure