Pulmonary Function Tests | Johns Hopkins Medicine

what are pulmonary function tests?

Pulmonary function tests (PFTs) are non-invasive tests that show how well the lungs are working. tests measure lung volume, capacity, flow rates, and gas exchange. This information can help your health care provider diagnose and decide on treatment for certain lung disorders.

There are 2 types of disorders that cause problems with the air moving in and out of the lungs:

  • obstructive. this is when air has trouble moving out of the lungs due to airway resistance. this causes a decrease in airflow.

  • restrictive. this is when the lung tissue and/or chest muscles cannot expand enough. this creates problems with airflow, primarily due to lower lung volumes.

    pft can be done with 2 methods. These 2 methods may be used together and perform different tests, depending on what information your health care provider is looking for:

    • spirometry. A spirometer is a device with a mouthpiece connected to a small electronic machine.

    • plethysmography. you sit or stand inside an airtight box that looks like a small, square phone booth to do the tests.

      pft measurements:

      • tidal volume (vt). is the amount of air inhaled or exhaled during normal breathing.

      • volume per minute (mv). this is the total amount of air exhaled per minute.

      • vital capacity (vc). is the total volume of air that can be exhaled after inhaling as much as you can.

      • functional residual capacity (frc). is the amount of air remaining in the lungs after normal exhalation.

      • residual volume. This is the amount of air left in your lungs after you exhale 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). is the amount of air exhaled forcefully and quickly after inhaling as much as you can.

      • forced expiratory volume (fev). this is the amount of air exhaled during the first, second, and third seconds of the fvc test.

      • forced expiratory flow (fef). this is the average flow rate during the middle half of the fvc test.

      • peak expiratory flow rate (pefr). this is the fastest rate at which you can push air out of your lungs.

        Normal pft values ​​vary from person to person. The amount of air inhaled and exhaled in your test results is compared to the average for someone of the same age, height, gender, and race. the results are also compared to any of your previous test results. If you have abnormal PFT measurements or if your results have changed, you may need other tests.

        why might you need lung function tests?

        There are many different reasons why pulmonary function tests (pft) may be done. they are sometimes done on healthy people as part of a routine physical exam. they are also routinely performed in certain types of work environments to ensure the health of employees (such as graphite factories and coal mines). or you may have pft if your healthcare provider needs help diagnosing a health problem such as:

        • allergies

        • respiratory infections

        • shortness of breath due to chest injury or recent surgery

        • chronic lung conditions, such as asthma, bronchiectasis, emphysema, or chronic bronchitis

        • asbestosis, a lung disease caused by inhalation of asbestos fibers

        • airway restriction problems from scoliosis, tumors, or inflammation or scarring of the lungs

        • sarcoidosis, a disease that causes clusters 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 monitor lung function before surgery or other procedures in patients who have lung or heart problems, who smoke, or who have other medical conditions. Another use of PFTs is to evaluate the treatment of asthma, emphysema, and other chronic lung problems. Your health care provider may also have other reasons for recommending PFTs.

          what are the risks of lung function tests?

          Because pulmonary function tests are a non-invasive procedure, they are safe and quick for most people. but the person must be able to follow clear and simple instructions.

          all procedures have some risks. Risks of this procedure may include:

          • dizziness during tests

          • feeling short of breath

          • cough

          • asthma attack caused by deep inhalation

            in some cases, a person should not have pfts. reasons for this may include:

            • recent eye surgery, due to increased pressure inside the eyes during the procedure

            • recent abdominal or chest surgery

            • chest pain, recent heart attack, or an unstable heart condition

            • a bulging blood vessel (aneurysm) in the chest, abdomen, or brain

            • active tuberculosis (tb) or respiratory infection, such as a cold or flu

              Your risks may vary based on your general health and other factors. ask your health care provider which risks apply most to you. talk to him or her about any concerns you have.

              Certain things can make pfts less accurate. these include:

              • the degree of patient cooperation and effort

              • use of medicines that open the airways (bronchodilators)

              • use of analgesics

              • pregnancy

              • stomach distention that affects the ability to breathe deeply

              • extreme tiredness or other conditions that affect a person’s ability to test (such as a cold)

                how do i prepare for lung function tests?

                Your healthcare provider will explain the procedure to you. ask him any questions you have. You may be asked to sign a consent form that gives permission to perform the procedure. Please read the form carefully. ask questions if something is not clear.

                Tell your healthcare provider if you take any medications. this includes prescriptions, over-the-counter medications, vitamins, and herbal supplements.

                make sure:

                • stop taking certain medications before the procedure, if directed by your health care provider

                • Stop smoking before the test, if your health care provider tells you to. ask your provider how many hours before the test you should stop smoking.

                • do not eat a heavy meal before the test, if directed by your health care provider

                • follow any other instructions your health care provider gives you

                  Your height and weight will be recorded prior to testing. this is done so that your results can be calculated accurately.

                  what happens during pulmonary function tests?

                  You can have your procedure as an outpatient. this means that you go home the same day. or it may be done as part of a longer hospital stay. the way the procedure is performed can vary. it depends on your condition and your health care provider’s methods. In most cases, the procedure will follow this process:

                  1. You will be asked to loosen any tight clothing, jewelry, or other things that may cause a problem with the procedure.

                  2. If you wear dentures, you will need to wear them during the procedure.

                  3. You will need to empty your bladder before the procedure.

                  4. you will sit in a chair. A soft clip will be placed on your nose. this is so that all your breathing is done through your mouth, not your nose.

                  5. You will be given a sterile mouthpiece that connects to a spirometer.

                  6. You will form an airtight seal over the mouthpiece with your mouth. you will be instructed to breathe in and out in different ways.

                  7. You will be watched closely during the procedure for dizziness, shortness of breath, or other problems.

                  8. You may be given a bronchodilator after certain tests. the tests will 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 feel tired after the tests. you will be given a chance to rest afterwards. your health care provider will discuss your test results with you.

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