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Pulmonary function tests PFT:

Pulmonary function tests are a group of tests that measure how well the lungs take in and release air and how well they move gases such as oxygen from the atmosphere into the body's circulation.

PULMONARY FUNCTION TESTS  The major types of pulmonary function tests include spirometry, measurement of lung volumes, and quantitation of diffusing capacity. Measurements of maximal respiratory pressures and flow-volume loops, which record forced inspiratory and expiratory flow rates, are also useful in specific clinical circumstances.

Spirometry

Spirometry includes tests of pulmonary mechanics – measurements of FVC, FEV1, FEF values, forced inspiratory flow rates (FIFs), and MVV. Measuring pulmonary mechanics assesses the ability of the lungs to move large volumes of air quickly through the airways to identify airway obstruction.

The measurements taken by the spirometry device are used to generate a pneumotachograph that can help to assess lung conditions such as: asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease. Physicians may also use the test results to diagnose bronchial hyperresponsiveness to exercise, cold air, or pharmaceutical agents

Lung volumes

Common lung volume measurements include total lung capacity (TLC), functional residual capacity (FRC), and residual volume (RV) . Measurement of the total lung capacity (TLC) may be helpful when the vital capacity is decreased. For example, in the setting of chronic obstructive pulmonary disease (COPD) with a low vital capacity, measurement of the TLC can help determine if there is a superimposed restrictive disorder.

There are four methods of measuring TLC:

●Helium dilution

●Nitrogen washout

●Body plethysmography

●Chest radiograph measurements

The first two methods are used extensively in hospital pulmonary function laboratories, but they may underestimate the TLC in patients with moderate to severe COPD. The gold standard for measurement of TLC, particularly in the setting of significant airflow obstruction, is body plethysmography.

Measurements of TLC using the chest radiograph or high resolution computed tomography (HRCT) correlate within 15 percent of those obtained by body plethysmography . Since the TLC is equivalent to the amount of air seen in the lungs on a chest radiograph taken at maximal inspiration, it is important that the subject inhales maximally as the image is created.

Pulmonary function tests is an inclusive term that refers to several different procedures that measure lung function in different ways. Some of the more common values that may be measured during pulmonary function testing include:

·         Tidal volume (VT). This is the amount of air inhaled or exhaled during normal breathing.

·         Minute volume (MV). This is the total amount of air exhaled per minute.

·         Vital capacity (VC). This is the total volume of air that can be exhaled after maximum inspiration.

·         Functional residual capacity (FRC). This is the amount of air remaining in lungs after normal expiration.

·         Total lung capacity. This is the total volume of lungs when maximally inflated.

·         Forced vital capacity (FVC). This is the amount of air exhaled forcefully and quickly after maximum inspiration.

·         Forced expiratory volume (FEV). This is the volume of air expired during the first, second, and third seconds of the FVC test.

·         Forced expiratory flow (FEF). This is the average rate of flow during the middle half of the FVC test.

·         Peak expiratory flow rate (PEFR). This is the maximum volume during forced expiration.

The normal values for PFTs vary from person to person. The amount of air inhaled and exhaled in your test results are compared to the expected average in someone of the same age, height, sex, and race. In addition, results are compared to your previous test results, if previous testing has been done. If you have abnormal PFT measurements or if your results are different from previous tests, you may be referred for other diagnostic tests to establish a medical diagnosis.

Reasons for the procedure

There are many different reasons why PFTs may be ordered. They are sometimes ordered in healthy individuals as part of a routine physical. In others, the tests may be ordered when a specific illness is suspected. Some of the disorders that may be detected with PFTs include, but are not limited to, the following:

·         Allergies. An acquired, abnormal immune response to one or more substances that can cause a broad range of inflammatory reactions.

·         Chronic lung conditions. Conditions, such as asthma, bronchiectasis, emphysema, and chronic bronchitis, that can be treated but not cured.

·         Asbestosis. A lung disease caused by the inhalation of asbestos fibers.

·         Chest trauma. Trauma to the chest, such as fractured ribs or a recent surgical procedure, can restrict an individual’s ability to breathe adequately.

·         Restrictive airway conditions. Impaired lung expansion as a result of conditions, such as scoliosis, pulmonary tumors, or inflammation or scarring of the chest wall.

·         Respiratory infections.

·         Sarcoidosis. A condition that causes small, fleshy swellings in the tissue around the organs, usually in the liver, lungs, and spleen.

·         Scleroderma. A disease of the body’s connective tissue that causes thickening and hardening of the skin.

·         PFTs may be used to assess the lung function of patients prior to surgery or other invasive procedures in patients who have current lung and/or heart problems, who are smokers, or who have other conditions that might be affected by surgery or other procedures.

·         Another use of PFTs is the evaluation of treatment for conditions such as asthma, emphysema, and other chronic lung problems.

·         There may be other reasons for your doctor to recommend pulmonary function tests.

Before the procedure

·         Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

·         Generally, no prior preparation, such as fasting, fluid restriction, or sedation is required. However, you may be asked to avoid eating a heavy meal before the test.

·         If you are pregnant or suspect that you may be pregnant, you should notify your doctor.

·         Notify your doctor of all medications (prescription and over-the-counter) and herbal supplements that you are taking.

·         If you are a smoker, you will usually be asked to refrain from smoking for a period of time before the test.

·         Your height and weight will be recorded so that your results can be accurately calculated.

·         Based on your medical condition, your doctor may request other specific preparation.

During the procedure

Pulmonary function tests may be done on an outpatient basis or as part of your stay in the hospital. Procedures may vary depending on your condition and your and your doctor’s practices.

Generally, PFTs follow this process:

·         You will be asked to loosen tight clothing, jewelry, or other objects that may interfere with the procedure

·         If you wear dentures, you will be asked to wear them during the procedure.

·         You will be asked to empty your bladder before the procedure to optimize comfort.

·         You will sit in a chair or stand for the procedure.

·         You will be given a soft nose clip to wear during the procedure so that all of your breaths will go through your mouth, rather than your nose.

·         You will be given a sterile mouthpiece that will be attached to the spirometer.

·         With your mouth forming a tight seal around the mouthpiece, you will be instructed to perform various breathing maneuvers. The maneuvers will be done by inhaling and exhaling. Depending on what measurements are ordered, you may be asked to repeat the maneuvers several times before the test is completed.

·         You may be given a bronchodilator after certain tests have been performed. These tests will be repeated several minutes later after the bronchodilator has taken effect.

·         You will be monitored carefully during the procedure for faintness, dizziness, difficulty breathing, or any other problems.

After the procedure

Generally, there is no special type of care following PFTs. You may resume your usual diet, medications, and activities unless your doctor advises you otherwise.

If you have a history of respiratory problems, you may be tired after the procedure. You will be given the opportunity to rest afterwards.

Your doctor may give you additional or alternate instructions after the procedure depending upon your particular situation.

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