Pulmonary Function Test
Individuals with COPD often have abnormal PFT results which suggest airway blockage and air trapping. Similar changes can be seen in some other lung conditions, such as asthma. If the lung function testing includes a diffusing capacity (DLCO) test, a low value suggests emphysema.
Many factors can affect the results of these tests. These include the current health of your lungs, the skill of the person testing you, your effort and the type of equipment used. PFTs are helpful in measuring the effects of lung medicines on lung function. They can also determine how serious are the disorders affecting the airways or other lung tissue. PFTs are also helpful when preparing for lung surgery.
How is Pulmonary Function Test (PFT) performed?
A qualified technician will ask you to breath at different speeds and depths through a special device that can measure the airflows and volumes of your lungs. On some tests you will also breathe different amounts of oxygen. The technician will ask you to repeat most of the tests several times, to ensure that the results are repeatable and an accurate and valid reflection of your lung function. To minimize the number of trials you will have to perform, and to get the most accurate results, listen closely to your technician as (s)he guides you through the testing.
How long does the test last?
A pulmonary function test may take 30 to 60 minutes to complete. This will vary according to the amount of trials necessary for you to get repeatable test results.
What are the tests of Pulmonary Function Test (PFT)?
The tests that make up a full PFT are:
- Flow Volume Loops, before and after bronchodilator
The flow-volume loop obtained during the spirometry manoeuvre can have four distinctive shapes that are linked to certain pathologies: obstructive lung disease, restrictive lung disease, mixed lung disease and upper airway obstructions. The shape of the flow-volume loop can indicate the location of airflow limitation, such as the large upper airways or smaller distal airways. With common obstructive airflow disorders, such as asthma or emphysema, the disease generally affects the expiratory limb and can reduce the effort-dependent peak expiratory flow as well as subsequent airflows that are independent of effort. The descending limb of the expiratory loop is typically concave. In contrast, several unusual anatomic disorders that narrow the large airways can produce a variety of patterns of truncation or flattening of either one limb of the loop (variable upper airway obstruction) or both limbs of the loop (fixed upper airway obstruction).
- Gas Transfer
This test is used to assess the ability of the lungs to diffuse inhaled oxygen from the lungs into the bloodstream and is the most common test performed after spirometry. It is often performed in conjunction with spirometry and lung volumes as part of a Complex Lung Function Test. This test involves the inhalation of a test gas which is held for 10 seconds then blown out. A sample of the exhaled test gas is collected and analysed and compared to your predicted values. A change in concentration of the test gas reflects how well your lung tissue (parenchyma) is able to deliver oxygen to the red blood cells in the bloodstream. You may be asked to have a blood test if your diffusing capacity is impaired to exclude anaemia.
- Lung Volumes (Body Plethysmography)
The lung volume test tells us how much air is left behind when you breath out, which can help your doctor discover what condition you may have present in your lungs.The test uses the nitrogen washout technique and takes about 20 mins. You will be required to gently breathe in and out through a mouthpiece and the test is not uncomfortable. This test requires you to breathe in 100% oxygen, and then the nitrogen in the lungs is washed out and measured. Exhaled Nitrogen is used to determine lung volumes in this test since normal room air that you breathe contains higher concentrations of Nitrogen (78%) compared to Oxygen, which is only 21%. It is important that your lips remain tightly sealed around the mouthpiece to prevent contamination with room air during the test. The scientist is able to detect any leaks during the test.
How should I prepere for Pulmonary Function Test (PFT)?
Various activities may influence your lung function and should be avoided before testing. For at least 3 hours before your test you should not eat or drink anything (you can drink water). If your stomach is full of food it will press on your lungs preventing them from expanding when you take a deep breath. Additionally, caffeine should not be taken before your test because it can cause the air tubes in your lungs to constrict. If possible, you should not smoke on the day of the test. If you are unable to do this, try to avoid smoking for several hours before your test. This is important because smoking can change the way your lungs function and it influences the blood that flows through your lungs. Be sure not to wear tight clothing that constricts your chest or prevents you from taking a very deep breath. Bring a list of your current medications with you to your test. Your doctor’s office will tell you if you are supposed to take your medications before the test, but if you are unsure, contact your doctor. If you have any questions about your test please contact your doctor’s office and ask to speak with the technician. (S)he will answer any questions you might have, or direct you to the proper person who can answer your questions.
- Medical Conditions
- Chronic obstructive pulmonary disease
- Heart failure
- Coalworker's pneumoconiosis
- Occupational lung disease
- Occupational asthma
- Farmer's lung