COPD Diagnostic Tests: Pulmonary Function, Spirometry, and More
Pulmonary Function Testing (PFTs) continued...
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 helpful when preparing for lung surgery.
Before the day of your test, you may receive specific instructions on how to prepare for PFTs. These instructions may include:
- Asking you to not use certain kinds of medicines for a specific time period prior to your test, especially inhaled medicines.
- Asking you to wear loose clothing and avoid large meals prior to your test time. This will ensure that you can take deep breaths and perform the tests well.
You will get instructions right before each test. If you do not understand any of these instructions, ask questions! For best results, listen carefully and follow the coaching. Ask for a short rest between each of the tests if you become tired. If you normally use oxygen during the day, bring your oxygen with you.
PFTs are made up of several different tests that are described below.
Spirometry is the simplest lung function test that can be done. It can even be done in a doctor''s office, if he/she has the right equipment. Spirometry measures:
- How much air you can breathe in and out
- How fast you can breathe out that volume of airHow fast you can breathe out that volume of air
For many of these tests, you will be asked to breathe as forcefully as you can. Often, a test is repeated three or more times to make sure results are consistent and accurate. Spirometry is often performed before and after the patient is given an inhaled medicine called a "bronchodilator." Knowing how you respond to the bronchodilator will help your doctor know if one of these types of medicines will improve your breathing.
Here is a description of some of the more important spirometry measurements:
Forced Vital Capacity (FVC) measures the amount of air you can breathe out in one complete breath. You will hold a clean tube up to your mouth, often using a mouthpiece. You will be asked to breathe in as fully as you can. And then immediately blow out as hard and fast as you can, until you feel you cannot blow any longer. You will do this with your nose pinched closed. A new version of this test, called the "Six-Second Forced Expiratory Volume (FEV6)," is now sometimes being used. During this test, instead of breathing out as long as you can you are only required to breathe out for six seconds. This method has been shown to provide basically the same information as an FVC, but is easier to perform accurately. There is less risk of dizziness and fainting in patients with lung disease.
Forced Expiratory Volume in the first second (FEV1) measures how much of the air you blew out was breathed out during the first second. A decrease in the FEV1 may mean there is blockage to the flow of air out of your lungs. Obstructive pulmonary diseases, such as emphysema, asthma or chronic bronchitis, can cause reduced FEV1 values. This value is often the most important value followed over time in COPD patients.
The Ratio describes what percentage of your total breath was breathed out during the first second of your FVC test. It is calculated by dividing your actual FVC or FEV6 into your actual FEV1. The result is reported as a fraction or percentage. The normal adult can breathe out 60-90 percent of their breath during the first second. This percent often decreases with age. In obstructive lung diseases, the FEV1/FVC ratio is lower than the normal range. If you have both a low FEV1 and a low FVC, this value can help in understanding the type of lung disease you have.
Peak Expiratory Flow or Peak Flow (PEF) measures how fast air is breathed out from your lungs. It reports the fastest flow rate reached during a full breath or FVC. This normally occurs near the beginning of your forced breath out. PEF is very dependent on your effort. This type of testing can also be done at home using a Peak Flow Meter. It is a way of following your own lung function. This is done primarily to follow asthma. Studies are being done to see if this simple test can help suggest a COPD diagnosis.
Mid-Breath Forced Expiratory Flow (FEF25-70), also called "Maximum Mid-Expiratory Flow or MMEF, measures how fast you breathe out air from 25 percent of your breath to 75 percent of your breath. This measurement is a very sensitive test for small airway disease, which obstructs the breathing out of air, such as in asthma. In patients with moderate to severe COPD, the values given are usually too low to be useful in reviewing changes in lung disease.