A pulmonary function test known as spirometry measures the rate of air flow in and out of the lungs, and a person’s estimated lung size.
Spirometry is just one of the tests used to diagnose pulmonary fibrosis (PF). No single test is definitive, so physicians often order up a battery of exams to come up with a diagnosis.
Spirometry tests can be used to help diagnose a number of lung diseases, including asthma, chronic obstructive pulmonary disease (COPD) and other conditions that affect breathing. The test can also be used to see if a treatment is effective.
What are air flow rates?
Air flow rates are measurements of the amount of air passing through the lungs in a specific period.
Key spirometry air flow measurements include:
- Forced vital capacity (FVC) – This is a measurement of lung size, in liters. It represents the volume of air in the lungs that can be exhaled after a deep inhaled breath.
- Forced expiratory volume in one second (FEV-1) – This measures how much air can be exhaled in one second after a deep inhaled breath.
Low FVC values indicate restricted breathing. Low FEV-1 values indicate significant obstruction.
When you receive your spirometry results, you will likely see an FEV1/FVC ratio. This number represents the percent of the lung size (FVC) that can be exhaled in one second. If the FEV1 is 4 and FVC is 5, then the FEV1/FVC ratio would be 4/5 or 80 percent. This means the patient can breathe out 80 percent of the air inhaled into the lungs in one second.
How does a spirometry test work?
A spirometry test requires you to breathe into a tube attached to a device called a spirometer. Before you perform the test, a doctor or nurse will give you instructions. Make the most of this pre-test moment to clarify questions you may have.
During the test, you will likely be seated, and a clip will be placed on your nose to keep your nostrils closed.
You will be told to take a deep breath and breathe out as hard as you can for several seconds. Make sure your lips seal the tube you are exhaling into, so no air escapes.
You’ll need to repeat the test at least three times, to even out the results. If there is a lot of variation in the results, you may be asked to repeat the test an additional time. The combined results are the final result. Usually, the entire testing and feedback process takes no more than 15 minutes.
Your doctor may give you a bronchodilator medicine to open your lungs after an initial round of spirometry. You’ll then need to wait 15 minutes and repeat the test. Your doctor will compare the results with and without the bronchodilator’s help.
How to prepare for the test
Ask your doctor before the test if you should stop using inhaled-breathing or other medications you are using, and how long you should stop before the test.
Be sure to wear loose clothing that does not affect your ability to take a deep breath. And avoid eating a big meal before the test, so it’s easier to breathe.
What are the risks involved with the test?
Spirometry is safe. You may feel dizzy or experience shortness of breath right after the test but this will go away. If you recently had a heart attack or other heart-related episode, you should not take a spirometry test. On rare occasions, the test has triggered worse breathing problems for a patient.
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