Breaking Down a Pulmonary Function Test (PFT)

by John Bottrell Health Professional

Pulmonary Function Testing (PFT) is a standard test that can help diagnose chronic obstructive pulmonary disease (COPD). The results may also determine how severe your disease is, and how well treatment is working.

A main part of the testing involves placing your mouth over a mouthpiece, blocking your nose with clamps, inhaling as deeply as you can, and forcibly exhaling as long and hard as you can until no more breath comes out. These results are recorded.

  • FVC. Forced Vital Capacity. Total amount of air you can exhale after deep inhalation.

  • TLC. Total Lung Capacity. How much air remains in your lungs after you completely exhale.

  • RV. Residual Volume. Air that remains inside your lungs even after the most forcible exhalation. Some air stays inside to keep your lungs open.

  • FEV1. Forced Expiratory Volume at the one second mark of FVC.

  • FEV1/ FVC. Expresses FEV1 as a percentage of the predicted value. This test is very sensitive, and a good measure of severity.

By looking at these numbers you can answer the following questions:

Do you have emphysema? Emphysema is a restrictive disease, meaning it prevents you from taking in a deep breath and fully expanding your lungs.

  • FVC is decreased. Loss of lung tissue means you cannot fully expand your lungs. You will have less air to blow out.

  • TLC is decreased or normal. Loss of lung tissue means you cannot move as much air in and out.

  • RV is decreased. With less space for air to move, the amount of air that remains in your lungs will be less.

  • FEV1/ FVC is increased or normal. Even though you have less space to move air, you should be able to blow out as much air as though your lungs were normal. It’s just that you won’t have much air left to exhale after this point.

Do you have chronic bronchitis? Bronchitis is an obstructive disease, meaning it causes airways to become narrowed or blocked in some way.

  • FVC is normal or decreased. It may be low because air trapped inside your lungs makes it difficult to take in a normal sized inhalation.

  • TLC is increased. Air can be easily inhaled through narrowed airways, but has trouble getting out. This causes air to become trapped in your lungs, called air trapping.

  • RV is increased. This is due to chronic air trapping.

  • FVC/ FEV1 is decreased. This is due to airflow limitation, and is indicative of the prolonged exhalation so frequently seen in chronic bronchitis.

How severe is your chronic bronchitis? A good way of checking severity of airflow limitation is to monitor FEV1.

  • Normal**.** FEV1 is 80% of predicted

  • Mild**.** FEV1 is 65-79% of predicted

  • Moderate**.** FEV1 is 50-64% of predicted

  • Severe**.** FEV1 is 35-49% of predicted

  • Very Severe**.** FEV1 is below 35% of predicted

How reversible is your chronic bronchitis? In other words, how much does your breathing improve with treatment? This involves doing all the initial PFT tests. You will then take an albuterol breathing treatment, wait 20 minutes, and repeat testing. You will then observe how much FEV1 improves.

  • Slightly Reversible: 15-25% improvement

  • Moderate Reversible: 25-50% improvement

  • Markedly Reversible. 50% improvement

How severe is your emphysema? This is determined by performing a Lung Diffusion Capacity Test (DLCO). You place your lips over a mouthpiece, clip your nose closed, and inhale as deep as you can. You then exhale completely. The test determines how effective your lungs are at getting oxygen into your blood, and carbon dioxide out of your blood.

A result of 50% or less may indicate that further testing is necessary, such as a sleep study to determine if CPAP might help keep your airways open to better oxygenate. The test may also be used to show how well your lungs are responding to treatment over time.

Conclusion. It’s true that PFT testing can really tire you out. Now you understand why the test is so important, and why you should put in your best effort. The results can help your doctor diagnose and treat your disease, helping you to live better with it.

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John Bottrell
Meet Our Writer
John Bottrell

John Bottrell is a registered Respiratory Therapist. He wrote for HealthCentral as a health professional for Asthma and Chronic Obstructive Pulmonary Disease (COPD).