What is Pulmonary Function Testing?
Some call it pulmonary function testing, or a PFT. Some call it spirometry. No matter what you refer to it as it entails a series of breathing tests. The Global Initiative for COPD (GOLD) has new COPD guidelines. Here’s what they now say about PFTs.
What is a PFT?
The guidelines say that a PFT is “required” to make a COPD diagnosis. It should only be ordered if you are experiencing COPD symptoms. It entails working with a technician, such as a respiratory therapist. You place your mouth over a mouthpiece. A clip will be placed over your nose. Then you perform a series of breathing tests. The results can help your doctor rule in or rule out COPD. After the test, you will be given an albuterol breathing treatment. You will then rest for about ten minutes. Then you will repeat the tests.
What is an FVC?
The most important test is called a forced vital capacity (FVC). This is where you take in as deep a breath as you can. Then, you exhale as fast as you can. You keep exhaling until you have no breath left. Then you breathe normally. Then you rest.
What does this show?
The computer will draw out a flow volume loop. This will show if you have normal lungs. It will also show if you have obstructed airways.You can see this by the picture above. The dotted line shows a normal flow volume loop for this person. The solid line shows airflow obstruction. This is sometimes referred to as airflow limitation. This is because airway obstructions can slow the speed of air as you exhale. This is a classic sign of COPD. But, this alone cannot diagnose COPD. This is where computer calculations come in handy.
What calculations does the computer make?
The computer will calculate numbers or percentages that are valuable. These include.
- TLC. Total lung capacity. This is the total amount of air that stays in your lungs after a complete exhalation. Emphysema causes air to become trapped in your lungs. So, TLC will be increased. With bronchitis, TLC will be normal or decreased.
- FVC. This shows the total amount of air you can exhale in one breath after a full inspiration. People with COPD will have less air to blow out. So, this number will usually be decreased.
- FEV1. This is forced expiratory volume. It’s the amount of air that you exhaled in the first second. It is the most valuable number obtained. Normal is 80% or better. It’s usually decreased if you have COPD. It can be used to measure how severe your COPD is.
- Between 50-79% is moderate COPD
- Between 30-49% is severe COPD
- Less than 30% is very severe COPD
There is a note here in the guidelines. It says that “there is a weak correlation between FEV1, symptoms, and impairment of a patient’s health status. For this reason, formal symptomatic assessment is required.”
I think this was put in there because sometimes a PFT may show severe COPD. But, the patient may not present as a severe COPDer. This is to make sure that doctors look at the whole patient, and not just the number.
FEV1/ FVC. This is a calculation that is very sensitive. It can show if you have airflow limitation. This is a key criterion for diagnosing COPD. If this value remains less than 70% after inhaling albuterol, a diagnosis of COPD MAY be made.
It should be noted here that there is no one test to define COPD.
But, this seems to be the best one, especially if you’re also having COPD symptoms.
Should you have repeat PFTs?
Older guidelines recommended occasional PFTs to monitor the effectiveness of treatment over time. If necessary, treatment could be adjusted. But, this is no longer recommended. The new guidelines just recommend the one test for diagnosing COPD. This is nice because it can be hard to do PFTs when you have COPD.
What to make of this?
So, the COPD guidelines recommend a PFT for diagnosing COPD. Sure, it can be a difficult test to perform when you have COPD. But, the results can help doctors get you a proper diagnosis. Then your doctor can discuss with you best treatment options. This is all in an attempt to help you live better and longer with COPD.
- Global Initiative for Chronic Obstructive Lung Disease. Global Strategy for Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease, 2017, pages 24-31, file:///home/chronos/u-8cb586a83dc43daeeeecf6141dd804bfbc193ecf/Downloads/wms-GOLD-2017-FINAL%20(3).pdf, accessed 12/22/17