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Pulmonary Function Tests - Spirometry
So, you’ve been told you have to have a Pulmonary Function Test or a Spirometry Test to check and see if you have COPD and to what extent. These tests are usually performed in a respiratory function lab by qualified technicians who will guide you through them. The tests will check your air-flow, your lung volumes and your gas diffusion levels. They may or may not include an arterial blood gas test. We will be referring to the sample PFT below which is an actual PFT done at the QEII Respiratory Lab in Halifax, Nova Scotia. (Note: the Numbers in Blue are not part of the lab print out They are intended as reference to explain what they mean below)
We'll start with Spirometry:
Disclaimer: The information below is far from all inclusive. Additionally it has NOT been reviewed by a Dr. It is intended solely for basic information purposes only.
Spirometry: This is one test that can also be performed in the doctor’s office if the doctor is so equipped or an asthma clinic. It’s a shorter, simpler version of a PFT and though it doesn’t give as “complete” a picture as the PFT, it can accurately tell a) whether you have COPD, b)whether there’s a reversible component as in asthma and c) at approx. what stage you are with COPD.
Spirometry: For this portion/test, reference everything ABOVE the Lung Volume. (This is usually the only values recorded on a Spirometry test) – Also; we will only be addressing the more important or significant numbers that many COPD patients are interested in.
Spirometry:
Before you take your test, you will be asked specific questions. The most important questions deal with your age, height and sex. From this information, a reference (ref) (column #7) or predicted number is determined. Your results are measured against these numbers.
#1 FVC - Forced Vital Capacity - the volume of air which can be forcibly and maximally exhaled out of the lungs until no more can be expired. It is usually measured in liters.
#2 FEV1 - Forced Expiation Value after 1 second - the volume of air which can be forcibly exhaled from the lungs in the first second of a forced expiratory maneuver. It too is measured in liters.
#3 FEV1/FVC - Forced Expiration Value after 1 second as a Percentage of Forved Vital Capacity- indicates what percentage of the total FVC was expelled from the lungs during the first second of forced exhalation.
Of these three, FEV1% is the one used by most COPD’ers to express their lung function. (Fig.1 – line #2 – column #12). When combined with your BMI (body mass index) and your "functional" dyspnea (shortness of breath) collectively, this is what indicates what "stage" you are in. The standard below is what's been established by GOLD (Global Initiative for Obstructive Lung Disease)
Stage Degree FEV1%
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I |
Mild |
≥ 80% of Predicted |
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II |
Moderate |
50-80% of Predicted |
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III |
Severe |
30-50% of Predicted |
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IV |
Very Severe |
Less than 30% of Predicted or Less than 50% with Chronic Respiratory Failure |
You will see Pre (#9) and Post (#11). The first time you take this test, you will establish a value for FEV1. This is your Pre-bronchodilator or inhaler value. You will then be given some puffs of a fast-acting inhaler and after twenty minutes you will take the test again. These results are your post-bronchodilator values and the difference between Pre and Post are recorded. If your Post value of FEV1 is greater than 15%, you are considered to have an asthma component which can be reversed by inhalers. (In subsequent PFT’s or Spirometry tests you will probably not do a Pre and Post if it’s known that you do not have an Asthma component. You will see only Post results.)
Column (#10) gives us the % of predicated value before bronchodilator use. Column (#12) gives us the % of predicated value after bronchodilator use.
Column (#13) records the percentage change between Pre and Post values.
This way to Understanding a FULL PFT (Pulmonary Function Test)
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