Pulmonary Function Test (PFT) - Understanding

A PFT is a more "in-depth" Spirometry Test.  For this test we will be referencing ALL of the numbers shown in blue on the sample test below.

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. 

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 Expiration 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 Forced 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). This is the value that establishes what stage of COPD we are in. The standard  being used below  is the GOLD (Global Initiative for Obstructive Pulmonary Disease) standard.

                Stage                                     Degree                                    FEV1%

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. (before & after the bronchodilator)

Column (#14) is used by the technician for any added comments.

2nd Portion:  Lung Volumes

Lung volume measurement can be performed in two ways. The most accurate way is for a person to sit in a body plethysmograph (aka a body box), a sealed, transparent box that resembles a telephone booth, while breathing in and out  into a mouthpiece.

Changes in pressure inside the box allow determination of the lung volume. Lung volume can also be  measured when a person breathes nitrogen or helium gas through a tube for a specified period of time. The concentration of the gas in a chamber attached to the tube is measured, allowing estimation of the lung volume.

#4 TLC - The volume of gas contained in the lung at the end of maximal inspiration.

#5 RV - The amount of air left in the lungs after a maximal exhalation.

3rd Portion: Diffusing Capacity:

The diffusion capacity is measured when a person breathes carbon monoxide for a very short time, often one breath. The concentration of carbon monoxide in exhaled air is then measured. The difference in the amount of carbon monoxide inhaled and the amount exhaled allows estimation of how rapidly gas can travel from the lungs into the blood.

#6 DLCO – This is the measurement of  the lungs ability to add oxygen to the blood and extract carbon dioxide from the lungs. The lower the DLCO value, the more likely you will become short of breath during exertion.

Summary

This has been a very quick and simple overview of what most of us consider a PFT to be. There are other Pulmonary Function Tests but they are usually done apart from the “Breathing Test”. The items we touched on are those that we as COPD’ers most often refer to. The other items on the sample test are used by the medical community to refine their diagnoses. If you wish to learn the other terms, simply search the web for “Pulmonary Function Tests used in COPD”. You will find a myriad of sites.

Remember: Be sure to request a copy of your test and keep it for your own records  

Saturday January 09, 2010