PFT
Meaning of PFT: No single number carries the answer here; the finding lives in the relationship between the measurements taken together.
Definition of PFT
PFT stands for pulmonary function test, a group of breathing measurements describing how well the lungs move and exchange air. A person breathes through a mouthpiece into a device that records how much air the lungs hold, how fast that air can be blown out, and how readily gas crosses from the air sacs into the bloodstream.
What is measured?
| Measurement | What it captures |
|---|---|
| Spirometry | The total volume blown out in one forced breath, and the portion of it delivered in the first second |
| Lung volumes | Total capacity, and the air still left in the chest after breathing all the way out |
| Diffusing capacity | How readily a trace gas crosses from the air sacs into the blood |
| Bronchodilator response | Spirometry repeated after an inhaled reliever, to see whether narrowing reverses |
Spirometry is done at the mouth and depends on maximal effort, so it is coached and repeated until the results agree. Lung volumes need either a sealed booth or the dilution of an inert gas, because air trapped behind narrowed airways cannot be blown out and so cannot be measured directly.
How do obstructive and restrictive patterns differ?
In an obstructive pattern the airways are narrowed, so air leaves slowly. The share of the vital capacity delivered in the first second falls, air is left behind after each breath, and total lung volume may actually rise as the chest becomes over-inflated. Asthma, chronic obstructive pulmonary disease, emphysema and bronchiectasis produce this picture. In a restrictive pattern the lungs or the chest cannot expand fully, so total volume falls while the flow proportion stays normal or even rises. Scarring of lung tissue, chest wall or spinal deformity, weak breathing muscles and severe obesity produce it. Diffusing capacity separates the causes further, falling where the air sacs or their blood supply are damaged and staying normal where the limitation is mechanical. Mixed patterns are common and are read as a whole.
What is the testing used for?
It identifies whether a pulmonary problem exists and which kind, tracks a known lung disease over time so that a change in symptoms can be matched against a change in function, assesses breathlessness with no obvious explanation, and provides a baseline before an operation or before treatment with a drug known to injure the lungs. Results are compared against reference values for age, height and sex rather than a single fixed threshold. Because the test measures mechanics, it does not by itself show how much oxygen is reaching the blood during ordinary activity, which is measured separately.
Also known as
Used in a sentence
Pulmonary function testing was ordered to evaluate the patient's persistent shortness of breath.
Good to know
PFT results are read as a pattern rather than as a single number, since the combination of values separates an obstructive process, which narrows the airways, from a restrictive one, which limits how fully the lungs expand.