Spirometry, the measuring of breath, consists of a wide array of Pulmonary Function Tests (PFTs). Each PFT is typically titled with an abbreviation that, to anyone outside – or only recently involved in – the world of pulmonary pathology, can be difficult to discern to the point of seeming deliberately infuriating and, perhaps, obfuscating.
However, like any other area, if we’re going to talk about lung-function we need a standardized lexicon and a methodology for interpreting the results.
Hopefully the following can help explain.
| Abbreviation | What it stands for | What it measures | Metrics used |
|---|---|---|---|
| FVC | Forced Vital Capacity | The amount of air exhaled from full inspiration to full expiration. | Liters, Percentage |
| FEV1 | Forced Expiatory Volume in the 1st Second | The volume of air exhaled in the first second. | Liters, Percentage |
| FEV1/FVC | Of the total amount of air exhaled (FVC), the percentage exhaled in the first second. | Percentage | |
| FEV6 | Forced Expiatory Volume in 6 seconds | The volume of air exhaled in 6 seconds. | Liters, Percentage |
| FEF25-75% | Forced Expiatory Flow over the middle half of the FVC | The average flow from the point that the FVC is 25% complete to the point that the FVC is 75% complete. | Liters per second, Percentage |
| PEF | Peak Expiatory Flow | The rate at which the patient exhales. | Liters per second, Percentage |
| VC | Vital Capacity | The amount of air the patient’s lungs can hold. | Liters, Percentage |
| ERV | Expiatory Reserve Volume | The maximum amount of air exhaled beyond the end of expiration. | Liters, Percentage |
Note
Most PFT metrics are given as a percentage. This percentage results from the comparison of the patient’s PFT with the results of those of other healthy patients who are of similar age, gender, height and weight. So if you’ve ever watched ER or Grey’s Anatomy and heard a doctor say that a patient has only a 15% lung capacity, what the doctor means is that compared to a patient of the same age, gender, height and weight, the patient’s lungs are functioning at 15% of what is expected.
It’s also important to note that since the results are given as a comparison it is entirely possible for a PFT to come in at higher than 100%. If a patient’s FEV1 is expected to be 3.18 liters and she manages 3.50 liters, her FEV1 will come up as 110%. Rather than being a flaw in the system of PFT metrics, it simply means that the patient performed ten percent better than expected. This is a good thing.
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