The term "spirometry" is derived from the Latin words SPIRO (to breathe) and METER (to measure). Simply put, spirometry is the measurement of how much (volume) and how fast (flow rate) somebody can exhale. Spirometry is a non-invasive and completely painless procedure which only takes a few minutes to perform. Otherwise known as the forced vital capacity test (FVC), the patient first inhales maximally, then exhales into a spirometer as fast and long as possible. Spirometry is "effort-dependent", which means it is very important for the patient to give their best effort in order for the results to be useful.
The FVC and the FEV1 are the two most important measurements in spirometry. The FVC represents the total amount of air that the patient exhaled. The FEV1 (forced expiratory volume in 1 second) is the total amount of air exhaled during the first second of the test. These and other spirometry measurements are compared to what is predicted normal based on the patients age, height, sex, and race. Age plays an important role as maximum lung growth appears in the 20s or 30s, after which a slow decline in the FVC and FEV1 occurs throughout adulthood. Height also plays an important role; consequently it can be beneficial to measure height as opposed to simply inputting the subjects declared height.
It is often beneficial to perform two or more efforts in order to get the best possible results from the patient. Upon completion of the test, the spirometer should provide a report that compares the measured results to predicted normals, provide the percent of normal, an interpretation and at least a time vs. volume or flow vs. volume graph. In general, if the patients FVC and FEV1 results are ≥ 80% of predicted normal, they are considered to have normal lung function. However, your physician will assist in making that determination.
Spirometry plays a key role in asthma and COPD. First it is necessary for confirming the diagnosis. Second, the spirometry results are used to identify the severity or "stage" of the disease which determines appropriate treatment, and third, to determine the improvement or response to the treatment.