Forced Expiratory Volume In 1 Second FEV1 marker
«Spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time.
Spirometry generates pneumotachographs, which are charts that plot the volume and flow of air coming in and out of the lung from one inhalation and one exhalation.» (wikipedia)