Complex sentence: Spirometry (meaning "the measuring of breath") is the most common of the pulmonary function tests (PFTs), measuring lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.
Split into simpler sentences: 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.