An individual breathes in and forcefully exhales through a mouthpiece. One's specific measurements are compared to measurements healthy people of the same race, age, gender, height and weight.
Clinical Pulmonary Function Testing, Exercise Testing, and Disability Evaluation. In Chest Medicine: Essentials Of Pulmonary And Critical Care Medicine. Editors: Ronald B. George, Richard W. Light, Richard A. Matthay, Michael A. Matthay. May 2005, 5th edition.