Pulmonary function tests are performed for a variety of purposes and are particularly important for physical health, including the following: 1) qualitative and quantitative assessment of the subject’s respiratory physiology; 2) diagnosis of the lungs and airways in the early stages of some diseases; 3) assessment of the function of the small airways in patients who have been smoking for a long time; 4) physical examination of healthy patients, including tests of respiratory function; 5) assessment of critically ill patients, those requiring surgery, the risk of postoperative anesthesia and the severity of the postoperative gain.