Pulmonary function tests measure oxygen volumes and flows, and how well oxygen diffuses into the blood. The same test can be performed measuring metabolic capacities while a patient is at rest and with exercise.
Patients should try and omit any inhaled medicines the day of the test. Fasting is only necessary for metabolic tests (indirect calorimetry), but a full meal just prior to testing should be avoided. Wear comfortable clothing and shoes.
Pulmonary function tests are commonly done while sitting in a glass booth, but only one short test is done with the doors closed. You'll be asked to breath in different manners to measure your capacities. These tests take about 30-60 minutes. Sometimes tests are repeated after an inhaler to see if there is improvement. Calorimetry is done while resting, lying under a clear canopy, for 15 minutes.