While formal pulmonary function testing is not often (if ever) performed in the ED, many patients with a history of COPD, asthma, CHF, sarcoidosis, etc, have had pulmonary function testing performed in the past.  Having an understanding of the underlying pathophysiology of these conditions, physiology of the lungs and respiration, and understanding of how the testing is performed is critical to being able to appropriately interpret the results of these test and apply the test results to our patients.