Pulmonary function tests are the tests performed to determine the efficacy of the functioning of the lungs. In this test, the patient is asked to blow air into a tube-like device and the readings are generated on a monitor. A proper interpretation of the graph is done to assess the lung’s volume, capacity, flow rate and extent of gas exchange. PFT is also used for the following purposes: To know the response of the treatment. Screening the presence of obstructive and restrictive disease. Examination of patients before the surgery.