Lung function tests are often performed when a patient experiences shortness of breath or other issues with their breathing in order to help diagnose certain respiratory conditions ranging from asthma to COPD, mesothelioma and pulmonary fibrosis. They may also be employed to determine the degree to which a patient’s lungs have been affected by a chronic respiratory condition. One of the most common lung function tests employed by primary care and specialty physicians is called spirometry. This test requires the patient to blow (both calmly and forcefully as directed) into a mouthpiece that is connected to a special recording device that measures how much air you can take in and expel and at what rate over a certain amount of time. Other lung function tests measure the volume of the lungs and their diffusion capacity, or ability to exchange gases.