Spirometry is a pulmonary function test. During the procedure, the patient is asked to inhale and exhale using a mouthpiece connected to the spirometer. After breathing in deeply, the patient must breathe out with the maximum energy and speed they can manage. The spirometer measures the volume of air inhaled and the flow speed; test results are displayed on a screen. Spirometry is a useful tool for the diagnosis of lung conditions like bronchial asthma, chronic cough and pulmonary function decline in smokers.