Spirometry is a painless diagnostic test that measures the volume and flow rate of air into the lungs. It is done through a specialized apparatus, a spirometer or pneumotachograph, whose nozzle must place the patient's lips, while leading tweezers placed in the nose to prevent air from escaping that way. With this test three measurements are made and the best result of the three is the one deck to patient assessment. There are two types of spirometry: simple spirometry and spirometry. In the first patient, after a maximal inspiration, eject the entire volume of air that is able, using all the time you need requested. In spirometry, however, the patient expels all the air in your lungs containing after a deep inspiration in the shortest possible time. The information is obtained from each of these stress tests is different and usually do consecutively. This technique is used for early diagnosis of chronic obstructive pulmonary disease (COPD) or to control the evolution of already treated patients.