Spirometry is a technique or perform simple, painless test that measures the capacity of our lungs take in and release air. Used to diagnose some of the more common obstructive lung disease (asthma, cystic fibrosis ...), or other breathing difficulties expressed by some patients and for which the cause is unknown. Furthermore, it is also used to evaluate whether exposure to allergens causes some damage to our respiratory system, in cases of patients with allergies. For its realization a spirometer is used and there are two levels or types of respiratory function tests: the first, the patient should inspire everything you can and quickly and then expel all the air in the time you need; The second way to do this test requires the patient to perform a slow but continuous inspiration and after a quick and forced expiration, allowing expel all the air in your lungs.