Spirometry is one of the common Pulmonary function tests for t he purpose of measuring the lung function, particularly it is used to measure the amount and speed of air that can be exhaled or inhaled.  The American Thoracic Society and the European respiratory society set most commonly used guidelines for spirometric testing and interpretation. Basically the Spirometry is an important tool used to assess the conditions such as asthma. So for the purpose of assessing or diagnosing asthma through Spirometry a device known Spirometre is used in which patient places his or her lips around the blue mouthpiece. There is a nose clip used that guarantees that the breath will flow only through the mouth.

The Spirometer, which is used to assess asthma, comes in several different varieties and these Sprirometer display the graph called Spirograms. The graph can be a Volume –time curve that shows the volume along the Y-axis and time along the X-axis another is flow-volume loop that graphically depicts the rate of inflow on the Y-axis and the total volume inspired or expired on the X-axis. In the process the patient is asked to take the deepest breath, they can then exhale in to the sensor. During the test, the nose clips might be used to prevent air escaping through the nose and asses the possible airway obstruction and the severity of the asthma as well.