A Spirometer is made with an inert gas that has a known volume and concentration; it commonly contains 10% helium. The airway is connected to this closed system by turning a valve during end-tidal exhale while the individual is breathing through a mouthpiece with their nose taped. The gas in the subject's lung equilibrates with the gas in the Spirometer over the period of a few minutes, and the constantly measured helium concentration decreases to a new, lower steady-state level. A modest flow of oxygen is given to the closed system to make up for the subject's continued oxygen consumption while maintaining the volume of the mixing chamber or spirometer.
Carbon dioxide is eliminated from the closed system by soda lime absorption. Calculating the unknown volume (FRC) delivered to the system is possible using the ratio of the beginning to final concentration of helium. Calculating the subdivisions of lung volume and making adjustments for any deviation from the relaxed FRC at the time the valve was opened to begin the test are both made possible by a continuous tracing of the spirogram that includes a maximum inspiratory and expiratory effort.
Discover More- http://latestcmiblogs.weebly.com/article/a-spirometer-aids-in-measuring-the-amount-of-air-breathed-in-and-out
