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Etymology: L, passivus + expirare, to breathe out
normal exhalation that occurs without direct muscular effort, as during normal tidal breathing. Air is expelled from the lungs as a result of the recoil effect of elastic tissues in the chest, lungs, and diaphragm.
Expiration, performed during quiet respiration, that requires no muscular effort. It is brought about by the elasticity of the lungs, and by the ascent of the diaphragm and the weight of the descending chest wall, which compress the lungs.
See also: expiration