Abstract: Pulmonary atelectasis refers to a constricted and airless state of the whole or part of the lung. Pulmonary atelectasis may be acute or chronic, and in chronic atelectasis lesions there is often a combination of pulmonary atelectasis, infection, bronchiectasis, tissue destruction, and fibrosis. Pulmonary atelectasis is strictly speaking a condition in which the lungs have never been filled with gas since birth, and the loss of gas in inflated lung tissue (de-aeration) is referred to as pulmonarycollapse. However, due to the customary use over the years, atelectasis in the broad sense can include congenital atelectasis and acquired pulmonary atrophy.