The Lung

ATELECTASIS (COLLAPSE) is loss of lung volume caused by inadequate expansion of airspaces; this leads to shunting of inadequately oxygenated blood from pulmonary arteries into veins, thus giving rise to hypoxia. Pathogenetically atelectasis is classified into three forms 1. Resorption atelectasis complicating obstruction. The air already present distally gradually becomes absorbed, and alveolar collapse follows. Depending on the level of airway obstruction, an entire lung, a complete lobe, or a segment may be involved. A mucous or muco-purulent plug is the most common cause of such obstruction for e.g. following surgical operations or bronchial asthma, bronchiectasis, chronic bronchitis, or the aspiration of foreign bodies, particularly in children. 2. Compression atelectasis is usually due to mechanical compression of the lung by pleural distension as in pleural effusion (congestive heart failure) or pneumothorax. Basal atelectasis is another example & is due to elevated diaphragm as that occurs in bedridden patients, in those with ascites, and during and after surgery. 3. Contraction atelectasis occurs in the presence of focal or generalized pulmonary fibrosis or pleural fibrosis; in these situations there is interference with expansion and an increase in elastic recoil during expiration. Atelectasis (except contraction type) is reversible and should be treated quickly to prevent hypoxemia and infection of the collapsed lung.