Obstructive atelectasis
Obstructive atelectasis is the most common type and results from reabsorption of gas from the alveoli when communication between the alveoli and the trachea is obstructed. The obstruction can occur at the level of the larger or smaller bronchus. Causes of obstructive atelectasis include foreign body, tumor, and mucous plugging. The rate at which atelectasis develops and the extent of atelectasis depend on several factors, including the extent of collateral ventilation that is present and the composition of inspired gas. Obstruction of a lobar bronchus is likely to produce lobar atelectasis; obstruction of a segmental bronchus is likely to produce segmental atelectasis. Because of the collateral ventilation within a lobe or between segments, the pattern of atelectasis often depends on collateral ventilation, which is provided by the pores of Kohn and the canals of Lambert.