atelectasis

n. (Medicine) collapse of the lungs

Atelectasis is defined as a state in which the lung, in whole or in part, is collapsed or without air. It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.  Infant respiratory distress syndrome includes another type of atelectasis, and is described and discussed in its own article.
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Atelectasis is a collapse of lung tissue affecting part or all of one lung. This condition prevents normal oxygen absoption [more]Atelectasis - Community and Resources

Noun
1. collapse of an expanded lung (especially in infants); also failure of pulmonary alveoli to expand at birth
(hypernym) pathology

noun
collapse of a lung, where the lung fails to expand properly