Atelectasis in the new-born is the abnormal persistence of the condition of incomplete expansion of the lungs which is physiologic in the first few days of life. The lungs of the fetus are completely atelectatic. With the onset of respiration expansion begins, but, as pointed out by Wasson,1 in most cases it probably does not become complete for several days. A certain amount of atelectasis is physiologic, therefore, during the first few days of life, but ordinarily does not cause symptoms. When it is sufficiently extensive to cause symptoms, it must be regarded as pathologic.
In cases of atelectasis in the new-born, failure of proper functioning of the respiratory center is generally held to be the most frequent cause of abnormal persistence of the fetal state in some parts of the lungs. Often the cause of the failure of the respiratory center cannot be determined, but immaturity, asphyxia, hemorrhage
DUNHAM EC. ATELECTASIS IN THE NEW-BORN. Am J Dis Child. 1932;43(3):594–603. doi:10.1001/archpedi.1932.01950030064009