A 15-month-old baby is brought to the ER dyspneic, coughing,…

A 15-month-old baby is brought to the ER dyspneic, coughing, and displaying wheezes audible to the unaided ear. Chest x-rays reveal a slight rightward mediastinal and cardiac shift and over aeration of the left lower lobe. A left-lateral decubitus view indicates that the left lower lobe remains more inflated than the left upper lobe. What problem is this child likely experiencing?