Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest provided . Midline sternotomy wires and mediastinal clips are again noted . Persistent atelectasis in the left lower lobe is seen , slightly improved from the prior exam . The right lung is clear . Cardiomediastinal silhouette is unchanged . Bony structures are intact .
    OUTPUT:
    
Persistent left basal atelectasis . No acute intrathoracic process .