Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Portable AP upright chest radiograph obtained . Lung volumes are low . Midline sternotomy wires and mediastinal clips are noted . There is bibasilar atelectasis without clear signs of pneumonia or CHF . No large effusion is seen . Heart size is normal . Mediastinal contours are unremarkable . Bony structures are intact . No free air below the right hemidiaphragm .
    OUTPUT:
    
Mild bibasilar atelectasis . Evidence of prior CABG . Otherwise , normal .