Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP portable semi-upright view of the chest . Sternotomy wires and prosthetic valves are unchanged . Low lung volumes . Trace bilateral pleural effusions are unchanged . Bibasilar atelectasis . Vascular stent projects over the region of the right subclavian / brachiocephalic vein . Unchanged retrocardiac opacity .
    OUTPUT:
    
Low lung volumes . Unchanged retrocardiac opacity , this may represent atelectasis however infection can not be ruled out . No pneumothorax .