Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Again seen are changes of median sternotomy , mediastinal clips , and coronary artery bypass grafting . Lung volumes remain low , with increasing discoid atelectasis in the left lower lobe . There is mild central venous congestion . Small bilateral pleural effusions , right greater than left . No pneumothorax . Heart size is top normal .
    OUTPUT:
    
Limited study . Low lung volumes and small effusions .