Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes remain low . Atelectasis at the left base is improving . There is no new focal airspace opacity . There is no pleural effusion or pneumothorax . The heart is top normal . Mediastinal hilar contours are normal .
    OUTPUT:
    
Persistently low lung volumes . Improving opacification of the left base may reflect improving atelectasis . There is no new focal opacity .