Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: As compared to prior study of ___ , cardiomediastinal contours are stable . Lung volumes are lower , and the left hemidiaphragm contour appears less distinct on the lateral view compared to the previous exam . Saber sheath trachea configuration is consistent with provided history of COPD .
    OUTPUT:
    
Limited study due to low lung volumes . Repeat lateral radiograph with improved technique may be helpful to exclude the possibility of an early pneumonia at the left lung base .