Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Patient is status post previous median sternotomy and coronary artery bypass surgery . Lung volumes are low . Allowing for this factor , cardiomediastinal contours are probably stable , but difficult to compare due to differing inspiratory levels between the exams . The relatively low lung volumes results in crowding of bronchovascular structures at the lung bases , but no confluent areas of consolidation are evident , and there are no definite pleural effusions . Left hemidiaphragm remains moderately elevated .
    OUTPUT:
    
Low lung volumes with minor bibasilar atelectasis but no findings to suggest acute pneumonia . If symptoms persist , repeat chest radiograph with improved inspiratory level may be helpful for more complete evaluation of the lungs . Chronic elevation of left hemidiaphragm .