These models were created from 3d medical images of a champion free-diver http://en.wikipedia.org/wiki/Free-diving ie someone who can hold their breath for a very long time.
The unpacked model shows the normal lung capacity of about 4.6L. The packed model shows a technique to force air into the lungs that increased the capacity to 11.9L.
Both models were created from the same person and are proportionally correct.
As a guide orientation the lungs are very close to each other at the front and are separated by the spine at the back
The files are quite large because they are the direct output of the image segmentation program. Any smoothing I tried did bad things to the sharp edges where the two halves join.
Print each half of the model and glue together. I used an infill of 15% and the packed lungs took about 7 hours to print.
Use a mixture of abs and acetone to both fill in holes and give a nice shiny finnish.