If a human dived to the depth of a whale, our lungs would shrink, which would cause the capillaries in them to burst. Also the rib cage would collapse and crush the lungs. Whales however have both collapsable lungs and ribs. They're ribs are made of stretchy cartalidge, and have only a few 'true' ribs made of bone stretching across the whole chest. Their lungs are able to compress without the cappillaries bursting.