Any scuba diver is aware of the dangers of decompression. When you dive deep in high pressure water, the air which you breathe from your tank will have the same pressure that the water is exerting. If this were not the case then the air wouldn’t come out of your tank. At a depth of 33 feet the air pressure is twice that of atmospheric air pressure on land.
High pressure nitrogen from this air dissolves in your bloodstream and water in your body. Anyone who had unscrewed a lid on a shaken fizzy drink bottle knows that bubbles start to fizz up due to the lessening of pressure. The same effect happens to the nitrogen in the bloodstream of a diver if they ascend too quickly.
So, how do whales and other marine mammals handle this tremendous pressure increase? They have adapted to collapse their thoracic cavity, lungs, and alveolar sacs. Whales have very weak and flexible rib cages. While diving, the thoracic cavity is collapsed so no air can get in. When this collapse occurs, there is still air with high nitrogen levels present, in the alveolar sac, which is the site of gas exchange. Marine mammals have adapted to this by creating a cartilage build up in the bronchioles. This allows for alveolar collapse and storage of the air in the bronchioles. This is important because nitrogen is no longer at the site of gas exchange and cannot be absorbed into the body.
Therefore the nitrogen will not fizz in their bloodstream upon ascent, therefore making them effectively immune to the bends.