Asked by: Eleanor Caldwell, London
In scuba divers, the bends is caused by ascending too quickly. Nitrogen dissolved in the bloodstream can form bubbles before the gas has had time to return to the lungs, causing pain and tissue damage. Marine animals, however, don’t normally suffer from this condition.
To find out why, scientists recently put a dead dolphin and seal in a pressurised chamber and carried out a CT scan. They found that the marine mammals’ lungs were separated into two regions: one filled with air, one collapsed. As the lung is collapsed, so too are the little air sacs inside the lung, where gas exchange takes place. It’s thought that the blood flows mostly through the collapsed part of the lung, minimising the amount of nitrogen that can enter the animal’s bloodstream, while still allowing some oxygen and carbon dioxide to pass.