They also exchange a greater percentage of lung air with each breath up to 80 percent of the lungs' contents, compared with 30 percent in humans. Unlike a seal, which exhales before diving, a whale inhales before diving, taking down at least partially inflated lungs. Surprisingly, the lungs of a whale are not significantly larger than those of land mammals, and the ratio of lung volume to body size is actually smaller than that of land mammals. In fact, the deepest diving whales have the smallest lungs. As the whale dives, its flexible lungs collapse, forcing air into the windpipe and nasal ducts, where internal body surfaces can't absorb nitrogen.
Research indicates that cetaceans can tolerate higher nitrogen concentrations than humans can.
How this works is unclear, but it may be related to differences in body chemistry. Instead of developing larger lungs, whales have developed a modified circulatory system. Whales have more red blood cells the cells that carry oxygen than humans, and the hemoglobin concentration in the blood is generally higher than in land mammals. This increases the amount of oxygen the blood can carry. Likewise, the muscle tissue of toothed whales has a higher concentration of the oxygen-binding protein myoglobin.