You might mistakenly think you are looking at blood vessels when you examine parts of the circulatory systems of dolphins and whales. These cetaceans have especially dense, complex networks of blood vessels mainly associated with the brain and spine, but scientists didn’t know why. A new analysis has shown that the networks protect cetaceans’ brainsResearchers report in the Sept. 23rd on the pulses and blood pressure of the animals while deep under the sea. Science.
Whales and dolphins “have gone through these really amazing vascular adaptations to support their brain,” says Ashley Blawas, a marine scientist at the Duke University Marine Lab in Beaufort, N.C., who was not involved with the research.
Called retia mirabilia, which means “wonderful nets,” the blood vessel networks are present in some other animals besides cetaceans, including giraffes and horses. But the networks aren’t found in other aquatic vertebrates that move differently from whales, such as seals. So scientists had suspected that the cetaceans’ retia mirabilia play a role in controlling blood pressure surges.
Whales and dolphins dive by moving their tails up and down, creating blood pressure surges. Similar surges in blood pressure can also be experienced by land animals like horses galloping, which can exhale some of the pressure. Some cetaceans, however, hold their breath to release some of the pressure. For long periods, you can dive (SN: 9/23/20). These blasts could cause blood vessel damage and even death if there is no way to release the pressure.
In the new study, biomechanics researcher Margo Lillie of the University of British Columbia in Vancouver and colleagues used data on the morphology of 11 cetacean species to create a computational model that can simulate the animals’ retia mirabilia. It was found that the arteries as well as veins within this maze of blood vessels are very close, and sometimes even joined. Accordingly, the retia Mirabilia could help equalize the difference in blood pressure caused by diving. This could be done by redistributing blood pulses from veins to arteries and vice versa. These networks are able to eliminate, or at the very least, weaken, large blood pressure spikes that could otherwise reach the brain and cause havoc.
The networks “equalize the [blood flow] in a way that you never lose that blood that’s in the vein and it doesn’t collapse down on itself, and you don’t have that shooting arterial blood going really fast into the brain,” says marine biologist Tiffany Keenan of the University of North Carolina Wilmington who was not involved in the study. “It’s really neat to know what we’ve always wondered, but no one had been able to show.”
However, it can be difficult to study cetaceans because of their protected status and restricted access to samples. These samples are usually from animals who have been stranded. Researchers agree. To make the model, researchers had to enter data from several species.
“They take a little bit from here and a little bit from there, mixing a dolphin with a beluga whale with a beaked whale — it is sort of like a quilt,” says Andreas Fahlman, a marine scientist at the Oceanogràfic Foundation in Valencia, Spain, who was not involved in the study.
The model might not reflect the unique characteristics of other species. Different anatomies can cause divergence in movement and movements. Some species may stay closer to the surface while others dive deeper. The computational model may not accurately reflect real-life dynamics if we take a closer look at dolphins and whales’ circulatory systems.
