If you look at parts of the circulatory system of whales and dolphins, you might think you’re looking at a Jackson Pollock painting, not blood vessels. These cetaceans have complex and especially dense networks of blood vessels associated primarily with the brain and spine, but scientists didn’t know why. A new analysis suggests that nets protect cetacean brains of blood pressure pulses endured by animals as they dive to the deep ocean, researchers report in the Sept. 23 issue Sciences.
Whales and dolphins “have gone through these really amazing vascular adaptations to support their brains,” says Ashley Blawas, a marine scientist at the Duke University Marine Laboratory in Beaufort, North Carolina, who was not involved in the research.
Called retia mirabilia, meaning “wonderful networks,” the networks of blood vessels are present in a few other animals besides cetaceans, including giraffes and horses. But the webs are not found in other aquatic vertebrates that move differently from whales, such as seals. So scientists had suspected that the cetacean’s retia mirabilia plays a role in controlling blood pressure surges.
When whales and dolphins dive, they move their tails up and down in an undulating fashion, creating sudden spikes in blood pressure. Land animals that experience similar surges, such as galloping horses, can release some of this pressure by exhaling. But some cetaceans hold their breath to diving for long periods of time (Serial number: 09/23/20). Without a way to relieve that pressure, those blasts could tear blood vessels and damage other organs, including the brain.
In the new study, biomechanics researcher Margo Lillie of the University of British Columbia in Vancouver and her colleagues used data on the morphology of 11 cetacean species to create a computational model that can simulate the animals’ retia mirabilia. She revealed that the arteries and veins in this tangle of blood vessels are very close together and can sometimes even be joined. As a result, retia mirabilia could even out differences in blood pressure generated by diving, perhaps by redistributing pulses of blood from arteries to veins and vice versa. In this way, the networks eliminate, or at least weaken, the large surges in blood pressure that could otherwise reach and devastate the brain.
Networks “equalize [blood flow] in a way where you never lose that blood that’s in the vein and it doesn’t collapse on itself, and you don’t have that arterial blood shooting out that goes really fast to the brain,” says marine biologist Tiffany Keenan of the University of North Carolina Wilmington, who was not involved in the study. “It’s really cool to know what we’ve always wondered, but no one had been able to show.”
Still, studying cetaceans is complicated by their protected status and limited access to samples, which typically come from animals that have been stranded, the researchers say. For this reason, one limitation of the new study is that the researchers had to input data from different species to make their model.
“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’s like a quilt,” says Andreas Fahlman, a marine scientist at the Fundación Oceanogràfic in Valencia, Spain, who was not involved in the study. study.
As a result, the model may be missing important aspects that might be specific to other species, which have unique anatomies and even move differently, with some staying closer to the surface and others diving deeper. Taking a closer look at the circulatory system of whales and dolphins, perhaps using non-intrusive techniques like sensors that can measure blood flow and pressure, can help confirm that the computational model reflects real-life dynamics.