If you look at parts of the circulatory system of whales and dolphins, you might think you’re looking at a Jackson Pollock painting rather than blood vessels. These cetaceans have a particularly dense, complex network of blood vessels, mostly connected to the brain and spine, but scientists didn’t know why. This is evidenced by a new analysis nets protect cetacean brains from the pulses of blood pressure that animals endure while diving deep into the ocean, researchers report in September 23 Science.
Whales and dolphins “have gone through these really amazing vascular adaptations to support their brains,” says Ashley Blavas, a marine scientist at Duke University Marine Laboratory in Beaufort, North Carolina, who was not involved in the study.
A network of blood vessels called retia mirabilia, meaning “wonderful nets,” is found in some animals other than cetaceans, including giraffes and horses. But such webs are not found in other aquatic vertebrates that move differently than whales, such as seals. Therefore, scientists suspected that the cetacean Retia mirabilia plays a role in controlling spikes in blood pressure.
When whales and dolphins dive, they move their tails up and down in a wave-like manner, which causes spikes in blood pressure. Terrestrial animals, which experience similar surges as galloping horses, are able to release some of this pressure by exhaling. But some cetaceans held their breath dive for a long time (ЗН: 23.09.20). Without the ability to relieve this pressure, these blasts can rupture blood vessels and damage other organs, including the brain.
In the new study, biomechanics researcher Margot Lilly 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 mimic the animals’ retia mirabilia. It turned out that the arteries and veins in this tangle of blood vessels are very close and can even connect at times. As a result, the retia mirabilia can equalize the difference in blood pressure that occurs during diving, possibly by redistributing blood impulses from arteries to veins and vice versa. In this way, the networks eliminate, or at least attenuate, the huge spikes in blood pressure that would otherwise reach and destroy the brain.
Networks “equalize [blood flow] so that you never lose the blood that’s in the vein, and it doesn’t clot down on its own, and you don’t have the arterial blood that’s shooting up quickly going into the brain,” says marine biologist Tiffany Keenan of University of North Carolina Wilmington, who was not involved in the study. “It’s really nice to know something that we’ve always been interested in, but no one has been able to show.”
However, studying cetaceans is difficult because of their protected status and limited access to samples, which usually come from stranded animals, the researchers said. For this reason, one of the limitations of the new study is that the researchers had to input data from different species to create their model.
“They take a little bit from here and a little bit from there, mixing dolphin with beluga and beaked whale – it’s kind of like a blanket,” says Andreas Fahlman, a marine scientist at the Oceanographic Foundation in Valencia, Spain, who was not involved in the study.
As a result, the model may miss important aspects of other species that have unique anatomy and even move differently, with some staying closer to the surface while others dive deeper. Closer study of the circulatory system of whales and dolphins, perhaps using non-intrusive methods such as sensors that can measure blood flow and pressure, could help confirm that the computational model reflects real-world dynamics.
