When a whale pumps its tail up and down to swim, a wave of increased blood pressure travels from the tail to the head – but a network of vessels redirects the animal’s blood to protect the brain
September 22, 2022
A complex network of blood vessels in whales’ brains can protect them from damage caused by powerful blood pressure pulses generated during swimming.
Whales move by moving its tail up and down in the water, which, combined with apnea, sends a pressure wave from the tail to the head. This would usually cause brain damage, but the whales manage to avoid such damage.
“The squeezing actions create pressure pulses that can travel in the blood through veins or arteries,” explains Robert Shadwick at the University of British Columbia in Canada. “Unlike a common mammal, [whales] cannot attenuate locomotion-induced impulses by exhaling air.
Researchers first discovered the networks of blood vessels known as the retia mirabilia – Latin for “wonderful nets” – in deep-diving whales in the 1600s, but until now their function was poorly understood. . To investigate, Shadwick’s team created a computer model that simulates pressure changes in a whale’s body as it swims. They based their model on the physical characteristics of 11 cetaceans, bottlenose dolphins at baleen whales.
Their analysis revealed that retia mirabilia help maintain constant blood pressure in the brain without dampening the intensity of impulses or the power of tail movement.
The network of blood vessels redirects the surge of pressure from the arteries entering the brain to the veins leaving the brain. This protects the cetacean brain from pressure variations without affecting blood circulation in the rest of the body.
“The simulations showed that the retia [mirabilia] could eliminate more than 90% of the harmful effects of locomotion-induced impulses through this transfer mechanism,” says Shadwick. “The result of the simulations was certainly surprising.”
The work also helps to explain why other marine mammals such as sealed and sea lions lack retia mirabilia. Because these animals swim via lateral undulations, they avoid sending a dangerous pressure pulse to the brain, thereby reducing the need for retia mirabilia.
Journal reference: Science, DOI: 10.1126/science.abn3315
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