When a whale moves its tail up and down to swim, a wave of increased blood pressure moves from the tail to the head, but a network of vessels redirects the animal’s blood to protect the brain.
September 22, 2022
An intricate network of blood vessels in the brains of whales can protect them from damage caused by the powerful pulses of blood pressure generated during swimming.
Whales move by moving their tail up and down in the water, which, combined with holding their breath, sends a wave of pressure from the tail to the head. This would normally cause damage to the brain, but the whales manage to evade such damage.
“The compression actions create pressure pulses that can travel in the blood through veins or arteries,” he says. Robert Shadwick at the University of British Columbia in Canada. “Unlike a mammal that runs, [whales] it cannot relieve locomotion-induced pulses by exhaling air.”
Researchers first discovered networks of blood vessels known as retia mirabilia, Latin for “wonderful networks,” in deep-diving whales in the 17th century, but until now, their function was poorly understood. To investigate, Shadwick’s team created a computer model that simulates the pressure changes in a whale’s body as it swims. They based their model on the physical characteristics of 11 cetaceans, from bottlenose dolphins to baleen whales.
Their analysis revealed that retia mirabilia helps keep blood pressure in the brain constant without dampening the intensity of pulses or the power of tail wagging.
The network of blood vessels diverts pressure from the arteries entering the brain to the veins leaving the brain. This protects the cetaceans’ brains from pressure changes without changing the way blood moves in the rest of the body.
“The simulations showed that the retia [mirabilia] could eliminate more than 90 percent of the deleterious effect of locomotion-induced pulses by this transfer mechanism,” says Shadwick. “The result of the simulations was certainly surprising.”
The work also helps explain why other marine mammals, such as seals and sea lions, lack retia mirabilia. Because these animals swim through side-to-side undulations, they avoid sending a dangerous pressure pulse to the brain, reducing the need for retia mirabilia.
Magazine reference: Sciences, DOI: 10.1126/science.abn3315
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