New research has shed light on why whales don’t suffer brain damage when they swim.
The scientists suggest that special blood vessels in the brains of animals may protect them from pulses, caused by swimming, in their blood that would damage the brain.
The researchers believe that computer modeling finally solves the mystery of the purpose of the networks of blood vessels that cradle a whale’s brain and spine, known as the retia mirabilia, or wonderful network.
Lead author Dr Robert Shadwick, professor emeritus in the zoology department at the University of British Columbia (UBC), said: “As interesting as they are, (the whales) are essentially inaccessible.
So if cetaceans can’t use their respiratory system to moderate pressure pulses, they must have found another way to deal with the problem.
Dr. Margo Lillie, University of British Columbia
“They are the largest animals on the planet, possibly ever, and understanding how they manage to survive and live and do what they do is a fascinating piece of basic biology.”
Land mammals, such as horses, experience blood pulses when galloping, where blood pressure within the body rises and falls with each step.
In a new study, lead author Dr. Margo Lillie and her team suggest, for the first time, that the same phenomenon occurs in marine mammals that swim with dorsoventral (up and down) motions—in other words, the whales.
And they may have discovered why whales avoid long-term brain damage from this.
The average blood pressure in mammals is higher in the arteries, or blood leaving the heart, than in the veins.
This pressure difference drives blood flow in the body, including through the brain.
However, movement can move blood forcefully, causing spikes in pressure or pulses in the brain.
The difference in pressure between the blood entering and leaving the brain by these pulses can cause damage.
According to Dr. Lillie of UBC, long-term damage of this kind can lead to dementia in humans.
But while horses deal with pulsations by inhaling and exhaling, whales hold their breath as they dive and swim.
Dr Lillie said: “So if cetaceans (aquatic mammals that include whales, dolphins and porpoises) can’t use their respiratory system to moderate pressure pulses, they must have found another way to deal with the problem.”
The researchers theorized that the blood vessels use a pulse transfer mechanism to ensure that there is no difference in blood pressure in the animal’s brain during movement, other than the average difference.
Essentially, instead of dampening the pulses that occur in the blood, the vessels transfer the pulse from the arterial blood entering the brain to the venous blood leaving, maintaining the same pulse strength, thus avoiding any pressure difference across the brain. the brain itself. .
The researchers collected data on 11 cetacean species and put the numbers into a computer model.
“Our hypothesis that swimming generates internal pressure pulses is new, and our model supports our prediction that locomotion-generated pressure pulses can be synchronized by a pulse-transfer mechanism that reduces the resultant flow pulsatility by up to 97 percent. %,” Dr. Shadwick said. .
He suggested that the model could potentially be used to ask questions about other animals and what happens to their blood pressure pulses when they move, including humans.
The researchers say the hypothesis still needs to be tested directly by measuring blood pressure and flow in the whales’ brains, something that is currently not ethically and technically possible, as it would involve placing a probe in a live whale.
The findings are published in the journal Science.