Study sheds light on why whales do not get brain damage when they swim

Scientists suggest special blood vessels in the animals' brains may protect them from pulses in their blood that would damage the brain.

New research has shed light on why whales do not get brain damage when they swim.

Scientists suggest that special blood vessels in the animals’ brains may protect them from pulses, caused by swimming, in their blood that would damage the brain.

Researchers believe computer modelling finally solves the mystery of the purpose of the networks of blood vessels that cradle a whale’s brain and spine, known as retia mirabilia, or wonderful net.

Senior author, Dr Robert Shadwick, professor emeritus in the department of zoology at the University of British Columbia (UBC), said: “As interesting as they are, they (whales) are essentially inaccessible.

“They are the biggest 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 pulses in their blood when galloping, where blood pressures inside the body go up and down on every stride.

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 dorso-ventral (up and down) movements – in other words, whales.

And, they may have found out just why whales avoid long-term damage to the brain for this.

Average blood pressure in mammals is higher in arteries, or the blood exiting the heart, than in veins.

This difference in pressure drives the blood flow in the body, including through the brain.

However, movement can forcefully move blood, causing spikes in pressure, or pulses to the brain.

The difference in pressure between the blood entering and exiting the brain for these pulses can cause damage.

According to Dr Lillie, of UBC, long-term damage of this kind can lead to dementia in human beings.

But while horses deal with the pulses by breathing in and out, whales hold their breath when diving and swimming.

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 theorised that the blood vessels use a pulse-transfer mechanism to ensure there is no difference in blood pressure in the animal’s brain during movement, on top of the average difference.

Essentially, rather than dampening the pulses that occur in the blood, the vessels transfer the pulse in the arterial blood entering the brain to the venous blood exiting, keeping the same strength of pulse, and so, avoiding any difference in pressure in the brain itself.

The researchers collected data on 11 cetacean species and put the figures 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 synchronised by a pulse transfer mechanism that reduces the pulsatility of resulting flow by up to 97%,” Dr Shadwick said.

He suggested that the model could potentially be used to ask questions about other animals and what is happening with their blood pressure pulses when they move, including humans.

The researchers say the hypothesis still needs to be tested directly by measuring blood pressures and flow in the brain of whales, something that is currently not ethically and technically possible, as it would involve putting a probe into a live whale.

The findings are published in the Science journal.