Researching Earth’s largest animal is not for the faint of heart. Whales, and in particular their biological systems, have been essentially inaccessible for scientists to study thus far, due not only to their size, but their habitat as well. These roadblocks, however, have not stopped researchers from finding innovative and ethical ways to learn more about these creatures. One such group at the University of British Columbia has recently used computer models to model how a whale’s circulatory system works while swimming.
To understand how such large mammals are able to swim without breathing for a prolonged period of time, we first need to look at blood flow. Mammals experience changes in their blood pressure that enables their blood to be pumped throughout their body. A difference in pressure on one side causes blood to move to the other, and vice versa. Blood pressure is often higher for oxygenated blood that is exiting the heart, or the arteries than it is for blood that is about to enter the heart or veins. This process of blood flow usually works perfectly, until it is interrupted by an animal exerting itself. Sudden movement or exertion, simply referred to by the authors of the papers as ‘locomotion,’ can cause spikes in blood pressure. These spikes, termed ‘pulses,’ can cause brain damage as blood moves through the brain, as they can cause a difference between the pressure of blood entering the brain to the blood leaving. These damages are often long-term and can include dementia.
Mammals have found different ways of dealing with these pulses. For example, horses can negate the effects of brain damage by breathing in and out, taking one breath per stride to synchronize their movement with their blood pulses. This is known as the Windkessel effect, and it requires the animals to actually dampen the pulses in the blood. Whales, however, do not have this luxury, as they hold their breath while swimming. So this is the mystery that has evaded scientists for so long: how do whales avoid this brain damage when they swim?
The answer lies in a whale’s “retia mirabilia” or its “wonderful net,” a term that refers to the network of blood vessels that surrounds a whale’s brain. Previously, the use of this structure was unknown, but researchers theorized that it had to do with the question of avoiding brain damage.
To test this theory, they collected circulation and swimming data from 11 different species of whales, porpoises, and dolphins, all of which are mammals that have retia mirabilia. Then, they modeled different explanations for how whales are able to decrease the blood pulses and tested each hypothesis for its likelihood of being true.
What they found was that it is most likely that whales use a “pulse transfer” mechanism in order to avoid brain damage from the difference in pressure. This means that instead of simply dampening the pulses, the retia transfers the pulse that is entering the brain to the blood that is exiting. This keeps the same strength of the pulse that is entering and exiting the brain, therefore avoiding any pressure or damage to it.
The researchers note that their model and process could potentially be used to research other animals, to potentially explain how they deal with this circulatory problem. The university also points out that the next step to confirming this would be to get real-world circulation data from a whale to test this against, which for practical and ethical purposes, is completely impossible. That being said, the team still plans on using their computer model to research their theory further, citing how invaluable simulations are when researching such biologically complex creatures.
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