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"The bends" is one of the biggest risks that humans have to deal with when diving, but why don't marine animals, which are diving all the time, get them?

Hosted by: Olivia Gordon

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Although hollywood would have divers worrying about mega-sharks, trained professionals know that getting the bends is one of the biggest risks they face. That funny name given to the pains, numbness, or other physical complications that divers sometime experience when they surface belies just how dangerous the illness can be.

But, there are animals that dive all the time. Like seals and and whales for example. Some of them go way deeper than humans could ever even dream of — like, over thousand meters below the surface.

So why don't marine animals get the bends? Well, it turns out they do, sometimes, but they also have adaptations that help keep them safe. The bends, or decompression sickness, happen because of the higher pressure divers experience.

When fluids — like blood — are under greater pressure, they can absorb more gas. So that pressure means more of the air in a diver's lungs — especially nitrogen gas — is absorbed into their blood, and therefore their tissues in general. When that diver surfaces and the pressure drops, their blood can no longer hold all that gas, so it starts to bubble out again — and lots of those bubbles all at once.

They can damage tissues, which might mean a little tiredness, joint pain, and tingling, or, in the worst cases, spinal cord injury or even death. While this is mostly a concern for SCUBA divers because they're breathing in more nitrogen with every breath, there have been a few cases in breath-holding free divers too, especially after repeated dives. In general, the deeper a diver goes and the longer they stay down, the more gas is absorbed.

And once that happens, returning to the surface slowly so the bubbling is minimized is basically all you can do to avoid major problems. But it's hard to come up slowly when, you know, you need to breathe. Since many marine animals dive a lot and for long periods of time, it really begs the question why they don't seem to have this problem — and if their tricks can help us dive deeper or for longer.

In most animals that dive for a living, the biggest advantage they have is that they can collapse part of their lungs and have their blood flow over the deflated part. This creates what's called a ventilation-perfusion mismatch. Basically, there's less blood where the gas is, so less gas gets absorbed.

This ability is possible because their lungs are super stretchy and they have a stiff windpipe where all the air that gets squeezed out can sit. Studies show that seals can divert up to 70 percent of their air, for example, and sea lions up to 57 percent. Whales and dolphins seem to do a similar thing, and they may go a step further.

Research suggests they have partially deflated lungs all the time — then, when they dive, they can tweak the distribution of air and divert their blood to create the mismatch. This is similar to what sea turtles seem to do — they move their blood around, rather than the air. But what's really cool is that scientists think the degree of deflation or the routing of blood flow can be somewhat controlled in some species — it doesn't just happen passively as the animal dives.

That could explain the few cases where we do see marine animals with the bends: when they're caught in nets or have been stressed out. For one reason or another, they either couldn't or didn't control their ascent. But while separating the air in your lungs from the blood is a neat trick, it also means less oxygen gets into the blood — the mechanism affects all gases in the lungs.

Marine mammals seem to deal with this by storing and transporting more oxygen in their bodies in the first place — reserves that they can tap into while they're down deep. Other species, like turtles, likely tolerate lower oxygen levels in general. While we've got a lot of this figured out in certain species, there are some mysteries that remain — like what penguins and other diving birds do.

But since the ways animals avoid the bends all seem to be built into their bodies, it's not likely that they're going to help people avoid decompression sickness. No stretchy lungs for us. Thanks for asking!

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