Why is it whales do not get the "bends"?

22 March 2016


Encounter with a Southern right whale, by Brian Skerry (c)



Why is it whales do not get the "bends"?


We put Guido's question to zoologist Chris Basu... Ben - Well, spoiler for the question - they actually can get the bends, we think. The bends is decompression sickness so, as you say, when scuba divers go down underwater they're using equipment which matches the pressure of the air to the pressure of the water around them. So, as you go down underwater, the water exerts massive pressure, it's pushing down on you. When you're breathing in air under pressure, air is about 78% nitrogen, under pressure that means more of the nitrogen gets pushed into your blood and when divers want to come back to the surface, they come up to the surface, the pressure around them decreases and all that excess nitrogen gas comes out of their blood. So imagine if you've got a....

Chris - So when you say comes out of their blood you mean as in while it's still in the blood?

Ben - Exactly, if you imagine like a can or a bottle of fizzy drink, if you open the cap really quickly, if you open it too quickly you see all these bubbles suddenly magically appearing, whereas if you do that slowly, you don't see that happening as much and that's exactly the same as what's happening in the blood of scuba divers when they're coming up. Now.

Chris - So when they come up slowly, why doesn't it happen?

Ben - Exactly. When they come up slowly, it allows the blood to form an equilibrium with the air much more slowly.

Chris - In the lungs?

Ben - Exactly. If you do it too quickly, then all that gas comes out the blood as bubbles and that causes problems.

Chris - So what you're saying is then, if they got lots of this dissolved nitrogen in their blood as a scuba diver, as they surface slowly because the blood's going past their lungs, it can slowly surrender the nitrogen to the lungs, the lungs inflate, they breath out the nitrogen harmlessly?

Ben - Exactly. So, in effect, the divers are actually off gassing. They're breathing out that nitrogen gas slowly and safely.

Chris - So what do the whales do then?

Ben - The whales have one major, major advantage - they're not breathing compressed air. When whales come to the surface, they take a breath. A lot of whales actually take a breath and they exhale before they go down. So they've got environmental sea air, if you like, and as they go down that air actually gets compressed but it's not the same as a scuba diver breathing in massive lungs full of.

Chris - Compressed air?

Ben - Pressurised air, exactly. But they still have a little bit of air in their lungs. They can't empty their lungs and their trachea, their windpipe completely so they've got this little bit of air. It means they can actually get some pressurised nitrogen seeping into their blood but it's in really, really, small amounts and they've got a couple of things that helps them. They've got lots of special fat in their body and that helps to actually mop up the excess nitrogen and they can also store the air in funny places. Their trachea (windpipe) is actually distensible so when they go down their lungs get compressed but a lot of that air gets forced up into their trachea and it doesn't enter the blood at all. It's really amazing these beach whales, they can actually dive down to three kilometers, which is 300 times the atmospheric pressure of the air.

Chris - Incredible, isn't it? So you mentioned at the beginning you said well they actually can get this so why do they occasionally get the bends then?

Ben - The other thing that they do, they're very sensible. Like scuba divers they also don't come straight up to the surface, they come nice and slowly but when something disturbs that behaviour, they might actually be prone to getting the bends. A few years ago, people were noting certain associations between sonar activity of military vessels and whale strandings and they actually found in these stranded whales the telltale signs that they had the bends, they had decompression sickness. When people look at bones of whales, bones actually have little telltale signs as well when the animal's had chronic exposure to decompression sickness, they have these little spots on the bone. So we can actually see that whales do from time to time tend to suffer from it but it's something that they have learned to live with.


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