Science Questions

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

Tue, 22nd Mar 2016

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Guido asked:

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




We put Guido's question to zoologist Chris Basu... Southern right whale by Brian Skerry

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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I belive it is because they are not breathing compressed air.

Mazurka, Thu, 13th Jan 2011

I must admit that I had to look up at least part of the answer to this one.  So much for my chances at beating Watson at Jeopardy.

No, whales don't get the bends...  at least not now...  but there are some reports of whale fossils indicating bends symptoms in their ancestors. 

Part of the answer has to do with the difference between Scuba diving and snorkelling and "Free Diving".

The bends is essentially gas bubbles forming in your blood vessels as the pressure decreases from high pressure ad depth to low pressure at the surface.

Let's first consider humans.  It is difficult to get the bends from snorkelling and free diving because one takes a deep breath, goes down, then comes back up to atmospheric pressure and breaths in and out.

When scuba diving, you go down and breath mixed air for a period of time.  The scuba, or supplied air apparatus has to equilibrate the pressure to the surrounding water pressure (1ATM for every 33 feet).  This will tend to force more gas into your blood.  Oxygen in the blood is good and gets consumed by the tissues.  CO2 tends to dissolve into carbonic acid.  While it makes your soda fizzy, it isn't particularly dangerous in your blood except for the acid balance which doesn't seem to be an issue.

Nitrogen, however, doesn't dissolve a lot in the blood.  Too much nitrogen dissolved in the blood is bad, so, when it is pressurized, more dissolves in the blood and one risks Nitrogen Narcosis.  To counteract the tendency to get Nitrogen Narcosis, deep divers will use a Helium or Neon oxygen mixture, two other gasses that don't easily dissolve in the blood, but can be forced in under pressure.

As you ascend, you need to get the dissolved Nitrogen, Neon, or Helium out of the blood which is dependent on several factors including the pressure and time under water.  And, it is not quick to equilibrate.

So, what about the Free Diver?

They take a big gulp of air...  and dive as deep as possible...  then come back up for their next breath.  It isn't a problem with a single dive, as one can't stay underwater very long.

With multiple dives, it becomes a problem as repeated dives can force more nitrogen into the blood until it eventually gets to the point where it will start bubbling and one gets the bends.

So...  can a whale only occasionally do a deep dive...  for a brief time?  NO.

The Whales have essentially developed 2 mechanisms to protect themselves.

First...  they apparently have an oil in the lungs that absorbs Nitrogen, and prevents it from entering the blood stream.

Second.  While the human takes in a big gulp of air before the dive, whales don't.  They have more hemoglobin in their blood than humans.  So...  on the surface, they oxygenate the hemoglobin.  Then they exhale before making their dive.  So the lungs are not full of pressurized nitrogen while they are swimming underwater, and thus, the nitrogen is not forced into the bloodstream.

They, of course, have to have some air to clear the blowhole, but not a lot. CliffordK, Fri, 14th Jan 2011

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