[thedoc]

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


Asked by Guido


                                        Visit the webpage for the podcast in which this question is answered.

[chapter podcast=1001320 track=16.03.22/Naked_Scientists_Show_16.03.22_1004904.mp3]  ...or Listen to the Answer[/chapter] or [download as MP3]

[Mazurka]

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

[CliffordK]

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.