Snorkelling elephants

[Zept]

I am putting this in Dive Medicine b/c it's a physiology question, but feel free to kick it into some other forum if you don't want to answer questions about elephants!

The BBC Web site has a story about snokelling elephants. American scientist Dr John West says elephants have special tissues in their lungs that enable them to get into the water, stick their trunks up over their heads and breathe against the pressure gradient. British zookeeper Nick Ellerton says he doesn't see why they'd need special lung tissues.

Opinions? From what I've read about humans snorkelling, seems to me that elephants must be doing something different if they can suck air down their trunks when their lungs are 1-2m (at a guess) below the surface. Then again, I'm not a physiologist or even a physicist.

What do you think?

Zept

 

[The Iceni]

Zept once bubbled...
Dr John West says elephants have special tissues in their lungs that enable them to get into the water, stick their trunks up over their heads and breathe against the pressure gradient. British zookeeper Nick Ellerton says he doesn't see why they'd need special lung tissues.
. . .

Zept

All the elephant needs is strong enough intercostal muscles, ribs and diaphragm in order to expand the chest/lungs against ambient pressure at say 1 metre (1.1 bar). Being the size they are and their love of water holes, it would not surprise me to learn that these muscles could easily do the job. However, I am no vet. Perhaps they have some other organ we do not but they are mammals so I doubt it.

I also doubt specialised lung tissue is required.

I wonder how they would cope with a regulator and what their SAC is? An 80 cf tank certainly wouldn't last long!

 

[scubadoc]

Apparently, due to their aquatic ancestry - elephants don't have a pleural space as do other mammals. This is said to facilitate their ability to suck up water in their trunks with their mouths open and to snorkel.

See this web site for an in depth discussion: http://www.eurekalert.org/pub_releases/2002-08/aps-fei082602.php

 

[The Iceni]

While I can appreciate the problems the parietal pleura would face - it is the same as the problems experience by the lining of the sinuses when a diver suffering from sinus congestion dives;- The blood supply to the membranous lining in the sinus is disrupted by the excessive blood pressure relative to the pressure within the sinus itself. Perhaps, indeed, this does not occur in elephants because as the link describes, the blood supply to the parietal pleura is less.

However, what amazes me is that no reference is made to the pulmonary circulation when an elephant is snorkelling as described. If the elephant's heart is situated at 2 metres the venous return to it's heart must be referred to ambient pressure at that depth so the pulmonary arterial pressure will be a much greater problem that any problem with the pleural blood supply and the physics of respiration. Reference to the changes to the circulation in free divers confirms this.

This is an interesting problem they appear to have solved. Perhaps the anatomy of their hearts is different to that of humans?ut:

 

[Zept]

Thanks for the link, Scubadoc. No idea what I'm going to do this with this information... I don't do much snorkelling with elephants... but it's interesting all the same.

Dr T, since blood is a liquid, presumably the elephant's heart has to pump against a significant pressure difference even when it is on land? Or am I missing something?

Zept

 

[The Iceni]

Zept once bubbled...
Dr T, since blood is a liquid, presumably the elephant's heart has to pump against a significant pressure difference even when it is on land? Or am I missing something?

Zept

This can get complicated, but for this discussion just consider the heart as a pump which increases the pressure of the blood relative to the veins by an amount required to cause it to circulate around the body. If this extra pressure needs to be 0.25 bar, on the surface the absolute blood pressure would be 1.25 bar. (If you think about it an empty scuba cylinder, which has a guage pressure of zero contains air at 1 bar;- The absolute pressure within an empty tank is 1 bar.)

At 10 metres scuba, the "guage" blood pressure will still be 0.25 bar as it is relative to ambient pressure but the absolute pressure within the arteries will be 2.25 bar and at 20 metres it will be 3.25 bar, but no matter what depth the blood pressure is recorded by a sphygmomanometer (or indeed measured by the body) it will still register 0.25 bar.

Now, back to snorkelling elephants and free-diving humans.

In summary, a snorkel cannot raise the pressure within the chest to that of ambient pressure, as a scuba regulator can.

At 2 metres the ambient pressure will be 1.2 bar and if the muscles of the chest wall and diaphragm are strong enough to keep the lungs inflated in a snorkeller against this pressure, the pressure within the chest cavity will remain at the surface pressure of 1 bar.

The result is a relative increase of pressure of 0.2 bar in the venous return to the heart, as it lies within the chest cavity, while the great veins do not.

In free divers this causes blood to follow the pressure gradient and to pool in the pulmonary circulation (until this is once more opposed by the increased pressure within the chest).

The maths is as follows (Boyle's Law).

If the lung volume is 10 litres on the surface;

P1 V1 = P2 V2

1 bar x 10 litres = 1.2 bar x "X" litres

X = 8.333 litres, a difference of 1.7 litres which is the volume of blood needed to enter the chest to compress the air cells and raise intrathoracic pressure to an ambient 1.2 bar at a depth of 2 metres.

If, as in humans, the muscle of inspiration are not strong enough to oppose a snorkelling pressure gradient of 0.2 bar, the lungs are simply deflated through the snorkel by this pressure. When you snorkel dive you lose this low pressure connection to the surface but the air is compressed nevertheless.

Well! I hope that clears that up.

 

[Laurence Stein DDS]

PEANUTS!

Just feeling silly

Larry Stein

 

[Laurence Stein DDS]

We all know how long a giraffe's neck is. Did you know that when the animal bends its head down, the blood column undergoes a tremendous pressure change? We are not talking about mm of water but meters of water change in pressure.

Giraffe's don't suffer from strokes. Another animal mystery.

Trivia from dental school/physiology. I also noticed that my professors never suffered from strokes no matter how hard a time we gave them.

Regards,

Larry Stein

 

[The Iceni]

Laurence Stein DDS once bubbled...
We all know how long a giraffe's neck is.

Does this mean they can wade across a five meter deep river?

 

[Laurence Stein DDS]

Paul,

Only if they wear a properly adjusted wadebelt.

Larry Stein