Fish and decompression.

[H2Andy]

decompression is an issue because under pressure, you absorb more nitrogen into your system than you would at the surface, right?

that happens because air is a compressible fluid. under pressure, the same volume of air occupies a much smaller space. or to put it another way, the same inhalation of air takes in a lot more air molecules, since they are compressed

now, since water is a non-compressible fluid, were you to breathe water through your gills, you would get the same amount of nitrogen at the surface than you would at 10,000 feet

thus, no nitrogen UNDER PRESSURE has been absorbed by your system. or rather, it's been absorbed under the same pressure as the surface, and no decompresion is needed

 

[LowVizWiz]

Finally plain engilsh <g>

 

[jeckyll]

Well, since it is here, why don't we all take a few minutes to answer this question and maybe learn something else in the process.


The first four paragraphs hit your fish question, reading the rest is well, up to you.
http://www.bishopmuseum.org/research/treks/palautz97/deepstops.html

Enjoy!

I'm glad you posed the link to the Pyle Deep Stops As I was reading through this thread I was looking for my bookmark for the same article. I just find the history of how some theories and techniques come about fascinating.

 

[Dr Deco]

Hello readers:

Partial Pressure

It is necessary to remember that “partial pressure” refers to the pressure required to dissolve a certain number of molecules of gas in water (or some other liquid). There is not any pressure exerted by the nitrogen molecules once they are dissolved. They are held in solution by the water molecules.

In order to exert a pressure, it is necessary that a free gas phase form. The pressure in the now-formed bubble will then be equal to the partial pressure of the nitrogen in solution [plus additional pressure from surface tension].

Dr Deco :doctor:

 

[coldsmoke]

I saw a program the other night about sperm whales. It mentioned a sperm whale getting bent for ascending too fast. I knew that fish cannot get bent and I didn't think that whales/dolphins etc. could get bent either, but...?

I really know very little about whale physiology but I thought that gas was stored in muscles rather than in lungs. I suppose it would make sense for a whale to get bent if gas was stored in lungs and then transfered to the blood system at depth - I guess it's not so different from a diver. But if the gas is transfered to and stored in the muscles prior to diving and no gas exchange happens at great depth, I don't understand how it could get bent. It doesn't seem like there would be any gas loading. Can someone here please verify whether a whale can indeed get bent and if so provide an explaination as to why/how?

Thanks.

 

[H2Andy]

I saw a program the other night about sperm whales. It mentioned a sperm whale getting bent for ascending too fast.

i sincerely believe that is not possible

for the nitrogen to come out of solution too fast, it must be absorbed into solution at a pressure greater than the current pressure

since the whale inhales at the surface (let's call it pressure 0) and then descends to depth (let's call it pressure +1), the air is NOT absorbed into solution at a pressure greater than whatever the current pressure is

(man, i'm trying to say that simply)

 

[Charlie99]

i sincerely believe that is not possible

for the nitrogen to come out of solution too fast, it must be absorbed into solution at a pressure greater than the current pressure

since the whale inhales at the surface (let's call it pressure 0) and then descends to depth (let's call it pressure +1), the air is NOT absorbed into solution at a pressure greater than whatever the current pressure is

Per that logic, human freedivers couldn't get DCS. But they do. It's not common, but DCS has been seen in pearl divers that make repeated deep freedives with short periods on the surface.

The air gets compressed in the lungs as the whale dives. That higher ppN2 can then go into the bloodstream or other tissues. The lung volume limits how much N2 there is to absorb, which is probably why it is a rare event for whales, dophins, etc. to get DCS.

 

[H2Andy]

The air gets compressed in the lungs as the whale dives. That higher ppN2 can then go into the bloodstream or other tissues.

ah!!

excellent explanation

 

[Digger54]

It's more like an over expansion...they hold their breath.

You'll never find a fish with MOF!

 

[havnmonkey]

I saw a program the other night about sperm whales. It mentioned a sperm whale getting bent for ascending too fast. I knew that fish cannot get bent and I didn't think that whales/dolphins etc. could get bent either, but...?

I really know very little about whale physiology but I thought that gas was stored in muscles rather than in lungs. I suppose it would make sense for a whale to get bent if gas was stored in lungs and then transfered to the blood system at depth - I guess it's not so different from a diver. But if the gas is transfered to and stored in the muscles prior to diving and no gas exchange happens at great depth, I don't understand how it could get bent. It doesn't seem like there would be any gas loading. Can someone here please verify whether a whale can indeed get bent and if so provide an explaination as to why/how?

Thanks.

Recent research has found scar tissue in the joints of many diving Mammals, Sperm whales especially. The scar tissue tends to resemble what is found in many, older Saturation divers. The feeling is that maybe they don't always have a proper surface interval and are spooked to dive back down to soon.

And yes some freedivers are now reporting symptoms of DCS... We're not built for this kind of stuff so who knows what all goes on in our bodies at extreme depth.