Whales and Dolphins get the bends?

[Dr Deco]

Hi gertjan:

Stabilized Nuclei

For all practical purposes, bubbles formation is actually growth from nuclei. The origin of the nuclei is debatable. Certainly thermal movement and fluctuations in the position of molecules will play a role. As the temperature increases, the void increase in size. The classical nucleation theories of the 1920s and onwards does not explain the tensile strength of liquids however. Tensile strength depends on the creation of a avoid in the liquid, and tensile strengths are always lower than predicted. The presence of nuclei induced into the liquid is suspected. Surfactant compounds might stabilize these “motes”, but organic liquids also are known to have nuclei and surfactant stabilization is not suspected to occur in organic liquids.

Vaporous and Gaseous Cavitation

What is inside the nuclei or microbubbles depends on the gases dissolved in the liquid. If there are no dissolved gases, then only the vapor of the liquid is present and we have “vaporous cavitation. “ This is what occurs during the boiling of a liquid.

If dissolved nitrogen and oxygen, for example, are present (from air), then we have gas and vapor both stabilizing the bubble. Because of surface tension, the bubbles will always shrink. If the gas is dissolved in abundance (e.g., under pressure), then “gaseous cavitation can occur when the hydrostatic pressure is reduced. This is referred to as “effervescence” and is what occurs in carbonated beverages and divers (DCS).

Dr Deco :doctor:

 

[Gertjan]

Hi,

OK, got it. I guess cavitation is a more generic term.

Now carbonated softdrinks are a resonable model system to visualize bubble formation etc. Actually, I did a fun experiment the other day where I put a bottle of coke briefly into an ultrasonic bath (we have those in the lab for cleaning purposes). Wow, quite spectacular, the coke almost got on the ceiling!, no kidding

I know, it doesn't make for a good model system if you want to know what happens in vivo quantitatively but it sure shows the effect of a strong ultra sonic sound waves nicely. Also, it's pretty obvious that in this case there are gas nuclei present in the liquid.

Now, getting back to the original question: Does sonar really have anything to do with the observations made in beaked whales or not?

I guess, the first thing that needs to be established is whether the whales actually died from the bubble damage observed in the liver and other organs. Subsequently, if so, one needs to investigate any corrrelation with the sonar and the formation of these bubbles and find a good model for the bubble formation mechanism in this case which can be tested experimentally. (Since the mechanism might be totally different from 'regular DCS', it might not be surprizing that different organs are involved)

Now, I can understand the critizism because the questions above have not been answered at all (in Nature). However, to me the experimental results are strinking worth sharing with a broad audience. It should stimulate research and possibly provide a clue to the strange whales beachings linked to sonar testing. Isn't that one of the missions of a magazine like Nature? Finally, it happens very often that experimentalist speculate on the origin of their findings, it's their job to report the experiments correctly but the interpretation is free for anyone.

In short, I agree with most of the comments on the (speculated) origin of the observed phenomena but nobody has convinced me of the fact that the actual observations are wrong. Hey, it's not even my paper, I'm trough with defending other peoples work!

I will follow any related research closely, who knows, may they were wrong or ...

Cheers!

 

[Dr Deco]

Hi Gertjan:

Live and Let Live

I am a big defender of allowing folks to write and publish. In the case of the Nature paper, however, I believe that it was inserted to promote essentially [might we say] a “political cause.” Especially since the next day it was on National Public Radio. It was clear [to me] from the paper that it was not sent to someone sufficiently knowledgeable in barophysiology to allow the shortcomings to be addressed.

Now, I do not know if marine mammals do or do not acquire DCS in the presence of sonar. I actually do not know if they get DCS at all. DCS might be dangerous for their health, and thus they evolved in a manner that protected them. Possibly there is a lack of nuclei in their tissues. Were this to be true, then ultrasound irradiation should not make a large difference.

The bubbles described in the article in Nature are not found in barophysiology literature. Actually, few papers have been written about DCS bubbles, as they are very ephemeral and “evaporate” quickly. The writers did not describe bubbles in any location but the liver. The paper does not state (unfortunately) just what organs were actually examined, although it states that "several organs were examined." Absent is how long after beaching was the necropsy.

If someone were to hand me a report saying that such and such was found on the beach, and the only pathology found was bubbles in the liver, I would not say “Clear sign that it died of decompression sickness.” Cavitary bubbles in the liver is not a clear indication of DCS.

It was certainly an interesting paper, however. And it was interesting to hear of the can in the ultrasound bath. I have never tried, that since I do not have an U/S cleaner.

Dr Deco :doctor: