Whales and Dolphins get the bends?

[Rickg]

BIGSAGE136 once bubbled...
http://www.newscientist.com/news/news.jsp?id=ns99994254

If this isnt credible its as close to the scientific knowledge on this
subject matter we'll get without some heavy research.

I don't know if I would go so far as to call this "scientific knowledge". If you go to the very bottom of the article that is linked by the URL in BIGSAGE136's email you will find that the source for this news article is a actually a "Brief Communications" in a publication named "Nature".

I don't believe there is any requirement for articles/letters published in the "Brief Communications" section of "Nature" to be peer reviewed by fellow scientists prior to publication. This allows for some scientific leeway for speculation that would not be permitted in an actual article because there is no peer review process.

Here is the URL to the article in "Nature" but unfortunately you can't view the entire article unless you subscribe to "Nature" or wish to purchase an individual article.

http://www.nature.com/nature/links/031009/031009-3.html

What is really interesting though is what appears to be the timing invovled. It appears that someone tips off numerous other news publications that such an article/letter to the editor is going to be published in hopes that the "message" will get picked up by other news publications and get increased publicity. The 3 news articles below all ran shortly after the October 2003 issue of Nature hit the street.

San Diego Union Tribune
http://www.signonsandiego.com/news/uniontrib/thu/news/news_1n9whales.html

Washington Post
http://www.washingtonpost.com/wp-dyn/articles/A63215-2003Oct8.html

CNN
http://www.cnn.com/2003/TECH/science/10/08/whale.sonar/index.html

I think someone is going to do a lot more research before a definitive answer about this issue can be reached.

Rickg

 

[Gertjan]

May I comment that brief communications in Nature magazine are peer reviewed.

 

[Dr Deco]

Dear Scuba Board Readers:

Call Tripe Where Tripe Is Served ut:

If that paper was reviewed, someone should have a very red face. That was a poor piece of science, a poor job of reporting, and a poor review.

This is a very “hot button” issue in marine science, and it deserved a better piece of work. Shame on a fine journal such as Nature.

Dr Deco :doctor:

 

[Gertjan]

Dear Dr. Deco,

If you've read the article in Nature you must have noticed that the scale of the bubbles was on the order of centimeters! Even I would not need doppler to detect such size bubbles, the authors comment that the liver had the most striking bubble damage, hence their choice. They also mentioned other organs being affected.

Finally, I do not have any problems with the fact that such striking results are shared quickly with a broad audience, even if a clear explanation is not available yet. Call it news. Maybe this offers scientists a clue as of where to look. I agree that much more research needs to be do to come to a satifactory explanation.

Friendly,

Gertjan Koster

 

[Dr Deco]

Hello Gertjan:

Problems

I found many problems with the Nature article:

The is no mention of when the animals were necropsied. That determines decompression bubble persistence.

There is no mention that bubbles were present or not in fat or muscle tissue. The locations are easy to study and are the real, experimentally defined, loci of decompression bubbles.

The bubbles in the liver are strange. Diving literature does not mention this organ as having decompression bubbles. This goes back to Gersch and Catchpole the 1950s.

The liver gas phase was enormous in volume. We are looking a gas bubbles of millimeters across; this is unusual for decompression bubbles.

The bubbles reported in the literature were said to be stabilized (or something to that effect). It appears that some process requiring time modified them. This is not typical of decompression bubbles.

Decompression sickness, per se, results from a gas phase in the connective tissue (pain) or neurological tissues. Generalized bubbles following a dive are not decompression sickness. Many divers have silent bubbles in the blood vessels following a dive. They are asymptomatic bubbles.

While a marine mammal might develop bubbles on an ascent, even a fast ascent, that is not necessarily decompression sickness.

The connection between ultrasound and bubble formation in living tissue is not strong.

DCS

I am not arguing that this mammals do not have DCS problems. I am supply saying that this paper does not really support the thesis. The fact that the paper was reviewed on National Public Radio the next day indicates to me that it was on mammals and not DCS – and motivated by more than pure science.

Dr Deco :doctor:

 

[segal3]

Dr Deco once bubbled...
Dear Scuba Board Readers:

”Does he know Cornwall, who only Cornwall knows?”

King Lear? Or no...?

~Matt Segal

 

[Jai Bar]

When Sonar (low frequency ultrasound) waves pass through a liquid with dissolved gas, the pressure caused by these waves changes from positive to negative typically in a frequency of 250KHz (e.g. 250000 compression/decompression cycles each second) . If the peak pressure is above a certain threshold, it can cause several types of cavitation effects which can cause not only bubbles but also physical damage to tissues. The pressure-threshold for cavitation depends on the frequency of the device (e.g. Ultrasound, Sonar etc.), its pressure field distribution, and liquid condtions (temperature, amount of dissolved gas, viscocity, fluid velocity etc). Tissues are semi-liquid for this purpose. For example, Ultrasound imaging devices can induce cavitation in human body, and usually their power output is attenuated in order to make them safe- however, cavitation has been observed when using contrast enhancers based on micro air-bubbles. IMHO, in some circumstances, doppler ultrasound can cause cavitation effects on divers with saturated tissues (after dives).

Getting far away from the Sonar source, one can assume it is a point source, and peak pressures will decrease inversely-proportional to the distance. I don't know how much power these things generate, but I assume it's fairly high- I wouldn't like to be diving near one of these devices :wacko:

 

[Dr Deco]

Hi Jai Bar:

Cavitation

It is doubtful that the intensity of the ultrasound is sufficient to provoke de novo cavity formation. It was the initial studies of EN Harvey (yes, the same Harvey that introduce micronuclei to the diving world) that indicted the ultrasound merely enlarged the existing nuclei.

If micronuclei are not present, the ultrasound will have no effect. The concentration (size-number distribution) of nuclei in the tissue of marine mammals is not known. Likewise, it is not known in humans but some things can be inferred from their decompression characteristics. We do to have much knowledge about marine mammals with respect to decompression. They appear to be resistant, but the reason is not known.

Dr Deco :doctor:

 

[Gertjan]

Hi--Does anyone know what the angular distribution is of this type of sonar (what frequency range are we talking about actually? the papers I've stumbled upon were only referring to 'low' to 'mid' frequency)? I.e., is it a sort of beam which is scanned or a point source? Someone here in our department mentioned that it might be a strongly collimated/focussed beam.

Another question: Does cavitation include bubble formation from dissolved gasses or only the solvent (pressure drop below the vapor pressure)? My guess is those are two different things.


Cheers!

 

[Dr Deco]

Dear segal3:

Cornwall?

The fellow in King Lear was the Duke of Cornwall. The short quote of mine refers to those who know much about their field (in this case marine mammals and only marine mammals) but write papers in decompression (pathology of DCS) that is outside their field, and then they make the broad pronouncements.

:book2: Dr D is a big fan of history and especially the history of technology. The quote (I believe) appears in The Lunar Men, a book concerning the name adopted by a society of [amateur] scientists in the English Midlands of 1770. While not at all about diving (it mostly deals with the pottery works of Wedgwood), in it we meet many of those individuals initially associated with several of the concepts and equipment of physiology. Among these are Joseph Priestly, James Watt, Thomas Beddoes, and Humphrey Davy.

Dr Deco :doctor: