Yo-yo profiles

[_coni_]

Hello,

I would like to know exactly what is known about diving yo-yo profiles, as long as you never reach a decompression ceiling. As I read on this forum in posts by Dr. Powell, the usual explanation that bubbles absorb gas and grow while ascending due to tissue off-gasing to the blood, and then get compressed when descending and thus manage to travel through the pulmonary filter abd to the arterial side, does not stand.

So, just to make sure: has it been experimentally observed that yo-yo profiles generate many bubbles, or are DCS-prone? Do you know of some references?
Since the usual explanation seems to be wrong, what are the possible explanations for the risks of yo-yo profiles?

Application: with my main certification agency, we regularly practice controlled buoyancy lift of a victim. A typical training profile is 4 repetitions of: descending to 20m, then ascending at ~12m/min to 3m. Is there any DCS risk with this profile if done at the very beginning of a dive? And if done while already partially saturated? (An instructor told me that about 1/4 of all DCS cases with PADI happen while practising this exercise for the Rescue Diver class, but maybe its due to trainees ascending too fast or breaking the surface).

Thanks for any good explanation!

 

[doctormike]

I think that the story of my chamber ride is good reading for anyone concerned about the DCS risk of multiple ascents while staying within NDLs!

 

[chrisch]

Hello,

I would like to know exactly what is known about diving yo-yo profiles, ...

Not much is sadly the answer. For a long time it was believed that less than 10m (30 feet) you were OK until the advent of fish farming. DCS has been observed in some fish farm divers that repeatedly dive to just a few metres many times a day.

There is a free PDF paper from the UK HSE (like US OSHA) here - http://www.hse.gov.uk/research/rrpdf/rr214.pdf

 

[TSandM]

I read the paper linked above, and I'm quite puzzled at where some of the information comes from. They make a definitive statement that muscle has slower uptake and slower offgassing than brain or viscera. In the past, I looked quite hard for any studies generating that type of information, and I was unable to find any. All I ever got was information that the Navy had done such studies in the remote past, but the results were not published for general consumption. The graph showing how their mathematical model predicts gas loading in viscera, brain and muscle, depends on that information. Their statement that muscle doesn't generate bubbles but brain does is, I assume, entirely based on the math, as to my knowledge, nobody has a reasonable way to measure bubble formation within the brain.

 

[Dr Deco]

Hello Readers:

Yo YoProfiles

I do not have any data on yo-yo profiles, eitherin the lab or the field. I have heard that shellfish divers (goeducks) inWashington State perform these and do not encounter problems. I believe the depths are 30 to 60 fsw.

Tissue Bubbles

Brain tissue is considered “fast” based on blood flow. Muscle tissue definitely produces bubbles andthis has been known since 1908 and the work of JS Haldane. Dr M P Spencer and I have measured brainbubbles with a Doppler Probe over the sagittal sinus [large vein drain the brain]. Nothing was found.

Dr Deco :doctor:

 

[BRT]

I don't know what is known among people who actually study things but yo-yo profiles make me feel bad afterwards.

 

[_coni_]

Thank you very much all for your detailed answers. To summarize what has been said so far:

- it seems that DCS incidence is not higher for yo-yo dive than for a dive at the envelope of the yo-yo dive (for low-depth, no-decompression diving, slow enough ascents, no data for higher depth or decompression diving).
- the findings of the HSE paper (which are purely based on a model anyway) about brain damages are probably unsubstantial.
- the HSE paper confirms that the common bubble decompression algorithms do not give an intrinsic penalty for yo-yo profiles, which is not surprising considering that these models are not calibrated using yo-yo profiles.

I have a few more questions then, if you would be kind enough to give me a bit more of your time:
- do you know where does the common idea that yo-yo dives are DCS-prone come from?
- are there elements (suspected mechanism) that could lead us to think that yo-yo profiles are risky in *decompression* dives, provided one never exceeds the ceiling of a bubble model?

Thank you again, it's a pleasure to read a forum with such knowledgeable contributors.

 

[TONY CHANEY]

Very well written report and nice screenshot Doctormike. Do you feel that it was the returns to the surface without a safety stop and not waiting on the surface prior to heading back down several times that created the DCS? But then again we all have seen OWI go up and down the line several times when teaching CESA. I know that there were other factors such as cold water and humping heavy gear pre and post dive. I have done a lot of searching pertaining to yo-yo profiles with very little results. What sparked my interest in these profiles was the caves where you can be at the surface then to 60, back up to 30, back down to 63, back up to 25 then surface in a sink and then do it all again returning back to the point of entry. (Think Orange Grove to Challenge). We always do a safety stop and after surfacing spend quite a bit of time on the surface of the sink before heading back.

I was watching a video on freediving and found it very interesting that after every dive, the diver spends twice as much time on the surface as his total dive time.

 

[doctormike]

Very well written report and nice screenshot Doctormike. Do you feel that it was the returns to the surface without a safety stop and not waiting on the surface prior to heading back down several times that created the DCS? But then again we all have seen OWI go up and down the line several times when teaching CESA. I know that there were other factors such as cold water and humping heavy gear pre and post dive.

Thanks, glad you like it! I do think that this was an example of bubble pumping (although waiting on the surface, if anything, would probably have promoted even more bubble growth). My first two ascents were from deeper than typical CESA depth, though, and with more prior nitrogen loading than an OW instructor would probably have doing that skill in a class setting.