To Dr. Deco: Pelagic vs. Suunto algorithms?

[leadweight]

Dr Deco once bubbled...
Dear Readers:

Conservative Computer Algorithms

Do conservative protect you better from DCS. Not really. Why? Because the incidence of DCS is so low as to make analysis impossible.

RGBM computers will not really show much difference if one performs only recreational diving. The microbubble question plays little role in this case. A little difference appears and is why divers say that they are conservative. Possibly, they are too conservative. DCS is not cause solely by gas loading but also by micronuclei generated by physical activity.


http://wrigley.usc.edu/hyperbaric/advdeco.htm

Dr Deco :doctor:

I am glad that this analysis on conservative computers is comming from you, Dr. Deco, because nobody around here would believe it if I said it. I agree 100%. The same analysis would appear to be appropriate for some other scuba urban ledgends.

The RGBM computer thing bugs me a bit, at least as far as the Suunto computers go. I have this hunch, based on a lot of posts some of the technical divers have made around here about the shortcommings of computers for deco stop diving, that Suunto's application of RGBM does nothing in particular for divers going beyond the NDL's other than to cause them to be last to arrive for lunch.

What I think some of the tech divers are saying, and I don't know exactly why this works, is that the deco stops should be distributed over various depths. Perhaps the idea is to slow the ascent and the offgassing process. Based on the limited data from the German magazine it would appear that Aladin computers do that, but Suunto computers go for a very long stop at 3 meters. From experimenting with software like V-Planner (and I don't pretend to know all of the implications of using that program) it seems that it distributes the stops over a wide depth range.

From all of this it would appear that a fairly "liberal" computer like the Pelagics would work fine for a recreational diver. What would work best for a deco stop diver is a more difficult question given the much smaller number of data points. Many divers point to the Bikini Island website where the local dive operator has experience with repetitive dives to 170 feet. They like several meters (especially the Nitek 3) that allow for gas switching because they switch from air to 75% oxygen at 5 or 6 meters. Also acceptable are Aladins and Seiko (dive rite/OMS) single mix meters. They don't like Pelagics and Suunto (except for the gas switching Vytec). Of course, they provide no technical discussion or data for their gear choices. Perhaps all of this confusion over meters is why so many of the technical divers around here prefer to rely on tables or programs running on their PC or Palm. At least with these alternatives you can see what you get beforehand.

 

[DivingDoc]

Has anyone looked at differences in microbubbles as detected by Doppler in people using conservative vs. liberal computers?

 

[Dr Deco]

Dear Diving Doc:

Doppler Studies and Bubbles in Animals :mousy:

To my knowledge, no one has studied liberal vs. conservative computers and the bubbles that they form. Generally speaking, as the gas loads increase, the bubble counts will increase. I do not know if this has been tested systematically in humans, but it has been checked in animals. Pigs and rats on titrated profiles showed a progressive increase in bubbles as the gas loads increased. The references below were the first studies and are the only ones to date.

• Powell MR. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring. Aerosp Med. 1972 Nov; 43 (11):1240-4.
• Powell MR. Doppler ultrasound monitoring of venous gas bubbles in pigs following decompression with air, helium, or neon. Aerosp Med. 1974 May; 45(5): 505-8.

It is generally agreed (but by no means is this universal) that bubbles increase as the dive becomes more hazardous, it, the nitrogen “dose” increases.

Bubbles in Humans:scuba:

A paper has recently appear in Undersea and Hyperbaric Medicine that indicates that bubble grades in recreational divers increase as the “dose” increases. It appears to reach a plateau, although this might be a result of the analytical technique which group bubble Grades together. It does not directly parallel some studies in animals. This might be expected since animals can be given larger nitrogen doses and therefore more severe dives. It is also dependent on how the “dose” is calculated. I am not certain that this can be done with the confidence shown by the authors. Knowing them personally, I know they could provide strong arguments for their position, however.

Dunford RG, et al. The incidence of venous gas emboli in recreational diving. Undersea and Hyperbaric Med. 2002; 29(4) 247-259.

Fatigue

It has been argued that fatigue following a dive is the result of subclinical DCS. The idea is intriguing, and I do not really know the answer. I have never looked into this question, personally.

There is divided opinion on the utility of nitrox in mitigating this problem. It has not been the object of any research to my knowledge.

Dr Deco :doctor:

 

[padiscubapro]

leadweight once bubbled...


I am glad that this analysis on conservative computers is comming from you, Dr. Deco, because nobody around here would believe it if I said it. I agree 100%. The same analysis would appear to be appropriate for some other scuba urban ledgends.

The RGBM computer thing bugs me a bit, at least as far as the Suunto computers go. I have this hunch, based on a lot of posts some of the technical divers have made around here about the shortcommings of computers for deco stop diving, that Suunto's application of RGBM does nothing in particular for divers going beyond the NDL's other than to cause them to be last to arrive for lunch.

What I think some of the tech divers are saying, and I don't know exactly why this works, is that the deco stops should be distributed over various depths. Perhaps the idea is to slow the ascent and the offgassing process. Based on the limited data from the German magazine it would appear that Aladin computers do that, but Suunto computers go for a very long stop at 3 meters. From experimenting with software like V-Planner (and I don't pretend to know all of the implications of using that program) it seems that it distributes the stops over a wide depth range.

From all of this it would appear that a fairly "liberal" computer like the Pelagics would work fine for a recreational diver. What would work best for a deco stop diver is a more difficult question given the much smaller number of data points. Many divers point to the Bikini Island website where the local dive operator has experience with repetitive dives to 170 feet. They like several meters (especially the Nitek 3) that allow for gas switching because they switch from air to 75% oxygen at 5 or 6 meters. Also acceptable are Aladins and Seiko (dive rite/OMS) single mix meters. They don't like Pelagics and Suunto (except for the gas switching Vytec). Of course, they provide no technical discussion or data for their gear choices. Perhaps all of this confusion over meters is why so many of the technical divers around here prefer to rely on tables or programs running on their PC or Palm. At least with these alternatives you can see what you get beforehand.

the reason you are seeing the long shallow stops on SUUNTO RGBM is that its not true RGBM.. There is only ONE computer that fully implements RGBM and thats the Explorer.. Suunto incorporates RGBM LIMITING factors folded onto a haldane model.. this makes initial stops slightly deeper and limitations on repetitive dives but still the telltale "tail" of a haldaneon model.. If you don't believe me see the comments BRW (the creator of RGBM)has made about the explorer

RGBM and the new VPM-B come up with very similiar dives the original VPM didn't account for boyle expansion and programs like vplanner used a bunch of hand tweaks to alter the parameters to make the profiles less agressive.

 

[leadweight]

Actually, padiscubapro, I have seen the comments from BRW that you refer to. Too bad the Explorer is a 4 figure dent in the bank account. Perhaps the upcomming Mares RGBM meter will be an improvement over the current crop of devices in its price range.

 

[padiscubapro]

leadweight once bubbled...
Actually, padiscubapro, I have seen the comments from BRW that you refer to. Too bad the Explorer is a 4 figure dent in the bank account. Perhaps the upcomming Mares RGBM meter will be an improvement over the current crop of devices in its price range.

I agree its definately not cheap.. $1200 for stand alone $1300 for cell integrated, but it does also support constant PO2 and trimix...

If you are doin purely recreational dives its overkill. My main point is why the profiles are the way they are... its using a haldane model as its basis instead of a bubble model, RGBM limiting factors dont alter true RGBM profiles as much...

the rgbm model is very computational intensive so high power microcontrollers are necessary.. yor 50 cent cpu isn't going to cut it.. plus BRW charges 5k for the fortran source for his model, not to mention all the time it takes to convert it to a language like c and get it to fit into a microcontroller..

If I remember correctly it took Hydrospace about 1.5 years to get the model working in a state that could be used in a dive computer..

 

[DivingDoc]

I've attached abstracts for some of the references that Dr. Deco sited above and a few others.

Some of the articles seem to contradict others. Or else it depends upon whether you are exercising while breathing gas enriched with O2 or air.

Abstract number 9 is the only one that deals with divers ascending from a dive in water as opposed to airmen or astronauts ascending to altitude in air. But in that study, moderate intermittent exercise seemed to be preventative of VGE.

So I am confused as to how to translate this data into my diving behavior. Is it better to kick more or kick less on ascent or should I use my arms? Or maybe I should exercise more if on Nitrox and less if on air?

Dr. Deco, what practical changes should I make in my diving behavior to prevent problems based on these studies?

 

[Dr Deco]

Dear Diving Doc:

Literature: Decompression and Exercise

The effects of exercise on gas exchange and decompression do indeed depend on when the exercise is performed and what gas is being breathed.

Many of the references do apply to aviators and astronauts and reflect the sponsoring agency (NASA or the Air Force). The interpretations are mine since anyone can read the material. It is in the open literature. What is not contained is the interpretation of additional material not contained in papers (usually because it is not yet published).

Practice: Decompression and Exercise :scuba:

• Altitude Decompression: While breathing 100% oxygen prior to ascent, mild exercise during the prebreathe or strenuous exercise with at lest 60 minutes on minimal activity prior to depress (for microbubbles dissolution). This is not something that scuba divers would be doing.
  
• While on the Bottom: Divers should try to minimize the activity of arms and legs (i.e. the effect on heart rate and the muscle pump). This is reduce gas uptake. Activity is permitted since this is built into the table test program, but strenuous activity (e.g. swimming against strong currents) should be avoided as much as possible.
  
• During the Safety Stops: The diver should move the arms and legs in a bicycling motion. This will promote regional, tissue blood flow without micronuclei formation.
  
• On the Surface: Here the diver should move about in a moderate fashion. While seated, move the arms and legs periodically to promote blood flow. Heavy exercise should be avoided because it will promote the formation of micronuclei. This includes climbing onto the boat with full, heavy gear, climbing ladders on the boat, running, playing volleyball and the like. While the later activities will promote blood flow, they will also promote the formation and growth of microbubbles.

Experience :doctor:

In my experience, this has been found to work to decrease DCS when tested under laboratory conditions. These ides are not universally accepted by all barophysiologists. As with many new concepts, it has its adherents and detractors.

If this needs more clarification, please just post again and ask for an expansion of the murky points.

Dr Deco :doctor:

 

[DivingDoc]

Dr Deco once bubbled...
Dear Diving Doc:

Practice: Decompression and Exercise :
[*] While on the Bottom: Divers should try to minimize the activity of arms and legs (i.e. the effect on heart rate and the muscle pump). This is reduce gas uptake. Activity is permitted since this is built into the table test program, but strenuous activity (e.g. swimming against strong currents) should be avoided as much as possible.

This may not be possible as you sometimes do get into situations where you need to swim against a current.

[*]On the Surface: Here the diver should move about in a moderate fashion. While seated, move the arms and legs periodically to promote blood flow. Heavy exercise should be avoided because it will promote the formation of micronuclei. This includes climbing onto the boat with full, heavy gear, climbing ladders on the boat, running, playing volleyball and the like. While the later activities will promote blood flow, they will also promote the formation and growth of microbubbles.[/list]

This is often also unavoidable. Indeed, though I have not tried it yet, for the diving near here -- the North Carolina wreck sites -- people climb out of the boat, sometimes in 4-5 foot seas on a fin ladder wearing a 100 Al to 120 cu foot steel tank plus a pony bottle. And the depths are usually around 120 feet, and it's not a multilevel dive. You go down to the site, spend your 10-20 min of bottom time (depending on air or nitrox) and come up. Usually there are 2 dives per day like this -- I think with 90-120 min surface intervals.

So what's a diver to do??? In these sorts of circumstances, is there anything you can do to minimise microbubbles or frank DCS within these paramenters??

 

[DivingDoc]

I wrote:

This is often also unavoidable. Indeed, though I have not tried it yet, for the diving near here -- the North Carolina wreck sites -- people climb out of the boat, sometimes in 4-5 foot seas on a fin ladder wearing a 100 Al to 120 cu foot steel tank plus a pony bottle. And the depths are usually around 120 feet, and it's not a multilevel dive. You go down to the site, spend your 10-20 min of bottom time (depending on air or nitrox) and come up. Usually there are 2 dives per day like this -- I think with 90-120 min surface intervals.

Sorry -- I meant "people climb BACK INTO THE BOAT...".