To Dr. Deco: Pelagic vs. Suunto algorithms?

[DivingDoc]

Dr. Deco:

I am aware that the Pelagic vs. Suunto algorithms are different and that the Suunto's are more conservative.

Which algorithm in your opinion is the one that's closer to what actually happens in the body?

And which one do you agree with more (actually, that's probably the same question).

 

[leadweight]

In the computer & guages forum I have a poll going. Over half of those responding use Suunto RGBM computers, about 20% Pelagic. About 25% for all others combined. Oddly, Cochran which lacks the marketing clout of Scubapro/Uwatec, is in third place just ahead of Uwatec.

I don't have a Suunto. It might be features, price, design or the desire to have a more conservative computer, but Suunto is dominating the field.

 

[detroit diver]

I thnk most of it has to do with marketing. They're better at it thank anyone else.

leadweight once bubbled...
In the computer & guages forum I have a poll going. Over half of those responding use Suunto RGBM computers, about 20% Pelagic. About 25% for all others combined. Oddly, Cochran which lacks the marketing clout of Scubapro/Uwatec, is in third place just ahead of Uwatec.

I don't have a Suunto. It might be features, price, design or the desire to have a more conservative computer, but Suunto is dominating the field.

 

[DivingDoc]

leadweight once bubbled...
In the computer & guages forum I have a poll going. Over half of those responding use Suunto RGBM computers, about 20% Pelagic. About 25% for all others combined. Oddly, Cochran which lacks the marketing clout of Scubapro/Uwatec, is in third place just ahead of Uwatec.

I don't have a Suunto. It might be features, price, design or the desire to have a more conservative computer, but Suunto is dominating the field.

Yes, I saw your poll. I also had a poll with the question of which computers were most likely to break down -- Suunto came out the least likely.

I am trying to decide between the Suunto Vytec and the Oceanic VT Pro. We have Oceanic DataMax Pro Plus's and are happy with them, but our kids need computers, so we thought we'd buy new hoseless AI ones for ourselves and give them our current ones.

The VT Pro would be familiar to us, since we are used to the Oceanics we have.

To me the factors in favor of the Vytec are as follows:

-- full deco computer in case I ever accidentally go into deco.
-- More conservative algorithm, and we are getting into the geezer category.
--- Less likely to break down per my poll
--- Probably needs battery changes less often.
--- Better software than the Oceanic stuff
--- greater memory capacity for dives

Against Vytec:

--No N2 loading bar graph, which I think is much more intuitive than simply NDC time remaining given as a number. ( the N2 bar graph changes to an OLF graph when you swith into Nitrox mode)

--- Display is hard to see -- especially, it's hard to see the bar graph in low light.

For Oceanic VT Pro:

--- Nice colorful intuititive display.
--- Has both N2 loading and O2 toxicity graphs displaying all the time, with option to also display actual pO2 level.
--- More like what I'm used to using
__ Less expensive

Against VT Pro:

---Software not as good as Suunto and not as good memory capacity.

---Not sure if it's a full deco computer.

Ah -- decisions, decisions.

 

[leadweight]

Hey Doc:

A few odds and ends:

I don't think that the VT Pro is available for sale yet.

If your heart is set on wireless don't let me spoil the party, but I would rather have $500 in my pocket and an SPG. The Vytec must be paired (witnin a few inches distance) with its transmitter each time the tank valve is turned on. Also, it disconnects after 5 minutes of no pressure change. On some dive boats the staff runs around turning on tanks for you and you may have to turn your tank off, let a bit of air out and turn it on again as part of your regular gearing-up ritual.

Somehow I feel an analog SPG is going to be more dependable than something with a strain guage, battery and digital radio transmitter in it.

Whether a computer is conservative is relative and a lot depends on exactly where the comparison is made along the time and depth curve.

Some tests in a German magazine (you may have seen the summary in the computer & guages forum) actually showed a dive sequence where the Pelagic/Aeris required a longer stop time than a Vyper. Most divers in the US tend to avoid going past the no-stop times. In this respect the Pelagics seem more liberal. Europeans are much more likely to run up modest deco stop obligations in which case the Vyper could require a shorter stop. I suspect this explains Diver magazine's usually lukewarm reviews of Pelagic computers.

There appears to be another big divergence between Suunto and Pelagic on a 70 foot second dive one hour after a 100 foot dive with both in the no stop limits. This was shown in the graphs published in Rodale's. As the divers gradually surface the Pelagic clears to a long NDL at 40 feet the Suunto must go much shallower. I believe this, and not a defective Pelagic computer as some have theorized, was the cause of the large discrepency between the Pelagic and other brands of computers tested by Diver magazine.

The fact of the matter is, meter manufacturers give relatively little information as to how their products will behave other than for the no-stop limit on a first dive.

To summarize, as a non-expert consumer/diver I don't think either of these brands of meters are bad, but they sure behave differently

 

[DivingDoc]

leadweight once bubbled...
Hey Doc:

A few odds and ends:

I don't think that the VT Pro is available for sale yet.

My LDS just got their first one in.


Where are the reviews you're talking about with graphs in Rodale's? Do you know the URL?

 

[leadweight]

http://scubadiving.com/gear/022003computers/

http://scubadiving.com/gear/022003computers/images/200302GR_17_dive2.gif

Diver Magazine:

http://www.divernet.com/equipment/0602divertests.htm#versa

Summary of the German tests:

http://www.scubaboard.com/showthread.php?s=&threadid=26271&perpage=15&display=&pagenumber=3

A lot of information & no real answer. One would think they would not be so different.

So....how did the VT Pro look to you? Kind of like a Versa Pro with tank pressure and air remaining time?

If you are willing to live with a feature set that is more limited, the Aladin Air Z Nitrox is fairly cheap mail order.

 

[Dr Deco]

Dear Readers:

Editorial

Some questions and replies have appeared concerning computer algorithms. They concern which is better. I do not really know. I have known many modelers of decompression in my day, and they all share the characteristic of believing in their model. I suppose that simply makes sense.

When I read some of the assumptions upon which the models and algorithms are based, I think to myself, physiologically this is incorrect. Yes, the program will result in a successful decompression, but not for the reason given. When divers then compare two deco meters, they are perplexed by the fact that the two yield different answers. The assumption is that there is only one correct answer, that this will be true for all divers, and this will hold day after day. With a modicum of reflection, most divers would answer, “No, this uniformity does not really exist.”

The difference in tables and meters derives from the concept that supersaturation alone is the responsible agent for DCS. This is incorrect. DCS requires both supersaturation and tissue microbubbles. Some aspects of microbubble concentration are contained in certain algorithms, but they exclude the activity-generating nuclei formed during the surface interval. I have not yet figured out how to incorporate this activity into my mythic Bends Buster deco meter, or I would build it and put it on the market.

In the great spectrum of decompression times, a few minutes between meters is nothing. That is derived solely from the NDLs used by the designer.

It is difficult to believe how much musculoskeletal activity affects DCS risk until you see it in controlled, laboratory studies. We encounter it all the time at NASA.

Dr Deco :doctor:

 

[DivingDoc]

Dr Deco once bubbled...

It is difficult to believe how much musculoskeletal activity affects DCS risk until you see it in controlled, laboratory studies. We encounter it all the time at NASA.

Can you describe the laboratory experiments -- were they with humans or animals and exactly what was the protocol, etc.

It makes perfect sense to me that exercise would affect it. Think about the difference between what happens with a bottle of pop if you open it after shaking it up vs. opening it after it's been sitting undisturbed.

I found a really good website that explains the RBGM algorithm:

http://www.rgbm.mares.com/html/eng/rgbm/video.asp?id=8&lang=eng

I think the videos are especially helpful.

Dr. Deco -- what do you think about the concept of doing a rapid descent after a surface interval (at least 66ft/min) in order to "crush" the microbubbles.

ET

 

[Dr Deco]

Dear DivingDoc:

Study Data for Exercise

Some of this work is currently in progress and is not written up. I am simply citing what has been observed in recent months. Later it will be published.

Othr parts are older and the easiest way to access the original studies (ARGO series, initiated in 1989) is at the web site connected to this Scuba Source Forum. It is available at

http://www.doctordeco.com

Some other material is not in journals and thus will not be cited.

Strenuous Activity and DCS

Dervay JP, Powell MR, Butler B, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med. 2002 Jan; 73(1): 22-7.

Conkin J, Powell MR. Lower body adynamia as a factor to reduce the risk of hypobaric decompression sickness. Aviat Space Environ Med. 2001 Mar; 72(3): 202-14.

Mild Activity and Gas Washout

Loftin KC, Conkin J, Powell MR. Modeling the effects of exercise during 100% oxygen prebreathe on the risk of hypobaric decompression sickness. Aviat Space Environ Med. 1997 Mar; 68(3): 199-204.

Jankowski LW, Nishi RY, Eaton DJ, Griffin AP. Exercise during decompression reduces the amount of venous gas emboli. Undersea Hyperb Med. 1997 Jun; 24(2): 59-65.

Webb JT, Pilmanis AA, Fischer MD, Kannan N. Enhancement of preoxygenation for decompression sickness protection: effect of exercise duration. Aviat Space Environ Med. 2002 Dec; 73(12): 1161-6.

Wisloff U, Richardson RS, Brubakk AO. NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats. J Physiol. 2003 Jan 15; 546 (Pt 2): 577-82.


Dr Deco :doctor: