reverse profiles??

[Thalassamania]

Good question!!!

The theory is the deep first and shallower dives to follow. As the deep dives increase the nitrogen levels. Requiring you to SI for a longer time to dissolve from the body. Deep dives are those of deeper than 20M. If you look over dive table for the fun of it. As you read you'll notice the explanation. Deep first shallow to follow.

In your case 14 and 18m is not such a stretch. However other considerations including; Depth, Bottom Time and the Duration of dive(s) in total. Affect the NDL as well.

Have fun diving and enjoy!!!

It has been many years since that advise was considered appropriate and it is no longer considered valid.

 

[aquaregia]

Rubicon only had the abstract but it appears the paper might be summaried as "decompression dives with no decompression have a higher risk of decompression sickness than no decompression dives". Maybe I am missing it but that does not seem to be helpful in deciding to do a reverse profile within table or computer limits.

Ugh, must have been the wrong link. Sorry, I'll try to look it up this evening.

 

[Thalassamania]

I can't get to the page for some reason, but Bubbletrouble linked to it once:

Title: THE RELATIVE SAFETY OF FORWARD AND REVERSE DIVING PROFILES
Authors: McInnes, S
Edmonds, C
Bennett, MH
Keywords: profile
dive
reverse
ONR
decompression
Issue Date: 2005
Abstract: BACKGROUND: A recent workshop recommended that within certain restrictions, and from a decompression perspective, it is not substantially important whether one conducts dives from deep to shallow or shallow to deep. Thus, in multi-level dives, the deeper part of a dive may be performed later in the dive, while repetitive dives may progress from shallow to deep. These are referred to as reversed dive profiles (RDP). The consensus recommendations were made in the absence of experimental data. MATERIALS AND METHODS: We performed two experiments to test these recommendations. We first exposed two matched groups of 11 guinea pigs to a single multi-level diving profile [36msw for 30min, 24msw for 30min,12msw for 30min], one group in a forward progression (FDP), the other in reverse, and compared the incidence of severe DCS using the method of Albano1. Second, we compressed two groups each of 11 guinea pigs to three repetitive dives [30msw for 30min, 20msw for 30min, 10msw for 30 min, surface intervals 15 minutes]. Similarly, one group performed FDP and the other RDP. Again we compared the incidence of severe DCS. A second series of repetitive dives with increased depth and time was required to produce substantial risk of DCS [36msw for 40 min, 24msw for 40 min,12msw for 40 min]. RESULTS: Multi-level exposure: there was no evidence of DCS in any of the animals exposed to the FDP, while six (55percent) of the RDP group exhibited symptoms of severe DCS and ultimately died (P = 0.01). Repetitive exposures: there was no evidence of DCS in the FDP group versus seven (33percent) in the RDP (P=0.01). CONCLUSIONS: Our findings suggest that multi-level and repetitive dives performed in the established forward profile manner are less hazardous than those performed in the reverse profile mode. We believe the recommendations of the workshop should be re-examined. 1. Albano G. Principles and Observations on the Physiology of the Scuba Diver. ONR Dept of Navy. 1970. NOTE: Albano paper - Rubicon Research Repository: Item 123456789/3277

 

[DevonDiver]

The theory is the deep first and shallower dives to follow.... Affect the NDL as well.

Can I have some SPAM please?




I am really, really looking forwards to your forthcoming advertising campaign here.

 

[turnerjd]

Since it was assumed, reverse profiles have not been, and never will be, large scale tested, so everyone is sort of guessing about how reverse profiles might change things. Isolated research results on non-humans can only provide guidance, but since military and commercial have no need to do repetitive dives, and dive computers have made tables (or at least human subject research) obsolete, a firm answer about reverse profiles might never really be known.

<snip>

If dive computer manufacturers were required to sell computer interfaces with dive computers, then we might get some large scale results. As it is now though, the people most likely to do repetitive reverse profiles are tropical guides, who also do a bunch of other things (rapid ascents, multiple dives over multiple days) that increase risk. So when we get bent, and we do get bent, who can say which of the risk factors contributed most?

The problem is that computers are just the number crunchers that calculated in real time with real data the same things as are on the tables, based on the same research. Remember, all the major computer algorithms such as Bühlmann (without all the additional fudge factors like temp) can be bought in table format as well. If the models have not been tested for reverse profiles, what the computer output is based on entirely........ nothing.

All the computer does is it uses the tissue groups and calculates N2 loading based on depth and time. Then continues calculating N2 loading (decreasing) for the same tissue groups during the surface interval, and then carries on calculating when you go diving again. Basically it considers everything continuously with on gassing and offgassing treated equally.

I don't think that any of the algorithms behind the computers have been chamber dived with humans or goats or anything in reverse profiles.

With reverse profiles, the computer is giving you a false sence of security, because it too has had no experimental (and as you say, will never have any) validation.

As others have said reverse profiles were never tested based on certain assumptions of those doing the tests. These might, or might not be correct. Reverse profiles might be safe, and the computer calculated N2 loadings, NDLs etc good on the second dive, but we just don't know, as we have no real experimental data to compare them too.

Jon

PS. As an experimentalist I say lets go explode some goats..............

 

[beanojones]

It's not pigs anymore? The wondeful smells of HTC- Kewalo basin. Feral cats and pigs.

 

[turnerjd]

I don't know!

The instructor that taught me many moons ago had a T-shirt with a picture of a particularly gnarled and bent looking goat with the text:

Unexploded goats are not evidence of a good decompression profile

I always thought that they used goats way back, and then "progressed" to humans and we had pretty much stuck to masochistically compressing our fellow men ever since.

 

[turnerjd]

I also didn't know that HTC- Kewalo did any research. They not treatment only?

Assuming that I have understood right that this is the hyperbaric treatment center in Hawaii, now at the Kuakini Medical Center?

Jon

 

[Tortuga68]

UK Diving Conservation

 

[turnerjd]

Yes, I knew that DERA still did goats, although I didn't know it was for submarine escape research. I have also heard that ocassionally the French do some goat work too.

I didn't know that they were only second choice for Haldane though. Nice interesting article.

Jon