Reverse Profile?

[TMHeimer]

Everyone knows you plan the deepest dive of 2 or more first. I've read that from a model point of view there's no mathematical reason for this recommendation, but the large body of existing test data involves forward profiles. I'm curious as to why there hasn't been many (any?) testing of reverse profiles.

 

[Gene_Hobbs]

In 2002, The Office of Naval Research tasked UHMS with performing a comprehensive analysis of the Navy's research and development program in Undersea Medicine. The panel found that 60% of the young researchers in the field left within less than ten (10) years. Additionally, it was discovered that many of the senior scientists in this arena would retire in the near future (52% retiring in less than 10 years and 96% retiring in less than twenty years). Further, the Navy had not trained any investigators in the previous ten (10) years. This turnover in researchers and the loss of senior scientists potentially signifies a great loss in human knowledge that can be transitioned to new researchers.

Funding for undersea work is a MAJOR reason for the loss of young researchers. Navy funding dollars have not really changed since the early 1980's and commercial diving companies have all but stopped funding new research as there is no perception of a need for more work.

So, that's the why new things have not been done... (And the MAJOR reason why we decided to start Rubicon. We saw a need to preserve the knowledge, use the resources and fund more work. We are finally starting to use the research for some of our own projects this year. Given the drop in the economy, it will likely be a LONG time before we will be able to find enough funding to support other projects)

As for the work that does exist... The Reverse Dive Profiles Workshop has some great articles and inspired some work to be done in this area.

FINDINGS: 1. Historically neither the U.S. Navy nor the commercial sector have prohibited reverse dive profiles. 2. Reverse dive profiles are being performed in recreational, scientific, commercial, and military diving. 3. The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any definite diving experience that indicates and increased risk of DCS. 4. No convincing evidence was presented that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS. CONCLUSIONS: We find no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw).

Lang, M.A. & C.E. Lehner (eds) 2000. Proceedings of Reverse Dive Profiles Workshop. Smithsonian Institution, Washington D.C. 295p. RRR ID: 4244

Since then, a few other projects have been published including this one:

McInnes, S; Edmonds, C; Bennett, MH. The relative safety of forward and reverse diving profiles. Undersea Hyperb Med. 2005 Nov-Dec;32(6):421-7. RRR ID: 4059 Followed by a "Letter to the editor" from Risberg on the work. RRR ID: 5008

Good luck with you search for more information!

 

[Hallmac]

Everyone knows you plan the deepest dive of 2 or more first. I've read that from a model point of view there's no mathematical reason for this recommendation, but the large body of existing test data involves forward profiles. I'm curious as to why there hasn't been many (any?) testing of reverse profiles.

What have you been reading?

Mathematically, you can prove it is possible to walk through a solid object. From all that I have studied, while nitrogen absorption is mathematically the same, the level of absorption the tissues handle is generally accepted. Half tissue levels is what most tables and computers base their dive times upon. Remember it is not the rate of absorption that they are watching, it is the level that each type of tissue is holding and the rate it absorbs and releases the gas.

By loading the tissues even with a small amount at first, you still shorten the time that you reach saturation. That means you have a shorter bottom time at the deepest depth. Remember this applies to no-decompression recreational diving.

Reverse profiles have been studied, published, and discussed many times. I have a few I use to discuss the application theory in class all the time.

 

[ivobj]

Interesting subject...

I agree with you that a lot more testing is made with forward profile, but there is some (although less) tests with reverse profile as well.

Basically the conclusions point to what you mentioned, that there is no point in recommending so strongly agaist reverse profile for recreational diving. What was found by the few tests I could find is that within NDL there are no bigger risk of DCS than for forward profile, provided that of course, you respect max botton time on the second dive, which shall be a lot shorter if you make the deeper dive as your second one. For decompression dives nevertheless, using bubble model as a base for study (Bruce Winke's RGBM, David Yount's VPM, Duke University bubble-volume model and DCIEM bubble evolution based on dopler scores), there was some results that actually pointed out for a higher risk of DCS for decompression models.

I put a transcript below of the final conclusion of this study, which was published in a article that appeared in Pressure, the newsletter of the Undersea & Hyperbaric Medical Society, Inc. (Volume 29, Number 2 2000 March/April), written by R. W. Hamilton and Erik Baker.

QUOTE
Neither the U.S. Navy nor the commercial sector has prohibited reverse dive profiles, and they are performed in recreational, scientific, commercial, and military diving. Since the prohibition of reverse dive profiles cannot be traced to any definite diving experience that shows an increased risk of DCS and no convincing evidence was presented that reverse dive profiles within the no-decompression limits lead to a measurable increase in the risk of DCS, the workshop participants found no reason to prohibit reverse dive profiles for no-decompression dives less than 130 fsw and depth differentials less than 40 fsw.
UNQUOTE

 

[speleodiver6]

Funding for undersea work is a MAJOR reason for the loss of young researchers. Navy funding dollars have not really changed since the early 1980's and commercial diving companies have all but stopped funding new research as there is no perception of a need for more work.

So, that's the why new things have not been done... (And the MAJOR reason why we decided to start Rubicon. We saw a need to preserve the knowledge, use the resources and fund more work. We are finally starting to use the research for some of our own projects this year. Given the drop in the economy, it will likely be a LONG time before we will be able to find enough funding to support other projects)

As for the work that does exist... The Reverse Dive Profiles Workshop has some great articles and inspired some work to be done in this area.



Lang, M.A. & C.E. Lehner (eds) 2000. Proceedings of Reverse Dive Profiles Workshop. Smithsonian Institution, Washington D.C. 295p. RRR ID: 4244

Since then, a few other projects have been published including this one:

McInnes, S; Edmonds, C; Bennett, MH. The relative safety of forward and reverse diving profiles. Undersea Hyperb Med. 2005 Nov-Dec;32(6):421-7. RRR ID: 4059 Followed by a "Letter to the editor" from Risberg on the work. RRR ID: 5008

Good luck with you search for more information!

Thank you Gene!!

That is one more reason to keep contributing to Rubicon, green on its way!!

Now back to lurking...

Dive safe,

Celia

 

[TMHeimer]

I found the reference that there is no mathematical reason for the recommendation to avoid reverse profiles in the PADI DM Manual.

 

[Crowley]

I found the reference that there is no mathematical reason for the recommendation to avoid reverse profiles in the PADI DM Manual.

There is a very good mathematical reason, but no sound physiological evidence that reverse profiles are more likely to predispose you to DCS. Mathematically speaking, try using the RDP (or any dive table) to plan a shallow dive followed by a deep dive within a recreational dive day. You will not find it easy to do so. Some research by DSAT and DAN (I think, I need to go look that up) suggests that reverse profiles are actually beneficial in terms of reducing the risk of DCS. Some research (by Suunto, for example) disagrees.

Research and testing is out there - it's just not always easy to find and often very complicated - and inconclusive. The truth is, nobody really knows if reverse profiles are good or bad. From personal experience I can tell you that when I put a guy in the chamber last year the doctor insisted it was because his first dive (26 metres) was 2m shallower than his second (28m). On the other hand, I've done hundreds of reverse profiles whilst working, with no ill effect. So that doesn't really help either!

I've read a fair bit on the subject (I am no expert, though) and my personal conclusion is that if you're diving sensibly, within conservative recreational dive limits, then the theoretical rights and wrongs of reverse profiles are fairly academic. Much more important is staying within depth, time and no decompression limits, avoiding sawtooth profiles (which are definitely bad), ascending slowly and making safety stops.

Safe diving folks,

C.

 

[Teamcasa]

Everyone knows you plan the deepest dive of 2 or more first. I've read that from a model point of view there's no mathematical reason for this recommendation, but the large body of existing test data involves forward profiles. I'm curious as to why there hasn't been many (any?) testing of reverse profiles.

There is always more need for testing in our sport. It is just too bad that getting the funding to conduct these tests is so difficult.

I applaud those that take this research seriously enough to dedicate their careers and lives to it.

 

[nilsdiver]

Much more important is staying within depth, time and no decompression limits, avoiding sawtooth profiles (which are definitely bad), ascending slowly and making safety stops.

Hmmm, Any one have a good definition for why and when a sawtooth profile is bad? Specifically how many "teeth" in what time frame, and what the pressure (depth) change of a "tooth" has to exceed to count? Basically how much up and down does it take to become a risk?

 

[spectrum]

Hmmm, Any one have a good definition for why and when a sawtooth profile is bad? Specifically how many "teeth" in what time frame, and what the pressure (depth) change of a "tooth" has to exceed to count? Basically how much up and down does it take to become a risk?

The bad part of the sawtooth is as always the ascent. Just as a fast ascents can leave you fatigued and perhaps with sub clinical DCS or worse the repeated ascent within a profile can have a similar cumulative effect as you repeatedly on and off gas. A sawtooth profile stresses the algorithm a computer is running and is beyond the scope of table diving. All things considered I doubt that there is a definitive answer to how much is bad. perhaps I'll learn otherwise.

The key to managing your profile is one of rate and magnitude. Any ascents want to be made deliberately and you don't want to on excursions form the surface to the bottom. As an example, on a local shore dive to 40 feet I do not think twice about following a bottom contour that may have ledges rising 10 feet. My profile when plotted will is segments look more like a kiddie roller coaster than a sawtooth though.

Pete