Reverse Dive Profiles

[Mario S Caner]

It's been over a year since the the findings and conclusion of the Smithsonian Institutions Reverse Dive Profiles Workshop has been published.

For those of you who aren't aware of the findings:

* Historically, neither the U.S. Navy nor the commercial diving sector has prohibited reverse dive profiles.

* Reverse dive profiles are being performed in recreational, scientific, commercial and military diving.

* The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any definite diving experience that indicates an increased risk of DCS.

* No convincing evidence that reverse dive profiles within the No-deco limits lead to a measurable increase in the risk of DCS was presented.

The Conclusion:

* The workshop found no reason for the diving communities to prohibit reverse dive profiles for no-deco dives less than 130fsw and depth differentials less than 40fsw.


I first read about the above back in February, and I beleive in the results due to the credibility of the participants. Though, I now know better, I still find it difficult to break the code of rules that's been etched into my brain through the years.

In fact I still teach (obviously) 'the deepest dive first' rule. I have to, because the trainig agencies say I have to. There is no leeway in that... even mentioning to the contrary would no doubt get me in a world of trouble.

The advent and introduction of dive computers, and the continuos evolution of the technology, has given us an incredible amount of freedom. It's not that we can do anything extrordinarily different than what we were able to do 20 years ago... it's just that now, we can keep ourselves better informed and therefore dive safer.

Though we may not be able to say it's safer to dive the deepest dive first, we can emphasize the practicality that comes with it. For those of you whom have dive computers that have pre-dive profiling abilities, you will see that by diving to 40fsw for 60 min, then a 1 hr surface interval followed by a 100fsw dive for 20min will require a rather lengthy multi stop deco requirement. Do it the way you were taught in class and there is no mandatory deco requirement.

Any opinions?

Mario

 

[Walter]

Mario,

I started teaching SCUBA in 1986 progressing through Instructor Trainer and I'd never heard of that "rule" until I saw posts that it wasn't valid. I always recommended the practice since it dramatically increases your bottom time. How much it increases your bottom time varies from dramatically with YMCA tables to slightly with the Bend a Friend tables. When was it instituted as a "rule"? and by what agency(ies)?

Over the years, I've tried to keep reverse profiles at a minimum because of bottom time considerations, but I've made them when the situation suited me.

Walter

 

[rcohn]

I'm slowly (very slowly) working my way through a copy of the proceeding of the workshop. While I will do a reverse profile, I avoid them when possible. Deepest dive first provides more bottom time. Also, it is my understanding that the bubble theorists were not in full agreement which led to the 40 ft restriction. Rapid descents followed by slow ascents produce the minimum expansion of the existing micronuclei. Deep dives may crush some micronuclei. Doing a shallow dive first could add gas to the existing nuclei, preventing their destruction on the later deeper dive which would expand them further on ascent. Reverse profiles therefore might tend to increase the size/number of silent bubbles in the body. This concern is based on theory and gel experiments. Bubble size and distribution is very dependent on how the profiles are conducted.

Hopefully Dr. Deco may comment further.

Ralph

 

[Mario S Caner]

Walter,
I beleive the rule in question first made it's way into the PADI Instructor's manual in 1972. It stated :"One very important rule - WE ALWAYS MAKE OUR DEEPEST DIVE FIRST when using the dive tables" No rationale was provided as to where the rule originalted, but examples were given clearly showing the advantages of making the deepest one first.

A book published by Dr Chris Dueker in '78 'Scuba Diving Safety' recommended the deep first rule.

By the '80's the recommedation became a rule and is clearly outlined in the PADI, NAUI, SSI, SDI etc manuals. Those agencies combined, represent the bulk of the diving planet. It's been etched into just about every new divers brain. Students often repeat 'I will always dive my deepest dive first' Along with 'I will never-ever-ever hold my breath while diving'. The bad one's get to write it on the dry erase board a thousand times...

 

[jenmichigan]

Mario,

As far as opinions go here's mine. Not doing your deepest dive first is like driving the car backwards down the road. I want to be at my best physically and mentally on the deepest dive of the day. Also any number of problems could occur which would lengthen the dive for some reason. At shallow depths lengthening the dive doesn't matter as much as it does at 100'. I want to know that the deep dive has been done for a specific amount of time - period. Then I can plan my shallow dive without worry.

Just my opinion,
Jennifer
http://www.MichiganShipwrecks.com

 

[Dr Deco]

Dear FORUM Readers:

The idea of “deepest first” was introduced to me through the idea of tissue microbubbles several decades ago. I do not know of the period of origin of this concept, but do know that it was connected to the idea of crushing and eliminating the tissue nuclei so that they would not grow on further dives.

It is my general feeling that this idea came from observations of Hawaii pearl divers whose decompression (or lack of it) was the object of considerable conjecture within the scientific community. The favored opinion was that these divers made deep dives early in the day and shallower ones thereafter. The hypothesis (and it made eminent sense) was that micronuclei were crushed – and did regrow to a large diameter during the remainder of the day’s activities if you stayed shallow. Additionally, we had the concept that nuclei would grow during one shallow dive/decompression cycle and be carried over into the next deeper cycle. Thus, a shallow dive would provide “seeds” for the next crop of decompression gas bubbles of a deep dive.

An analysis of dive data by the group at the Smithsonian Institution was that there was little evidence that this scenario was anywhere true. It did not appear that with shallow-to-deep, calamity and misfortune would surely follow you all the days of your life.

The fact is micronuclei appear to be generated rather easily and, while they may be crushed to some degree, they are easily reformed during the “work of walking” during the surface interval. This growth was mentioned in the “Running and Diving” question asked a day or two ago by a reader. (The fact that you do not walk in space [0-g] is the reason that NASA oxygen prebreathe schedules for EVA were investigated in the laboratory and revised.)

During the chamber tests for the “Recreational Dive Planner,” we performed some trials with shallow-to-deep dives without any noticeable change (i.e., increase) in Doppler bubbles compared with deep-to-shallow dives. However, since “common wisdom” was against this practice, the lab schedule was revised so that only deep-to-shallow was tested during the major portion of the program.

Why does it not appear that shallow-to-deep is bad? It is my feeling that the answer lies in regeneration of tissue micronuclei during the activity in the surface interval. Thus, any nuclei that you might loose in the first compress/depress cycle will be reformed during you normal surface activities and walking about. Much is probably regained simply by climbing the ladder during reboarding the dive boat. If this hypothesis is correct, then obviously the order of the dive is irrelevant, and the interdive activity is more relevant. This activity, as I have stated on several occasions in this FORUM, should involve limb movement but not straining or heavy lifting with arms, legs, or spine.

 

[Narcosis1]

We all have a few of these, lol

Yet there are a few with huge saw tooth profile such as camera men etc. This must follow the same principles of reverse profile diving.

If not worse. Although I do not practice reverse profile diving, I have yet to meet someone who has been bent by doing reverse profile diving.

Whatever practice its always wise to be conservative on your last dive of the day. Safe prctises etc.

 

[Rick Murchison]

Reverse profiling for recreational divers rarely makes good sense simply because, even with a computer, you lose valuable bottom time... As an instructor I often find that I have to make deeper dives the same day I've started shallow, but when I put on my recreational hat, and I'm diving for my own pleasure, I plan the deepest first simply because I can spend more time blowing bubbles that way.
Rick

 

[rcohn]

Dr Deco,

I wanted to ask a followup question regarding your comment,

Why does it not appear that shallow-to-deep is bad? It is my feeling that the answer lies in regeneration of tissue micronuclei during the activity in the surface interval. Thus, any nuclei that you might loose in the first compress/depress cycle will be reformed during you normal surface activities and walking about. Much is probably regained simply by climbing the ladder during reboarding the dive boat. If this hypothesis is correct, then obviously the order of the dive is irrelevant, and the interdive activity is more relevant. This activity, as I have stated on several occasions in this FORUM, should involve limb movement but not straining or heavy lifting with arms, legs, or spine.

I was wondering about the distribution of the reformed micronuclei. It would seem that an activity such as walking would create micronuclei in the joints from tribonucleation and prehaps in the muscles. I've heard speculation that the damaging nuclei are more likely to come from the lipid tissues or in/around nerves such as the spinal column. Do you have any thoughts on how micronuclei distribution would affect the risk of DCS?

Thanks.

Ralph

 

[King_Neptune]

This post kinda got buried in another forum so I thought I would move it to Dr Deco's forum since it was re-asked and Dr Deco answered it In This Thread in case someone was following it and wanted to know. (I will close this thread so people dont get confused by someone replying to this one)


=-)