Reverse profiles--pro's & con's

[jbd]

jetblast asked for a new thread on reverse profiles so here goes.

What are the pro's and con's of reverse profiles?

Is it really any different than a standard profile recommendation of doing the first dive deep and others shallower?

Is there research that backs up the recreational diving recommendation of doing deep first?

 

[Rick Murchison]

First of all, recent studies have shown no adverse effects of reverse profiles within the limits of no-decompression limit diving.
That said, the current recommendations from DAN and NOAA are:
(1) No-decompression dives of less than 130 FSW.
(2) No more than 40 FSW difference in the max depth of the dives.
Please note also that, particularly with tables, there is a considerable surface interval penalty to reverse profiles.
Bottom line - reverse profiles within the limits of the tables are ok, but there are some very practical reasons to do your deepest dives first.
Rick

 

[Spectre]

Originally posted by Rick Murchison
Bottomline - reverse profiles within the limits of the tables are ok, but there are some very practical reasons to do your deepest dives first.

I don't remember the full reasons, but it hits into bubble theory, something that I'm barely on the fringe of understanding. Perhaps some of the Dr. Deco crew'll catch this.

Has anyone actually read the proceedings to the Reverse Dive Profiles Workshop? I saw it at a show and I almost picked it up, but I was more interested in spending my money on the in-water recompression workshop proceedings.

-Jeff

[For those that don't know what I'm talking about]

https://www.diversalertnetwork.org/...5200&mscssid=37WXWJ309KCR8PAJ2EU1QXA5R97N5LED

https://www.diversalertnetwork.org/...5100&mscssid=37WXWJ309KCR8PAJ2EU1QXA5R97N5LED

 

[jetblast00]

Thanks jbd

I was particularly interested because just this morning I had read section 8.9.11 in the GUE tech book on reverse profiles (p 99). Basicly, JJ states that there's nothing wrong with them and it's folklore/myth to think that the there is. But... there were no footnotes in that section, so I didn't have another place to immedietly move to for more info.

The last paragraph eludes to the fact that the reverse profiles should, however, be planned based on some of the deco bubble models (VPM and RGBM I'm guessing...) I was curious to hear people's ideas on how these bubble models affected a reverse profile and specific ideas on planning a reverse profile dive in light of them.

Not too much, eh?

 

[rcohn]

Some of the bubble mechanics guys still don't like reverse profiles, the new NAUI RGBM tables prohibit them.

Quick version of the bubble mechanics argument.
1. Your body is filled with stable micronuclei, which are required as seeds for bubbles.
2. Diving deep and rapid descents can crush some of the micronuclei, removing them from your system.
3. Slow ascents limit nuclei growth by minimizing the partial pressure/tension gradient that can drive gas into the nuclei or bubbles. However, there will be some bubble growth on all ascents.
4. These concepts have been supported by gel experiments.

So, if you do a deep dive with a slow ascent you will crush some of the micronuclei on descent, minimizing the distribution that can grow when you ascend. A subsequent shallow dive may cause further growth but with less bubbles because some were removed on the deep dive.

If you do a shallow dive first, few (if any) nuclei will be crushed and all will grow a bit when you ascend. On the following deeper dive, fewer nuclei will be crushed because they grew in size on the previous shallow dive. They remain to grow again on ascent leaving you with more bubbles in your body than if the sequence was reversed.

If Dr. Deco :doctor: was here he would tell you that he doesn't agree with this theory. He believes (check the archives) that new nuclei are so easily generated by muscle action that trying to crush them to lower the distribution will not work.

For the record, I've read part of the Proceeding of the Reverse Profile workshop and will hopefully get back to it eventually. Some of the papers are very interesting

Ralph

 

[Rick Murchison]

My reasons for usually sticking to "deepest first" are strictly practical.
It isn't very complicated - and really has nothing to do with DCS directly, but rather the nature of the Navy tables.
Allow me an example... I want to do two 50 minute dives - one to 40 feet and one to 60 feet. Using the Navy tables, if I do the 60 foot dive first, I can do the 40 foot dive whenever I want to after a 10 minute surface interval. But if I do the 40 foot dive first, I have to wait over seven hours to do the 60 foot dive and stay out of decompression.
That's a pretty practical reason to "do your deepest dive first."
With the advent of computers the "shallow first penalty" is less, but in the simulations I've played with it's still there - nowhere near the magnitude of the tables, but there nonetheless. (Using the Oceanic, for example, the penalty for doing the 40 foot dive first is a bit over an hour and a half vice the seven hours on the tables)
Rick

 

[100days-a-year]

Decompression theory?Jeez... the the way some people discuss it you'de think it was Decompression exact science.Bottom line is than both sides of this discussion can be supported by a body of research and quite a bit of anecdotal evidence .I personally dive deep 1st most of the time.There are times tho..such as staging a dive that necessitates doing shallow first .Bubble theorists use gelatin to describe the effects&growth of micronuclei .Surprise.... humans ain't jelly,they are dynamic organisms comprised of numerous tissues and densities.The penalties levied by most software and computers for reverse profiles make them less desirable to me.As more scientific evidence is discoversd perhaps that'll change.LY has some killer links to various Decompression sites,the tag on this thread will get his attention,maybe he'll put'em up.

 

[Uncle Pug]

Perhaps it is different for NDL even though we all know that there is no such thing (every dive is a deco dive).

Bad news to take a gas load from a deeper dive (where bubbles are present in the venous side) on a shallow dive (where they can become reduced in size and pass over to the arterial side) and then ascend as though you had no deco obligation. Might as well have a PFO.

If I do a shallow dive following a deeper deco dive I must repeat the entire deco of the first dive. Better to do the shallow dive first IMO.

Whatever gas load you have from your first shallow dive gets taken along on the second deep dive and is dealt with on deco.

Course your deco planning software will give you the correct deco schedule for this. Just my understanding of the general principle.

 

[rcohn]

Originally posted by Uncle Pug
Bad news to take a gas load from a deeper dive (where bubbles are present in the venous side) on a shallow dive (where they can become reduced in size and pass over to the arterial side) and then ascend as though you had no deco obligation. Might as well have a PFO.

This is a popular theory that has NOT been supported by 20+ years of doppler ultrasound research. Bubbles passing from venous to arterial circulation would be detectable via doppler ultrasound. Apparently multiple chamber experiments have failed to support this idea. Again Dr. Deco has covered this in his section.

This shows the problem of relying solely on non-scientific sources for your information. For reasons I fail to understand some of the tech diving gurus like to present unsupported unproven theories as if they are established documented scientific fact.

Ralph

 

[Uncle Pug]

Originally posted by rcohn
Bubbles passing from venous to arterial circulation would be detectable via doppler ultrasound.

I suppose you're right....
Unless you're wrong....
Had a friend that detected them with his brain....

"Underserved hit" they said....
"No evidence of a PFO" they said....

Chamber ride cured the paralysis.

But I don't know for sure...
Just repeating what I was taught...
No personal experience...
I haven't been hit myself...