Part 4: Deep stops

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Ya, I thought that the article would speak for itself. Here are some points worthy of looking at:

"It is not my intent to re-litigate the previous three sections of this article, but an interesting, and I believe, underappreciated aspect of Brian Hills’ pearl diver study provides a nice segue. What I find most interesting are the roughly 3,000 deaths and injuries of an unknown quantity that helped shape those unique ascent profiles. In other words, how was this conclusion affected by the elimination of those who are more susceptible to injury, and how much was due to a lack of rigor in the study ?"

In essence the quantitative experience of pearl divers pleads in favor of deep stops as opposed to quantitative experience of US Navy tables, which is in favor of dissolved gas limits.

"By far the most useful part of decompression research has been the accumulation of data and the refinement of algorithms that capture these outcomes. Ideally, these algorithms would extend well beyond the data they describe, supporting “safe” diving profiles where sparse or even no data exists. Yet, evidence suggests that our models are especially bad in these outlier territories including very deep and/or very long dives. Most divers with meaningful experience in the 100+ meter range will admit they have little assurance of a clean ascent absent any symptoms of decompression sickness. These aspects further suggest that we are working in the proverbial dark, or at least just barely within the distant illumination of modern knowledge. This appears true at least with respect to specific determinations of cause (mistakes made) and effect (DCS incidence). Attempts to manage this uncertainty are in process among researchers spanning the globe."
 
Current and foreseeable models may not be describing any sort of truth, but they do appear good at determining useful boundaries (time and depth limitations) around which a desired outcome (limited DCS risk) appears most likely. I do not mean to belittle that success in the least. We maintain a high degree of confidence we will not suffer decompression sickness on most dives, and that is no small achievement.

I approve this message.
 
In essence the quantitative experience of pearl divers pleads in favor of deep stops as opposed to quantitative experience of US Navy tables, which is in favor of dissolved gas limits

Captain Sinbad,

You are perpetrating a myth. Did your read the link in Jarrod's article which is to an extract in a book chapter in which David Doolette and I cite the data that you believe "pleads in favor of deep stops"?

Here is what it says:

“The few studies available at the time of adoption of deep stops by technical divers [53,55] have been interpreted to support this notion. The earliest of these papers, an observational study of the practices of pearl divers in the Torres Strait of Australia [53], often cited as unqualified support for deep stops, is difficult to obtain and worth summarizing here. These pearl divers performed air dives to depths up to 80 msw followed by empirically-derived decompression schedules that had deeper stops and were somewhat shorter than accepted navy decompression schedules. Thirteen depth/time recordings were made of such dives, and these dives resulted in 6 cases of DCS (46% incidence). The remaining data was a count of dives performed from four fishing vessels over a two month period and these 468 man-dives resulted in 31 reported cases of DCS (7% incidence). It takes a certain cognitive dissonance to interpret these high incidences of DCS as supporting a deep stops approach.”

In: Feletti F, editor. Extreme sports medicine. Basel: Springer International Publishing; 2016. p. 313-33.


It is hardly a ringing endorsement for the pearl divers' deep stop approaches.

Jarrod's fundamental approach to this discussion is, I believe, flawed. He maintains a deeps stop vs shallow stop perspective, but the truth is every decompression has to have its deepest stop and in that sense we all believe in deep stops. The thing we wish to try to avoid is making our deepest stops too deep for optimally efficient decompression. The point indicated by the currently available data is that bubble models and at least one ratio deco approach impose deepest stops that are too deep for optimally efficient decompression. That's it. In espousing a position in which you are either for deep stops or against them one could encourage a (potentially risky) belief among the 'against group' that endlessly shallower stops may be better, but that has never been the message.

Simon M
 
Captain Sinbad,

You are perpetrating a myth. Did your read the link in Jarrod's article which is to an extract in a book chapter in which David Doolette and I cite the data that you believe "pleads in favor of deep stops"?

Here is what it says:

“The few studies available at the time of adoption of deep stops by technical divers [53,55] have been interpreted to support this notion. The earliest of these papers, an observational study of the practices of pearl divers in the Torres Strait of Australia [53], often cited as unqualified support for deep stops, is difficult to obtain and worth summarizing here. These pearl divers performed air dives to depths up to 80 msw followed by empirically-derived decompression schedules that had deeper stops and were somewhat shorter than accepted navy decompression schedules. Thirteen depth/time recordings were made of such dives, and these dives resulted in 6 cases of DCS (46% incidence). The remaining data was a count of dives performed from four fishing vessels over a two month period and these 468 man-dives resulted in 31 reported cases of DCS (7% incidence). It takes a certain cognitive dissonance to interpret these high incidences of DCS as supporting a deep stops approach.”

In: Feletti F, editor. Extreme sports medicine. Basel: Springer International Publishing; 2016. p. 313-33.


It is hardly a ringing endorsement for the pearl divers' deep stop approaches.

Jarrod's fundamental approach to this discussion is, I believe, flawed. He maintains a deeps stop vs shallow stop perspective, but the truth is every decompression has to have its deepest stop and in that sense we all believe in deep stops. The thing we wish to try to avoid is making our deepest stops too deep for optimally efficient decompression. The point indicated by the currently available data is that bubble models and at least one ratio deco approach impose deepest stops that are too deep for optimally efficient decompression. That's it. In espousing a position in which you are either for deep stops or against them one could encourage a (potentially risky) belief among the 'against group' that endlessly shallower stops may be better, but that has never been the message.

Simon M

I was expressing Jarrods thoughts in my words. That is not my view at all.
 
Ya, I thought that the article would speak for itself. Here are some points worthy of looking at:

"It is not my intent to re-litigate the previous three sections of this article, but an interesting, and I believe, underappreciated aspect of Brian Hills’ pearl diver study provides a nice segue. What I find most interesting are the roughly 3,000 deaths and injuries of an unknown quantity that helped shape those unique ascent profiles. In other words, how was this conclusion affected by the elimination of those who are more susceptible to injury, and how much was due to a lack of rigor in the study ?"

In essence the quantitative experience of pearl divers pleads in favor of deep stops as opposed to quantitative experience of US Navy tables, which is in favor of dissolved gas limits.
I was expressing Jarrods thoughts in my words. That is not my view at all.

Except that's not what is says.

If you kill or maim thousands of your diver population (which is finite in the case of the pearl divers), then sure those who are left - they can pretty much "decompress" any old way. The only divers left are the hyper offgassers. They are the worst population to try and extrapolate to a broader body of <all divers>
 


Except that's not what is says.

If you kill or maim thousands of your diver population (which is finite in the case of the pearl divers), then sure those who are left - they can pretty much "decompress" any old way. The only divers left are the hyper offgassers. They are the worst population to try and extrapolate to a broader body of <all divers>



"Hills concluded that the success of the profiles was “due to the much deeper initial decompression stops used” by the pearl divers. In a similar way, technical divers took note of the history, the encouragement from experts, and the perceived success by those in their community.

Given new and mounting evidence against deep stops, can we now definitively conclude that Hills, the pearl divers, and the tech divers were wrong? Are we sure the perceived success was imagined? If some success occurred, was it more about the generally low levels of risk in decompression sickness? Or could something else worth considering be at play? Asked another way, we might inquire how the conclusions reached by Hills and those technical divers are different from the way modern-day decompression tables have come into being." JJ
 
"... can we now definitively conclude that Hills, the pearl divers, and the tech divers were wrong? " JJ

I'd just say it's probably time to listen to, rather than ignore, the data :). Cited studies below were lifted from posts somewhere by Dr. Mitchell.

Pearl Diver Data:

"Thirteen depth/time recordings were made of such dives, and these dives resulted in 6 cases of DCS (46% incidence). The remaining data was a count of dives performed from four fishing vessels over a two month period and these 468 man-dives resulted in 31 reported cases of DCS (7% incidence)."

NEDU study:
One dive decompressed according to a US Navy bubble model and the other according to a US Navy gas content model. ~200 dives on each profile with a significantly higher incidence of clinical decompression sickness (DCS) on the bubble model profile.

Spisni study: comparing UTD ratio deco (RD) and GF 30/80. The study imposed a significant inbuilt advantage for the RD approach. Despite this, there was a trend toward less instances of high bubble grade in the divers using the GF approach, and inflammatory markers were more elevated in the divers using RD.

Blatteau study:
Showed more venous bubbles after a deep stop decompression compared to a traditional gas content model with shallower stops.

Swedish Navy study:
Higher bubble grades in the deeper stop dives.

Ljubkovic study:
Showed almost universally high venous bubble grades after decompression from trimix dives using VPM.

Dr. Neal Pollock’s work:
Found apparent success in decreasing bubble grades by de-emphasizing deep stops, and (in particular), by padding shallow oxygen stops.

Dr. Neal Pollock:

"The impact of deep stops is … actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving.
 
Asked another way, we might inquire how the conclusions reached by Hills and those technical divers are different from the way modern-day decompression tables have come into being." JJ

I stand by what I said:
Hills had a small self selected population with a high level of survivor bias included
There was no metric of decompression stress like doppler measurements
AND they still had a high incidence of DCS

Deep stops were an emotionally attractive idea, they just didnt stand up to subsequent statistical or doppler etc scrutiny
 
https://www.shearwater.com/products/teric/
http://cavediveflorida.com/Rum_House.htm

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