Kevrumbo
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Unfortunately, these bubble model tenets of Jarrod Jablonski, George Irvine and Andrew Georgitsis as it applies to DeepStops in Ratio Deco have not been supported by emerging studies (i.e. NEDU "DeepStops" Study: Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dive).
Quoting Jarrod Jablonski in the linked article below:
". . .The earliest technical diving uses of deep stops were based almost solely upon personal experience. Several individuals, many within our group, toyed excessively with various ranges of deep stops, employing progressively deeper stops for varying times and then shortening the times in the pursuit of maximum efficiency. George Irvine and I pushed these and other assumptions to their limits, consistently striving to develop a means of maximizing decompression efficiency; George has been especially aggressive in this regard, helping to establish a true minimum range for decompression times. Divers from the WKPP established several working rules of thumb for deep stops, such as the convention of a first stop that should start one atmosphere shallower than one's maximum depth during the dive . . . Here, deep stops are specifically defined by the point in which ambient pressure and leading compartment pressure (theoretical pressure within body tissues) are equal. Deeper than this point would actually result in on-gassing, while too shallow could promote bubble formation. . ."
See also Decompression Experimentation | Global Underwater Explorers
(Similarly, compare below the heatmap of GF 10/82 versus GF 66/66):
Even the gas kinetics assumption (vis-á-vis Helium being a faster inert gas than Nitrogen, thus requiring DeepStops to prevent early leading compartment fast tissue supersaturation & potential bubbling), is being challenged. Everything is coming back to efficient margined GF application of Bühlmann's dissolved gas content model. . .
Quoting @Dr Simon Mitchell :
". . .This brings us to the fact that we have seen the recent emergence of data that suggest the deep stop approach might not be the best one. In particular, these data suggest that the logic of protecting fast tissues from supersaturation early in the ascent at the expense of increased supersaturation in slow tissues later in the ascent may be flawed. Whether one likes the relevant studies or not, they are all we have at the present time to illuminate this issue.
So, was the bubble model fashion a bad idea, and where does this leave the majority who have been using some degree of "deep stopping" with apparently good outcomes? Do we abandon deep stops entirely eg go to 90/90 as you hypothesised, do nothing, or do something in between?
I guess the first thing to acknowledge is that the studies indicating a disadvantage for deep stops are not the diving equivalent of multiple large multicentre randomized trials all showing that the risks of a widely used drug are greater than its benefits. On the basis of that sort of data you would probably stop using the drug overnight. The diving world data concerning deep stops are not as definitive as that. As more data emerge the situation may become clearer (or more blurred)! So, at the present time, as an informed commentator, I would not go so far as to recommend that the entire world dives 90/90 or 80/80 from tomorrow onward even though I personally would not be surprised if the outcomes were as good as (or better than) what we are getting now (if we were able to measure them!). Partly, this hesitancy to advocate substantial wholesale change arises from the certainty that every diver who subsequently got bent would inevitably blame it on the change in their decompression practice! The deep stop trend evolved over a substantial period, and if the data continue to be supportive, it may have to "de-evolve" over a substantial period.
Equally, I do believe the data are strong enough (and bear in mind they are the only data) to consider a change in practice if you are a strong "emphasizer" of deep stops. In practical terms, "de-emphasizing" deep stops (or lessening any potential disadvantage) would mean using bubble models on very high conservatism settings, and with gradient factors, avoiding very low GF-lo values. I have been evolving my own use of GFs and am currently around 50/80 . . .sometimes as low as 70 for the high value when we are at places like Bikini and I am the only diving physician. Pre-NEDU study I was GF lo of 20. This is my personal perception of a sensible graduated response to the way the evidence is currently evolving. I may well go further in future (guided by the evidence).
Sorry about the long post. Hope it makes sense."
Simon M
Deep stops debate (split from ascent rate thread) - Page 13
Quoting Jarrod Jablonski in the linked article below:
". . .The earliest technical diving uses of deep stops were based almost solely upon personal experience. Several individuals, many within our group, toyed excessively with various ranges of deep stops, employing progressively deeper stops for varying times and then shortening the times in the pursuit of maximum efficiency. George Irvine and I pushed these and other assumptions to their limits, consistently striving to develop a means of maximizing decompression efficiency; George has been especially aggressive in this regard, helping to establish a true minimum range for decompression times. Divers from the WKPP established several working rules of thumb for deep stops, such as the convention of a first stop that should start one atmosphere shallower than one's maximum depth during the dive . . . Here, deep stops are specifically defined by the point in which ambient pressure and leading compartment pressure (theoretical pressure within body tissues) are equal. Deeper than this point would actually result in on-gassing, while too shallow could promote bubble formation. . ."
See also Decompression Experimentation | Global Underwater Explorers
And tying all together now, the 20/80 and 70/70 GF's may have similar total deco stop times and profile shapes above, but @UWSojourner 's heat maps tell the true damning story showing the pattern of latent slow tissue on-gassing, supersaturation and surfacing decompression stress.
(Similarly, compare below the heatmap of GF 10/82 versus GF 66/66):
Even the gas kinetics assumption (vis-á-vis Helium being a faster inert gas than Nitrogen, thus requiring DeepStops to prevent early leading compartment fast tissue supersaturation & potential bubbling), is being challenged. Everything is coming back to efficient margined GF application of Bühlmann's dissolved gas content model. . .
Quoting @Dr Simon Mitchell :
". . .This brings us to the fact that we have seen the recent emergence of data that suggest the deep stop approach might not be the best one. In particular, these data suggest that the logic of protecting fast tissues from supersaturation early in the ascent at the expense of increased supersaturation in slow tissues later in the ascent may be flawed. Whether one likes the relevant studies or not, they are all we have at the present time to illuminate this issue.
So, was the bubble model fashion a bad idea, and where does this leave the majority who have been using some degree of "deep stopping" with apparently good outcomes? Do we abandon deep stops entirely eg go to 90/90 as you hypothesised, do nothing, or do something in between?
I guess the first thing to acknowledge is that the studies indicating a disadvantage for deep stops are not the diving equivalent of multiple large multicentre randomized trials all showing that the risks of a widely used drug are greater than its benefits. On the basis of that sort of data you would probably stop using the drug overnight. The diving world data concerning deep stops are not as definitive as that. As more data emerge the situation may become clearer (or more blurred)! So, at the present time, as an informed commentator, I would not go so far as to recommend that the entire world dives 90/90 or 80/80 from tomorrow onward even though I personally would not be surprised if the outcomes were as good as (or better than) what we are getting now (if we were able to measure them!). Partly, this hesitancy to advocate substantial wholesale change arises from the certainty that every diver who subsequently got bent would inevitably blame it on the change in their decompression practice! The deep stop trend evolved over a substantial period, and if the data continue to be supportive, it may have to "de-evolve" over a substantial period.
Equally, I do believe the data are strong enough (and bear in mind they are the only data) to consider a change in practice if you are a strong "emphasizer" of deep stops. In practical terms, "de-emphasizing" deep stops (or lessening any potential disadvantage) would mean using bubble models on very high conservatism settings, and with gradient factors, avoiding very low GF-lo values. I have been evolving my own use of GFs and am currently around 50/80 . . .sometimes as low as 70 for the high value when we are at places like Bikini and I am the only diving physician. Pre-NEDU study I was GF lo of 20. This is my personal perception of a sensible graduated response to the way the evidence is currently evolving. I may well go further in future (guided by the evidence).
Sorry about the long post. Hope it makes sense."
Simon M
Deep stops debate (split from ascent rate thread) - Page 13
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