Extend Deep Stops?

[Soggy_Diver]

Hi,

I just read this article that suggests extending deep stops from 1 minute to 2.5 minutes. The profiles that they describe are similar to some dives that I do, but I am usually diving in colder water (about 50F). I was thinking about whether to extend my deep stops based on this, and I would be interested in your thoughts on that. Do you think this would be worthwhile? Do you see any downside to it?

Thanks,
Soggy_Diver.

: Undersea Hyperb Med. 2007 Nov-Dec;34(6):399-406. Links
Erratum in:
Undersea Hyperb Med. 2008 Jan-Feb;35(1):6 p following table of contents.
Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw).
Bennett PB, Marroni A, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Leonardi MG, Balestra C.
Duke University Medical Center, USA.

In our previous research, a deep 5-min stop at 15 msw (50 fsw), in addition to the typical 3-5 min shallow stop, significantly reduced precordial Doppler detectable bubbles (PDDB) and "fast" tissue compartment gas tensions during decompression from a 25 msw (82 fsw) dive; the optimal ascent rate was 10 msw (30 fsw/min). Since publication of these results, several recreational diving agencies have recommended empirical stop times shorter than the 5 min stops that we used, stops of as little as 1 min (deep) and 2 min (shallow). In our present study, we clarified the optimal time for stops by measuring PDDB with several combinations of deep and shallow stop times following single and repetitive open-water dives to 25 msw (82 fsw) for 25 mins and 20 minutes respectively; ascent rate was 10 msw/min (33 fsw). Among 15 profiles, stop time ranged from 1 to 10 min for both the deep stops (15 msw/50 fsw) and the shallow stops (6 msw/20 fsw). Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives. We also evaluated shallow stop times of 5, 4, 3, 2 and 1 min while keeping a fixed time of 2.5 min for the deep stop; increased times up to 10 min at the shallow stop did not further reduce PDDB. While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.

PMID: 18251436 [PubMed - indexed for MEDLINE]

 

[Dr Deco]

Hello Soggy Diver:

I would guess that the results speak for themselves. I do not have any personal knowledge of these deep-stop extensions, as I was with NASA for the past decade. Astronauts do not do stops, and I have not tested this myself.

 

[Gene_Hobbs]

When reading the paper:

Bennett PB, Marroni A, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Leonardi MG, Balestra C. Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw). Undersea Hyperb Med. 2007 Nov-Dec;34(6):399-406. RRR ID: 3804

It is very important to read the "Letter to the Editor" that followed from Drs. Risberg and Brubakk as well as the erratum. 3805

The Deep Stops Workshop is in a few weeks, it will be interesting to see what we come to after putting everyone in the same room.

 

[Saturation]

When reading the paper:

Bennett PB, Marroni A, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Leonardi MG, Balestra C. Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw). Undersea Hyperb Med. 2007 Nov-Dec;34(6):399-406. RRR ID: 3804

It is very important to read the "Letter to the Editor" that followed from Drs. Risberg and Brubakk as well as the erratum. 3805

The Deep Stops Workshop is in a few weeks, it will be interesting to see what we come to after putting everyone in the same room.

Thanks for making these all available one-stop Gene, very helpful.

The Letter to the Editor is most important, and while I concur with Risberg critique methodologically, I believe Bennett's results still have strong meaning in favor of the stops.

However, controversy over deep stop looms with the available scientific data, so this meeting will be important. Please give us your impressions of the meeting when its over.

 

[Soggy_Diver]

Thanks for the comments, and for the links!

There is a lot here to sort through, since I have just started reading articles on decompression research. The link to letter to the editor seems to be for a previous (2005) article rather than the 2007 article, but some points seem to apply to the 2007 article too, e.g., how to treat bubble scores statistically.

One issue from the letter to the editor that the more recent article seems to take into account is total decompression time. In the 2007 article, Figure 2 shows different profiles, and the total time they require as well as the BSI score. It seems to show that compared to some other profiles that require similar decompression time, the 2.5 minute deep stop results in a lower BSI score.

I will look forward to reading more about this.

 

[lamont]

So, profile 5 in the paper with 3m/min ascent and 5 min @ 6m is actually one of the worst in the doppler results. Profile 6 is the 10m/min ascent with 5 min @ 15m and 5 min @ 6m which is the best one.

But, running zhl16b on both of those profiles, profile 5 seems better in just about every single way. It keeps the oversaturation in the fast compartments lower, keeps the oversaturation on surfacing lower, etc.

The profiles are also similar in terms of overall deco time. The difference is just that instead of doing a constant ascent to the safety stop, the ascent rate is faster and is interrupted by a stop.

And the difference doesn't really seem to be due to increased ongassing during the deeper portion of the ascent in profile 5.

It seems to be arguing for pushing the oversaturation gradient and then holding the depth constant and cleaning up.

 

[lamont]

Basically, I don't understand the point the authors are trying to make about the 12.5 minute compartment... That doesn't seem to have any relevance in the differences between profile 5 and profile 6.

 

[lamont]

hmmm... gene posted the wrong link, i've been talking about the 2005 paper, not the 2007 one.

 

[Gene_Hobbs]

hmmm... gene posted the wrong link, i've been talking about the 2005 paper, not the 2007 one.

Oops! Sorry about that, I can't add the 2007 paper until November... (One year embargo for the UHMS members.)

 

[lamont]

Oops! Sorry about that, I can't add the 2007 paper until November... (One year embargo for the UHMS members.)

Can anyone become a UHMS associate (non-voting) member, or is it limited to some kind of professional relationship to diving? (e.g. they mention scuba instructors explicitly).