Deep Stops?

[RumBum]

What is current research showing about the efficiency of deep stops? After a deep (100 ft or so) dive where you are on the edge of NDL's, is it beneficial to do a deep stop, i.e. 50' for 2 minutes or are you just continuing to add to your body's nitrogen loading? This is regarding dives within no decompression limits with a normal safety stop of 3 min at 15.

 

[Dr Deco]

Hello Readers:

Sorry about the lateness of this reply. I was ill for several days.

Deep Stops Theory

The theory of the deep stop is that it prevents micronuclei from expanding during an ascent, in accordance with Boyle's Law. When the nuclei are small, the internal, Laplace pressure generated by surface tension remains high. This, in turn, maintains a high pressure inside the nuclei and the driving gradient is for the free-gas phase to move from the microbubble into the liquid portion of the tissue. Migration by diffusion then allows the dissolved nitrogen to be carried away by the circulation.

That is the theory, anyway.

Putting deep stops into practice requires knowledge of the size of the microbubbles. Since these come in a variety of diameters, it also requires a knowledge of the size-number distribution. None of this is really known and it probably varies quite a bit from diver to diver.

Dive Studies

Only one study to date has been clear about that concept [reference below]. This was a crossover study that increased the statistical power of the study. It is not a particularly deep dive as recreational diving goes. It did show a clear reduction in Doppler-detectable gas bubbles with the deep stop.

In the recent class on Deep Stops at the Annual UHMS meeting, there was a lot of "evidence" along the lines of "well, it works." Things can work though not for the reason given. I suspect that this will be a difficult issue to sort out.

Dr Deco :doctor:


References :read:

Marroni A, Bennett PB, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Balestra C. A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. Undersea Hyperb Med 2004; 31(2):233-243.

 

[Diver0001]

What is current research showing about the efficiency of deep stops? After a deep (100 ft or so) dive where you are on the edge of NDL's, is it beneficial to do a deep stop, i.e. 50' for 2 minutes or are you just continuing to add to your body's nitrogen loading? This is regarding dives within no decompression limits with a normal safety stop of 3 min at 15.

In terms of diving protocol there are two things to be said about this. First is

1) So what? Nitrogen loading isn't bad but ascending too fast is. It's proper offgassing that matters..... If you have the air and it adds two minutes to your bottom time and you can take it in terms of your NDL then you're not having an issue.

2) ...and I think this is what you were asking.... YES there is a minimum ascent rate at which you should start adding the ascent time to your bottom time. As far as I can reason given the models we have, if you're not ascending at more than 3 metres per min then you have to add your ascent time to the bottom time. If you're ascending between 3 and 10 metres per minute then you're in the zone that most deco models seem to "like". If you're over 10 and under 18 then you're in the zone that most models liked until the late 80's and if you're over 18 you should stop and hang until "your clock catches up to your depth" if you get my meaning.

Dr. Powell, care to comment on that advice?

Also, if you could, I hear some doubt (if I'm reading your right) in your acceptance of bubble theory that wasn't there 18 months ago when I was on scubaboard a lot. Would you care to comment about if you feel there is something about the bubble theory that you think needs more research and/or what divers should think about the current "best guess" theory....

I know that's a tall order but I also know you're up to the task of showing us where "cut and dry" ends and the "grey area" begins.

Finally, I'm glad you're feeling better. I hope your illness wasn't serious.

Cheers,
R..

 

[DA Aquamaster]

I can only give you a case study of one as "evidence" and it is evidence of the the "well it works" variety.

I used to live in an area that allowed me to spend weekends on my boat and dive a lot. It was comon to show up on Friday afternoon do an afternoon and evening dive, put in 4 dives on Satruday and 4 more on Sunday, all in the 60-150 ft range with most pushing the NDL, and on occassion some intentional deco on the deeper dives (using 50% for a deco gas), but in all cases extending the safety stop until the bar graph was in the green, rather than yellow.

I never bent my computer, and stayed within it's recommended ascent rates (60 fpm below 60 feet and 30 fpm above 60' with a 3 minute safety stop at 20', and as indicated above extended safety stops to put me at the top of the green rather than yellow when getting out.

Usually on Monday morning I felt very fatigued and sometimes even flu like even on weekends where the NDL's were not exceeded and no intentional decopmpression dives were done.

When the pattern dawned on me and I realized there was more here than being tired, I changed how I dove. I made the same number of dives to the same depths for the same times, but I started doing deep stops (2 minutes at 1/2 max depth,) and slowed my ascent to no more than 30 fpm and added 1 minutes stop every 10' from the deep stop to the surface with the same 3 minute stop at 20' to keep the computer happy. I felt great on Monday mornings with none of the same subclinical symptoms.

On my deco dives I changed to computer generated tables using a bubble gradient model that left me making much deeper stops for shorter periods of time and this again left me feeling great the following day.

Now, it may have been the deepstop or the slower ascent from 1/2 max depth imposed by the 1 minute stops every 10', or more likely a combination of the two, but regardless of 'why' it worked much better.

 

[Ken abucs]

Here's a nice article from DAN on the topic.

DAN Divers Alert Network

 

[BlueDevil]

How well regarded is the Marroni study in scientific/medical circles? eg. were the numbers of divers adequate, was the design of the study and the statistical methods used valid, how did they precisely control ascent rates etc.

The study certainly does seem to show a benefit of deep stops and I guess that's a result we all like to see since it is such an easy thing to include a deep stop or two. However paradoxically the slowest ascent rate of 3m/min gives a greater bubble score than an ascent rate of 10m/min, or even 18m/min!! How do we explain this in light of the general belief that slower ascents are better?

 

[Gene_Hobbs]

How well regarded is the Marroni study in scientific/medical circles?

When looking at the 2004 UHM paper...

Bennett PB, Marroni A, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Leonardi MG, Balestra C. A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. Undersea Hyperb Med. 2004 Summer;31(2):233-43. 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

Then there is the 2007 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: 7901
NOTE: There is a table error correction that we can not add as it was published in 2008 and our embargo on this journal does not allow us to add it yet.

 

[Bismark]

I can only give you a case study of one as "evidence" and it is evidence of the the "well it works" variety.

I used to live in an area that allowed me to spend weekends on my boat and dive a lot. It was comon to show up on Friday afternoon do an afternoon and evening dive, put in 4 dives on Satruday and 4 more on Sunday, all in the 60-150 ft range with most pushing the NDL, and on occassion some intentional deco on the deeper dives (using 50% for a deco gas), but in all cases extending the safety stop until the bar graph was in the green, rather than yellow.

I never bent my computer, and stayed within it's recommended ascent rates (60 fpm below 60 feet and 30 fpm above 60' with a 3 minute safety stop at 20', and as indicated above extended safety stops to put me at the top of the green rather than yellow when getting out.

Usually on Monday morning I felt very fatigued and sometimes even flu like even on weekends where the NDL's were not exceeded and no intentional decopmpression dives were done.

When the pattern dawned on me and I realized there was more here than being tired, I changed how I dove. I made the same number of dives to the same depths for the same times, but I started doing deep stops (2 minutes at 1/2 max depth,) and slowed my ascent to no more than 30 fpm and added 1 minutes stop every 10' from the deep stop to the surface with the same 3 minute stop at 20' to keep the computer happy. I felt great on Monday mornings with none of the same subclinical symptoms.

On my deco dives I changed to computer generated tables using a bubble gradient model that left me making much deeper stops for shorter periods of time and this again left me feeling great the following day.

Now, it may have been the deepstop or the slower ascent from 1/2 max depth imposed by the 1 minute stops every 10', or more likely a combination of the two, but regardless of 'why' it worked much better.

I found pretty much the same thing in regards tot he recreational diving part (130-up) I did two back to back live aboard trips to the same location, doing the same dives and the second trip I included deep stops (50% of depth) and a slower ascent rate with 1 min for each 10' (30 second holds, 30 second slides). The first trip I had a continuous headache for the trip and flu like symptoms that I thought was caused by dehydration despite maintaining a high level of fluid intake and The second trip I had nary a problem. Call it anecdotal evidence if you like, but it works for me......... Haven't had any subclinical symptoms in the last few years.

 

[BlueDevil]

Thanks Gene, the critique letter and the author's reply are both interesting, but it does leave you wondering where the truth lies.

The theory of deep stops is very appealing and many people (myself included) have obviously adopted the practice since Richard Pyles's interesting article became available on the net many years ago. There is certainly a lot of anecdotal evidence, such as that provided by posters on this very thread. And lots of theory from the developers of bubble models etc. However none of that constitutes 'proof' from a scientific perspective, and one could always argue the placebo effect could be responsible for the reported subjecyive 'improvements' experienced when deep stops are incorporated.

I would have to say I find the theory and anecdotal evidence fairly compelling but I would really love someone to come out with a definitive study that conclusively proves the issue one way or the other. I guess quality research in this area is going to be difficult, costly and time consuming, (and you would have to demonstrate it across a range of differing depths and times) but I hope eventually it gets done . It would sure be nice to be able to say conclusively "deep stops do work" rather than having to qualify your statement by saying "deep stops probably work"

 

[Rhone Man]

I would have to say I find the theory and anecdotal evidence fairly compelling but I would really love someone to come out with a definitive study that conclusively proves the issue one way or the other.

Agree, but you could say that about just about everything relating to decompression theory though...