Deep stops and ascents...

[H2Andy]

yeah, just thinking outloud

something like "friction" between the exiting nitrogen and the cells which translates
into energy being spent to repair or soothe the cells

no basis for it whatsoever other than a thought

 

[Cacia]

Lamont, since I have forced myself to spend more time on ascent (only hard on wrecks, cause you try and get more time on/in it), I have stopped crashing after diving. The reason I relate this to diving is that it seems similar to what I notice when I compare air to nitrox dives. I used to nap for two hours after two air dives. usually 100+ and then a long 50 +- min shallow.

 

[DivesWithTurtles]

From this DAN publication (worthwhile reading):

"In spite of gradual reductions in bottom time over the past decades, ascent rate and the addition of an arbitrary shallow safety stop at 5 m (15 ft) for 3-5 minutes, neurological decompression sickness remains a significant problem in recreational diving. A primary target for DCS appears to be the spinal cord with its 12.5 min half-time. This research with human divers produced two primary findings: (1) Slow ascents (3m/min) produced greater bubble grades than faster ascents (see Figure 5); and (2) the inclusion of a deep stop together with a shallow stop yielded the lowest bubble grades (see Figure 6). Therefore, contrary to popular belief, this study has indicated that a slow, linear ascent may produce significantly more bubbles than a more rapid ascent rate with a deep and shallow stop. Further, the optimal method for reducing post-dive bubble production is the combination of an ascent rate of 10 m/min (30 fsw/min) with a deep stop at about half the depth of the dive and a stop at 15 fsw (5 m) for 3-5 minutes."

(Emphasis added by me.)

 

[Fastmarc]

hmm.... very similar to what I read on that rgbm mares site.

 

[DandyDon]

No, Dandy Don. Oxygen is almost completely transported on hemoglobin molecules in the blood. Nitrogen does not compete for those binding sites. Having excess dissolved nitrogen (or bubbles) does not mean reduced oxygen availability to tissues.

Thanks Doc - I stand corrected. So we don't know why N2 loading causes fatigue really...??

It is good to see that half here are doing deep stops. Wish good ol' Padi would come to the 21st Century on their teachings here.

 

[lamont]

So the question remains - what is causing this fatigue? The hypothesis of deep stop proponents is this is actually a sign of sub-clinical DCS. In other words, we are hurting ourselves with straight ascents, just not badly enough enough to require medical attention.

One theory is that the N2 bubbles affect red blood cells in a way that causes a temporary DIY sickle cell anemia effect (the RBCs wind up blocking bloodflow through capillaries).

 

[DandyDon]

How about "Too many N2 molecules get where they don't belong and disrupt your body's abilities..." It's be nice to know the details, but if they're not really available?

 

[vkalia]

I think there are a couple of scenarios one might consider before making a blanket statement. For one thing, YOU, as an observer of ME doing a deep stop (half max depth for 1.5-2 minutes) at 24 m/ 78 fsw, have no idea what is behind my rationale. Thus snickering seems a bit uncalled for.

To be honest, unless you were diving with me as a buddy, I'd have no idea what you were doing on your dive nor would I care... I dive to enjoy myself, not to evaluate others. So sorry if I gave the impression that I'd laugh at you for doing whatever it is you were doing. Your dive, your plan, your decision - I dont fit into the picture at all.

And I don't believe that a deep stop after a depth of 78 feet would be of no benefit. I think it's actually a safe practice. The ata pressure difference between 78 fsw and 80 fsw is really pretty minimal. It slows ascents overall, gives a diver confidence and experience while hanging in blue water, and does give them an extra couple of minutes to off-gas.

More power to you.

I cannot argue with theory and DAN studies, especially when they use fuzzy terms like "may increase bubble formation" or "have noticed the possibility of increase in bubble formation" (emphasis on "may" and "possible"). I can only speak for mysellf and my experiences.

I do, on average, 4 dives in the 30-40m range every week. When I learned about deep stops, I decided to try it out for myself. I spent about 300-something dives seeing what would happen with and without deep stops. For typical no-stop diving (2 dives/day, 1 deep, 1 shallow), it made no difference to me in terms of fatigue, "feeling cleaner", etc.

So yes, it may indeed be safer, so by all means do it if you want to. However, in *my* experience, it doesnt provide *me* with any material benefit for no-stop diving.

Re. post-dive fatigue - IMO, diving is not nearly as effortless as we think it is. We are swimming against a lot of drag and in a fairly high pressure environment. Plus, we do suffer heat loss, even in the warmest of waters. I find that if I am going swimming after a while, I tend to be very exhausted afterwards; however, after a week or so of regular swimming, I tend to feel better. Ditto diving - at the start of every season, it takes me a few weeks to adjust to diving daily. I feel knackered even after I have spent 4-5 hours doing CW... and I think we can all agree that CW is not getting me bent! After a while, I feel a lot less tired.

So IMO, these factors may be more responsible for the typical post-dive fatigue than sub-clinical DCS.

Happy diving,
Vandit

 

[vkalia]

Addendum, as I realize that I appear to be exceedingly "anti-change" even by my own cynical standards:

I do buy the concept of deep stops in general. A conscious decision to reduce bubble buildup has saved me from getting bent on atleast 2 occasions, the last being 2 months ago when I had to do 2 flying ascents from 30m to the 5m to pull down 2 "advanced" divers that decided to float up right in the middle of the shipping lane.

Turtle, thanks for that article link. Interesting read, and a very good experiment carried out by the authors.

The first thing that jumps out at me is that they have not equalized "stop time" across the two most relevant cases (case 4/4R and 6/6R) - so in one case you have a diver leaving the water after spending 10 minutes in stops (15/5 and 6/5) and in the other case you have a diver leaving the water after 5 minutes in stops (5/5). The ascent time correlation analysis does not, IMO, address that difference. To me, that introduces a third and very significant variable element.

So probably more research with a more rigorously thought out set of test cases might be in order. I'd also be interested in reading the results of the peer review provided upon publication of this article, as I do not have the expertise to comment on the mathematical and testing techniques used.

Second, profiles of 25/25 put you right around the NDLs anyway, and gets you into a range of N2 loading where you are going to have tissue supersaturation on ascent - exactly the sort of scenario where deep stops do make a lot of sense. No arguments there.

Third, at the risk of being curmgeonly again, the remaining equation is - what is the relationship between level of bubble build-up and symptoms? The theoretical ramifications are pretty clear, but the impact on practical diving is still unclear, in terms of incremental reduction in possibility of neurological DCS... after all, we are still talking about asymptomatic bubbles.

Looks like there is a fair bit of research that still needs to be done here. Am going to contact DAN/SEAP tomorrow and see what's new in this field.

Vandit

 

[lamont]

I do, on average, 4 dives in the 30-40m range every week.

I usually do 2/wk, ~100/yr, and the bulk of them are in that range, and generally up against the NDLs for the gas that I'm diving (and occasionally now creeping over it...)

Ditto diving - at the start of every season, it takes me a few weeks to adjust to diving daily.

"dive season"?

Seriously, I know what my body feels like after diving, and I know on some occasions that I've had very far outliers in terms of fatigue and post-dive napping. Those were dives without deep stops and/or on air. I've also got tons of dives where I've gotten cold and that's a different (and more normal) feeling of fatigue.