34 dives to 15 feet in 4 hours - symptoms

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I would like to thank everyone who shared their knowledge and thoughts on this thread (and please continue to discuss if you feel like that)!

What I have learned so far (among many other things):
  • I am not the only person who is worried about sawtooth profiles. Sawtooth profiles infer many unknowns. Decompression algorithms have mostly been verified with diving profiles with ~one ascent. Sawtooth profiles with dozens of descents+ascents are uncommon.
  • DCS is not unheard of after diving shallow sawtooth profiles.
  • Sawtooth profiles can cause trouble even in shallow water if the dives are excessively long (-> high nitrogen load) and there are countless ups and downs (like in some caves on Yucatan).
  • Sawtooth profiles with dozens of ascents from 15 feet are common in aquarium diving and do not seem to cause any trouble.
  • Sawtooth profiles may be needed in various types of diving to perform other tasks (other than the already mentioned aquarium diving) such as diving related to fish farming or search and recovery diving, and more.
  • Shunts in the lungs or a PFO can cause AGE, which is bad because filtration of bubbles is reduced and more bubbles remain and also because arteries narrow down into capillaries (unlike in venous side where they grow in size).
  • Reminder to myself: bubble trouble is DCI not DCS. DCI is DCS and/or AGE.
  • This was a good repetition of elementary hyperbaric physics and medicine for divers - at least I felt it was.
  • Decompression stress affects our bodies every time we decompress (meaning physical decompression, not decompression stops) given that there is enough dissolved gas to have an impact. This stress may cause damage unseen and undetected and that damage may accumulate over decades: See the Bogaerts case and the interview with him. Thus: better to dive gently and in moderation.
  • I will adopt the following precautions for my future search and recovery dives:
    • Higher FO2. Using nitrox 40 for the sake of simplicity. Pure O2 would bring other issues. O2 makes bubbles too, but it is better than N2. Reduction in nitrogen (from 79% to about 59%) is 20% of gas but 25% of original nitrogen amount. Hope it helps a little.
    • I will be trying to limit the number of ascents. I need to find a way to bring all ropes to the working area at once without getting entangled in a veritable spaghetti. This is not a topic to be discussed in detail on this physiology/medicine forum.
    • I will limit my gas amount to 2400 litres. Bigger tanks would allow more dives. The idea to carry bigger tanks has now been adandoned. More diving days. Less harm. More money.
    • I will incorporate short non-mandatory decompression stops somewhere halfway to the surface to control my ascent rate. I will do this once darkness recedes and is replaced by red light (note: decompression means pressure reduction means ascent; decompression stop means constant depth; mandatory decompression stop means a physiological need to stop and this is frequently shortened as "deco dive"). I have no idea if stopping helps but surely it does not do any damage. Can't be bad to take 30 secs to evict a bubble or two :D And I get the warnings off my divelog.
 
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that's eff'n hilarious
True, it is Mark Powell.

Colin discussed two bubbles.
Mark discussed many bubbles.
Don't know which one case is more harmfull.

Sorry for my digression into politics :D Continued talk at the pub.
 

John C. Ratliff

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I'm curious, was the op-ed diving not only in shallow water, but at altitude? That could also influence the potential for DCI.

SeaRat
 
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Maybe we'll see some interesting data on repeated ascent dives as more people use that new O'Dive gadget. I "believe" that repeatedly yo-yo-ing from 25 feet is more likely to mildly bend you than staying at 25 feet for several hours (even until saturated) and ascending once. I don't know why this would be. If I were going to throw some wild speculation up on the internet perhaps expanding then crushing "silent" bubbles allows them to migrate into places they normally wouldn't. Or perhaps the deco algorithms aren't modeling the behavior of fast tissues with total accuracy. Our models are just that, models, not precision measurements of what is really happening physiologically. We KNOW they're not always correct.

As others have said, the scientific data is missing, but there appears to be a large enough body of anecdotal evidence to consider shallow dives with repeated ascents a hazard that should be mitigated with precautions as we do for deep dives. Minimize ascents, use nitrox, ascend REALLY slowly, stay warm during the dive, stay very hydrated, don't overwarm yourself or exercise hard immediately following the dive. Even if taking these measures seems silly for 30ft dives.

Being cold is a big predisposition to DCS hits, you've mentioned being cold a few times. Up your thermal protection. We do a lot of cold dives here and I try to make a point of planning those more conservatively. One way to minimize ascents on working dives is to stay on the bottom and use an SMB to signal when you want your surface support to lower a mooring chain or do whatever you need them to do.

As for the argument over the statement "all dives are deco dives" - I like the adage. Of course "deco dive" does have a specific meaning as it relates to mandatory ceilings. But it's important to remind ourselves that we absorb and offgas nitrogen on EVERY dive and we shouldn't be cavalier about rapid ascents even on recreational profiles.
You give some really good advice indeed!

Being cold at the end of the dive is a problem because peripheral blood flow is restricted (e.g. the skin, toes, fingers). If those body parts warm up too fast then you may have a problem. It is not bad to feel cold in the beginning. It would mean less ingassing. Turn the heating slowly on towards the end of the dive.

Using an SMB to signal things is a great advice! Thanks!!!

It is noteworthy that
  1. on the first day I was breathing air, did 34 ascents, not feeling cold, and I felt exceptionally exhausted afterwards.
  2. next time I was breathing nitrox 40, did 30 ascents, feeling cold at the end (shivers), and I felt a little bit better.
Hence, cold stress does not fully explain this fatigue. I felt colder but I felt better afterwards. It has more to do with minor changes in gas and ascents, and possibly with some random factors (like getting used to the ordeal). This is not a scientific experiment so everything is a bit uncertain.

If my computer says "happy happy joy joy" and yet I feel **** after the dive, then something is wrong, and needs to be corrected.

All dives are deco dives:
(I will interpret "deco" as "decompression")
This is a physical fact and all people who claim otherwise are simply wrong no matter what they might have done in diving. Decompression means reduction in pressure which in diving means reduction of depth, i.e. ascent. All dives where the diver resurfaces are decompression dives. If a diver dives, perishes, and forever remains on the bottom, then it is a compression dive only. Decompression stops refer to those moments where decompression (ascent) stops. This means constant depth. A mandatory decompression stop is required either to avoid the risk of the bends or because you spouse says so. Dives with mandatory decompression stops are commonly referenced as "deco dives".
 
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I'm curious, was the op-ed diving not only in shallow water, but at altitude? That could also influence the potential for DCI.

SeaRat
It was at sea level. Cold and physical though. Cold stress is a factor but I've done this twice and the introduction of 40% nitrox and experience and some slower ascents and the removal of 10% of dives made me feel slightly better,
 

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True, it is Mark Powell.

Colin discussed two bubbles.
Mark discussed many bubbles.
Don't know which one case is more harmfull.

Sorry for my digression into politics :D Continued talk at the pub.
:D:D
 

Dr Simon Mitchell

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We just had a long and very informative thread on this a few months ago. Like this one, it started with a lot of "I heard that..." and "I once read about a study that..." comments. About halfway through it had some real information.

Here is the thread: Is DCS possible under 20fsw, or 100% impossible?

Here is one of the studies mentioned: Bubble formation and decompression sickness on direct ascent from shallow air saturation diving - PubMed

The gist is that you don't get bent shallower than 20 feet.
Hello John,

There is another paper (van Liew 2005) that supports the concept the DCS is extremely unlikely in depths 20' or less, but based on a larger dataset than the one you cite. Once again, it is based on the results of shallow saturation dives by humans, so fairly convincing. I have attached it. My apologies if you already know about this from the other thread. I did not go through the whole thing to see if the van Liew paper came up.

Also, to all, there has been some confusing commentary about the terms DCI, DCS and AGE here. It is correct that decompression illness (DCI) is a collective term for decompression sickness (DCS) and arterial gas embolism (AGE). 'DCS' refers to the consequences of bubble formation from dissolved gas (usually nitrogen). Such bubbles can form in blood as it passes through supersaturated tissues, and will appear in the veins. These bubbles are very small. While it is technically correct that venous nitrogen bubbles that cross a right to left shunt become 'arterial gas emboli', the consequences known to be associated with this process, such as spinal, cutaneous (skin) and inner ear symptoms, are still called 'DCS' (e.g., spinal DCS or inner ear DCS), not AGE. The diagnosis of 'AGE' is generally reserved for dramatic very short latency stroke-like symptoms thought likely caused by very large bubbles introduced to the arterial circulation by pulmonary barotrauma. The tiny venous nitrogen bubbles that cross a PFO are very unlikely to produce such symptoms. All of this is described in an editorial I recently wrote, which I have attached.

Simon M
 

Attachments

  • van Liew and Flynn DCS saturation depth threshold.pdf
    2.3 MB · Views: 8
  • Mitchell_DCSorDCI_Editorial.pdf
    2.7 MB · Views: 10
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