Blow a Safety Stop? Redescend ?

[Bubbletrubble]

I have no idea as to going back down if you blew your stop. Would I do it? Yes, I would, with the simple understanding that if those bubbles were still there, then the increased pressure would help drive them back into solution in the bloodstream, rather than the bubbles being transported to an area of the body where they could do harm. Again, they would be off-gassed through normal respiration (with varying times, depending on a lot of factors, below). Please understand the physics of what is happening with the air bubbles, and that going back down to a safety stop depth does nothing detrimental - at all. If you have ever watched your computer during this time (it's interesting to see how they react), they often will increase the amount of time for the recommended stop (I dive Suunto's, and that's what mine tells me).

@dpaustex: I agree with many statements in your last post...but not the quoted paragraph above. Basing your decision to re-descend (under those circumstances, i.e., omitted safety stop) on the physics of bubble growth dynamics is, at best, an aggressive interpretation of the science. It's dangerous to overstate the findings of published scientific work and, even more so, to base our real-world dive profiles on bubble studies alone. Simply put...we do not understand the relationship between intravascular bubbles (as recorded by Doppler studies) and the pathophysiology of DCS. Period.

 

[Thalassamania]

Woah, folks!!!! Too many bad terms being thrown around here.

First, safety stops are recommendations. Second, some people keep calling these a "deco -stop"...quit doing that!!! If you are doing recreational diving, your are NOT doing "deco" diving. Wrong forum, wrong place. All of the charts being referenced are for "no decompression diving", which is staying within those chart limits. Again, NOT DECO!!!!

Okay, so what "should" you do? First, understand the purpose of the safety stop. Anyone remember what was taught to them in their OWD course? The safety stop is an "added safety measure of 3 to 5 minutes at 10 to 30 feet that divers should take after no-decompression dives to help reduce silent bubbles and the risk of pressure related injuries." (reference SSI manual).

Okay, first understand that the safety stop is a recommendation. Does it mean you won't get bent? No. There are too many factors involving DCS. The whole purpose of the recommended safety stop is to let the blood circulate throughout your entire body, which will help get rid of the very tiny bubbles that may (or may not) still be present in portions of your body. The idea of 3 to 5 minutes was to allow these bubbles more "contact" time with the blood to go back into solution, which will then be off-gassed through the normal respiratory cycle.

I have no idea as to going back down if you blew your stop. Would I do it? Yes, I would, with the simple understanding that if those bubbles were still there, then the increased pressure would help drive them back into solution in the bloodstream, rather than the bubbles being transported to an area of the body where they could do harm. Again, they would be off-gassed through normal respiration (with varying times, depending on a lot of factors, below). Please understand the physics of what is happening with the air bubbles, and that going back down to a safety stop depth does nothing detrimental - at all. If you have ever watched your computer during this time (it's interesting to see how they react), they often will increase the amount of time for the recommended stop (I dive Suunto's, and that's what mine tells me).

But to say that if your computer didn't "tell you" anything was wrong is a misunderstanding of the gas laws, and how the lack of a safety stop could (note the would "could") impact you. There are so many variables involved (how much residual nitrogen you have, how many repetive dives have you already done, how hydrated you are, dive depth, etc.), that it isn't something to trifle with. Computers, for the most part, have conservative dive profiles. But computers are no guarantee how an individual's own physiology will specifically impact them. Again, the safety stop is only a recommendation, not a requirement.

I have done wall dives, where we came back up so gradually (working back and forth along the face), that the safety stop was "built in" to the dive, and while the computer "triggered" the safety stop when I hit 20 feet, I just kept on swimming.

Safety stops were invented as a way to slow the overall rate of ascent, nothing more and nothing less. It was MUCH LATER found that safety stops also reduce Doppler detectable bubbles ... what that actually means is unknown, but some have prematurely jumped on the bandwagon making the claim that safety stops reduce the risk of DCS even if you have made a slow ascent.

Not to be the contrarian, but no. All dives are deco dives. Stops can be deep or shallow, optional or mandatory. All stops are decompression stops as we do them to avoid DCS. A safety stop is a fun way to say "optional deco stop" without giving peeps too many reasons to just skip it.

You're splitting hairs, I have to "decompress" when I climb the 17 steps up to my study.

dpaustex: I agree with many statements in your last post...but not the quoted paragraph above. Basing your decision to re-descend (under those circumstances, i.e., omitted safety stop) on the physics of bubble growth dynamics is, at best, an aggressive interpretation of the science. It's dangerous to overstate the findings of published scientific work and, even more so, to base our real-world dive profiles on bubble studies alone. Simply put...we do not understand the relationship between intravascular bubbles (as recorded by Doppler studies) and the pathophysiology of DCS. Period.

Quite correct. Where dpaustex goes astray is in saying, "Please understand the physics of what is happening with the air bubbles, and that going back down to a safety stop depth does nothing detrimental - at all. If you have ever watched your computer during this time (it's interesting to see how they react), they often will increase the amount of time for the recommended stop (I dive Suunto's, and that's what mine tells me)." Going back down does do something detrimental, it compresses bubbles and enables them to pass into the arterial circulation where they are in a position to cause damage, this is an effect that no computer is programed to account for.

I'm kinda amazed at how many instructors seem to be unaware of this issue, I guess those of us who are aware of it have done a lousy job of spreading the word. Believe me, no one is immune ... a well know university DSO has a big patch of anesthesia on his left thigh as a direct result of going back down to clear the anchor.

 

[dpaustex]

Hmmm...I am going to defer on some of the comments. I was aggressive in my statements, based on the physics alone. That is all I was trying to say, and I stand by that on the physics. However, I do understand the physiology that some of the "larger" bubbles may be able to pass from one side of the heart to the other. Additionally, if what I understand is correct, further compression occurs in the heart, with a pressure drop once the blood passes through the chamber. Such pressure drops (I don't know the amount, just understand the general theory of pump mechanics) could cause a problem, as such a drop could allow some bubbles to "come out of solution" on the discharge side of the heart. The ability of the "bubbles" to be reintroduced into the blood is a true unknown. The viscosity of the blood is one determinant of which I am aware (I'm not going to quote the chemistry/physics gas law), and I would venture others exist.

Lots of good discussion, and lots of unknowns in the whole mix. I do not know the degree of accuracy the Doppler system can achieve, and whether or not such studies have actually been done IN the water. Would be interesting data, no?

 

[dpaustex]

I want the cardiologists on the post to address the bubble issue. Specifically, if you blew a stop, and were concerned, what are the specific dangers in going back to 15 ft for 5 mins? I understand the "maybes" of the recompression, but it would seem there is an equal downside that if you did get bent, the bubbles that do exist could be traveling somewhere. This could cause heart issues, brain issues, etc. The unknown would be the size/location of the bubbles. I don't know of any studies that have addressed these "what-ifs", but would certainly love to hear if there is something out there I haven't heard.

Bubble size is not "fixed" until you get to the surface. I know that it is possible for bubbles to "merge", as observed in flow tanks in the lab. So, if you have varying size bubbles, it would seem they are already a "risk" if you've come up too fast. The greatest percentage change in pressure occurs in the last atmosphere jump, but I do not know at what differential pressure the bubbling "occurs". Can anyone comment on that?


Thoughts?

 

[Thalassamania]

By defintion, you do not get bent if you fail to make a safey stop!

 

[H2Andy]

Specifically, if you blew a stop, and were concerned, what are the specific dangers in going back to 15 ft for 5 mins?

you mean as opposed to the reverse profile/bounce dive issues?

 

[Doc Harry]

The NOAA diving manual, although not always current or correct, has a lot of great info on this topic.

 

[dpaustex]

Okay, I am getting a bit lost with the parsing in the discussion. The original question was whether or not to go back down.

I guess the question has too many factors. Was it a repetitive dive. How deep and how long were all of the dives?, etc.

But if the treatment is a chamber, the physics of "in water" recompression remain the same (although with shorter time, different gas mixture, etc). As I understand it, the tissues put the nitrogen back into the blood (venous side), it goes through the heart, to the lungs, and respiration off gasses it. Too rapid an ascent rate causes "excess" bubble formation (not my term). These bubbles can (do?) coalesce and can cause issues.

However, the physics don't change. A hyperbaric chamber increases the pressure to force the bubbles back into solution. That, coupled with a richer breathing gas mixture, helps heal the body, and potentially the areas damaged by the bubbles.

Now the interesting issue is if there is a hole in the heart wall, whereby a portion of the venous blood does not go to the lungs, but into the body along with the oxgenated blood. Obviously not a good thing, because then you're dealing with the brain, etc.

I don't remember the specifics, but there was a study done on divers (don't remember whether it was fatalities, or severe DCS), and it was found that the heart hole was an issue in the severity of the problem.

So I ask, what is the difference between in water recompression (I think it would qualify as immediate) than a chamber, in terms of it being harmfull? Again, base it on the physics of both situations, only.

Thanks.

and btw, I don't know who highlighted words in my posts, but I did not add the emphasis on the words, and don't intend it. Not interested in getting flamed, but pointed in the right direction on what current reseach suggests.

 

[vjanelle]

So I ask, what is the difference between in water recompression (I think it would qualify as immediate) than a chamber, in terms of it being harmfull? Again, base it on the physics of both situations, only.

Length(hours), "depth"(some tables take you down to 160'), time(many hours), medical technicians, IV drugs, fluids, and the ability to create eanx mixes for you to decompress off of on demand. Combined with a person that might be already experiencing enough problems that they can't coordinate themselves enough to hold a stop for that time, and you might not be able to create enough high oxygen mixes on demand.

IWR does happen, but it's a dirty little secret that no one wants to take liability for promoting.

 

[Papa_Bear]

here is how I see it, if you had a portable chamber on the way to your location or it was a short requirement less than an hour or so it might be a stop gap measure, so many factors say it is risky. Hypothermia, possible embolism, panic, and a host of other potential problems, including dehydration. With the right diver it is still a maybe. If the required stop (Not a Safety stop) has a big demand you will have to bite the bullet and head for a chamber!

So what answer are you looking for? Do you want your theory reinforced? In most cases the Captain of the ship will make the decision and your input will not matter! That is the real world.........