Why deeper in the morning?

[GAP-Software]

Thanks for this post. Question about the above. Do you mean the crushing results in a reduction of numbers or a reduction in size.

R..

Mostly a reduction in size.

 

[Diver0001]

Mostly a reduction in size.

Well well. Another fine addition to the board. Welcome Kees.

R..

 

[SDAnderson]

Mostly a reduction in size.

Let me second Diver0001 - welcome to the board, Kees.

 

[GAP-Software]

Let me second Diver0001 - welcome to the board, Kees.

Thanks, All.

I hope, I will have more time to answer questions on this board, than I had in the past.

 

[ScubaDadMiami]

So far, no one answered your question, Wombat. But yes, there IS a physiological reason. "Because your computer tells you so" is not a physiological reason. To put it simply, by doing your deepest dive first, you crush the tiny always-present bubbles in your system that--according to the dual phase bubble model theories--are the root cause of DCS in the first place.

How the hell did they figure that out, you ask? Well, the tiny bubble theory has its roots in empirical data. Some of it came from Hawaiian diving fishermen who seemed to defy the normal tables, sometimes diving to near 300 feet on their first dive, and then blowing a half dozen scuba tanks on progressively shallower dives, all in one day. Later research using gel models confirmed the empirical data by revealing that the bubble nuclei--not just the dissolved gas--play an important role in the development of DCS symptoms. By doing a short, deeper dive first you crush the bubble nuclei and reduce the formation of bubbles from the nuclei "seeds".

There are a lot of hyperbaric research articles on the topic available in various medical and scientific journals, or you could read Bruce Wienke's "RGBM Diving in Depth", for example.

Not to intentionally add confusion, but there are competing theories that hold just the opposite, suggesting to make each dive at least to the same depth or deeper than the previous dives especially during shorter dives. The theory behind this is that there are always some bubbles that occur during the dive. By conducting a shallower dive than the prior dive, this can allow the bubbles to crush just to a point where they can bypass the lungs (which act like filters, trapping the bubbles until they can be offgassed), then traveling to areas of the central nervous system like the brain. When the diver surfaces, the bubbles expand and cause severe decompression illness.

No doubt, there are competing theories out there that come to the exact opposite conculsion of each other. It does leave one wondering what to do.

 

[Dr Deco]

Hello readers:

Nuclei

Shrinkage is generally given as the reason for the physiological effect of deep dives at the beginning of a series. No one has actually ever seen this in living tissue but the concept makes sense as far as the physics is concerned.

In addition, one has the gas loading advantage of deep-to-shallow dives when maximizing the bottom time.

Arterialization

Since divers do not generally encounter neurological DCS following dives that are progressively shallower, I doubt that the passage of bubbles from the venous side to the arterial system [and then the brain] actually occurs. One does not see it in laboratory situations (Doppler monitoring) with animals as the subjects.

Dr Deco :doctor:

 

[ScubaDadMiami]

Hello readers:

Nuclei

Shrinkage is generally given as the reason for the physiological effect of deep dives at the beginning of a series. No one has actually ever seen this in living tissue but the concept makes sense as far as the physics is concerned.

In addition, one has the gas loading advantage of deep-to-shallow dives when maximizing the bottom time.

Arterialization

Since divers do not generally encounter neurological DCS following dives that are progressively shallower, I doubt that the passage of bubbles from the venous side to the arterial system [and then the brain] actually occurs. One does not see it in laboratory situations (Doppler monitoring) with animals as the subjects.

Dr Deco :doctor:

Sorry, Doc. You have it all wrong. Shrinkage, as noted by the famous architect, George Costanza, is what happens when males choose to swim in cold water and then are viewed naked by intended conquests.

All kidding aside, there is at least anecdotal evidence of neurological DCS after conducting short, shallow dives following deeper decompression diving. If this relationship exists, then making progressively deeper dives and taking into account inert gas loading would carry less risk. This seems to make equally good sense.

I can see it both ways. But, just because I believe one way or the other doesn't make it so. It would be great if there were finally some universal agreement on these issues. It would sure take a load off of my mind.

 

[teksimple]

Not to intentionally add confusion, but there are competing theories that hold just the opposite, suggesting to make each dive at least to the same depth or deeper than the previous dives especially during shorter dives.

No doubt, there are competing theories out there that come to the exact opposite conculsion of each other. It does leave one wondering what to do.

All kidding aside, there is at least anecdotal evidence of neurological DCS after conducting short, shallow dives following deeper decompression diving. If this relationship exists, then making progressively deeper dives and taking into account inert gas loading would carry less risk. This seems to make equally good sense.

ScubaDadMiami - I am interested in where you obtained your information for this "competing theory". I have never heard about this, and have read extensively on the subject having been a recompression chamber operator.

As far as the anecdotal evidence you mention, there is also anecdotal evidence that eating hamburgers both before and after diving is involved in hundreds of cases of DCS. Does that mean that there is a link between DCS and the consumption of hamburgers? No, because there are plenty of DCS sufferers who did not eat hamburgers. Repetitive diving increases risk of DCS in general, whether it is deeper or shallower. That is because you are still onloading gas in some areas of your body (known as tissue compartments in DCS models). If the diver and profile you mentioned resulted in DCS, do you also have another diver who did the same dive profile on the first dive but DID NOT dive the second dive? If not, you have no statistical population to make any conjecture--much less indication--as to likelihood of DCS.

Dr. Deco - do you have any info on this "competing" theory?

Thanks!

- Kent

 

[Diver0001]

ScubaDadMiami - I am interested in where you obtained your information for this "competing theory". I have never heard about this, and have read extensively on the subject having been a recompression chamber operator.

....snip....

Dr. Deco - do you have any info on this "competing" theory?

Thanks!

- Kent

I think he's referring to some ideas developed in the field by the WKPP. I've seen some short articles (more like emails actually) indicating that some divers making shallow bounces to pick up gear after a long exposure were getting bent on a regular basis where (it is assumed) they otherwise wouldn't have been.

The theory put forth to explain that was that bubbles present in the lungs were getting shunted to the arterial system because of the compression during the bounce. I think the theory came from Parker Turner and with a last name like that he must have been right....

It seems to me that I also read somewhere that the WKPP dives deeper and longer on repetative dives to "reset" (is the word I remember) before deco-ing out from the second dive. I'll add that I'm not 100% sure I understood that correctly at the time but it sounds like what Scubadad is saying.

In any event, I rather doubt that the experience of the WKPP making extremly deep and long dives has much application in the world recreational diving. Nevertheless, the observations are still very interesting.

R..

 

[Mako Mark]

I think he's referring to some ideas developed in the field by the WKPP. I've seen some short articles (more like emails actually) indicating that some divers making shallow bounces to pick up gear after a long exposure were getting bent on a regular basis where (it is assumed) they otherwise wouldn't have been.
R..

You are talking about GI3 I believe:

http://www.innerrealm.co.nz/dir_details.asp?pk=41