PADI Dive Tables

[Dr Deco]

Dear Mike:

I do not know too much about the instructional aspects of PADI. Possibly, they teach 60 feet/minute for ascent since their tables were tested for this. Should one so desire, it would be all right to ascend at a slower rate of 30 feet/min. This would not make the table more dangerous because it was outside of the test limits. This would only be a problem is the ascent was very rapid.

It is true that a patent foramen ovale (PFO), and well as age and poor physical fitness contribute to increase risk of DCS. I do not believe, though, that these are particularly influential factors. They are often given as such, however.

I am of the mind in the recent ten years that excessive musculoskeletal activity on the surface is the greatest determinant of DCS. In our studies at NASA concerning DCS at 1-g (ground simulations) and DCS in 0-g (during EVA), we found that physical activity played a very big role. Gas loading was, naturally, the biggest factor, but after that, it was activities that required strength when moving. This was either with the arms or with legs, and changed the DCS incidence often by a factor of ten fold!

Dr Deco.
:doctor:

 

[Lost Yooper]

"excessive musculoskeletal activity on the surface is the greatest determinant of DCS"

You're talking about people who physically exert right after a dive, right?

If so, it seems to me that this is yet another reason that traditional tables based on Haldanean models are becoming rather unpopular for technical divers. Since there are tables and techniques that can severely limit the amount of bubbles in your system after a dive (virtually all bubbles in less than just a couple hours for most people), it makes me wonder why the continued use of the tables.

Curiosity!

Mike

 

[ghof]

DR Deco


I have read tons on deco. Is it your opinion that NDL tables are entirely adequate for recreational divers? And for the techies do you have a deco program that you find adequate for extended range mixed gas diving?


GHOF, aka Mike

 

[CheeseWhiz]

Is it possible to quantify "excessive musculoskeletal activity"?

Is climbing a set of stairs in full dive gear excessive?

Is riding a bicycle 5 miles excessive?

Is doing any work at all once you return home excessive? (Please say yes !!:tease: )

CheeseWhiz

 

[Dr Deco]

Dear Yooper:

1. When I speak of tissue nuclei generation, I am considering heavy physical activity for an hour or two after the dive. I believe that this is the cause of many “undeserved” hits.

2. When you allude to tables for technical divers, I believe that the big distinction is in how these are used in actual diving practice. Technical divers typically use varying gas mixtures of helium, nitrogen, and oxygen. The tables developed by the various naval services do not treat these mixtures, and so technical divers have gone to the algorithms developed by Professor Buhlmann. These so-called “Swiss tables” are based on Haldane principles, and they have an advantage that they have been laboratory tested. When a table has been tested, you have an idea that it works on a practical basis but no proof that the theory behind it is correct. The latter can only be accomplished by an experiment designed to directly test the algorithm’s underlying hypothesis.

One primary, new addition to algorithms of the non-Buhlmann type is the insertion of deep stops. These were originally advocated by Brian Hills PhD (in the 1960s) to prevent supersaturation and gas phase separation during ascent. This phase separation was postulated to occur on hydrophobic surfaces in tissues, and made the transition from the dissolved gas phase to the free gas phase easier. It is now believed by some of us that this concept is not correct. Rather, preformed tissue micronuclei exist in tissues. Their existence was first postulated by Edmund N. Harvey PhD in 1928 and applied by him to decompression during WW II. These nuclei, he conjectured, are created by fluid motion ( hydrodynamic cavitation ).

We now arrive at a juncture. In the original VPM algorithm created by David Yount PhD and his coworkers, the nuclei are intrinsic to the system. They shrink with compression (during the descent) and grow by inward diffusion of gas during decompression. The radii of the bubbles are not influenced by musculoskeletal activity (that is, forces that produce hydrodynamic cavitation). In addition, many barophysiologists today do not really believe in the existence of tissue micronuclei (or at least only give it a passing nod) and continue to use the critical supersaturation concepts of Haldane.

The idea of deep stops has, in addition, not been tested in controlled laboratory studies, although there do exist some data to suggest that the idea is correct. This includes work of Hills and dive trials in Germany.

Thus, there can be several reasons why deep stops and non-Haldanian algorithms are not used. I personally believe in deep stops, micronuclei, creation of them through musculoskeletal activity, and reduced dissolved gas elimination when microbubbles are present in tissue. These viewpoints are based on extension of my research at NASA. They represent my views and are not necessarily shared (or understood) by many individuals within NASA.

Since tables for recreational divers do not include stops (excepting the “safety stop”), deep stops do not have a meaning. Technical divers make their own choices concerning what methods they will employ for decompression.

Dr Deco :doctor:

 

[Lost Yooper]

Ok, doc. Let me digest this for a little bit so can I can ask another question.

This stuff tickles me pink.

Mike

 

[Dr Deco]

Dear GHOF:

1. I do believe that the NDLs for recreational divers are fine. I do add this caveat, though. In the testing of these tables, the subjects were relatively quite while on the surface. None moved heavy scuba tanks, or climbed ladders as a part of the test protocol. None played beach volleyball and none went free diving. If this had been a part of the activity during the surface interval, I believe that the NDLs might have been revised to shorter durations.

Therefore, divers who participate in these stressful activities are not doing what was done during the test conditions. In the PADI table test series, the subjects did walk around between dives, but that was as stressful as it got was. Remember that this observation of the full range of activity and risk of DCS did not become noticed until we at NASA started to investigate the risk (or lack of) decompression sickness in null gravity situations. This has changed my thinking considerably in the last ten years.

2. As far as decompression schedules for technical divers goes, I do not have any opinions on this. At NASA we do not investuigate deep diving situations and my personal knowledge in this area is not adequate.

Dr Deco

 

[BillP]

Originally posted by Dr Deco

I personally believe in deep stops, micronuclei, creation of them through musculoskeletal activity, and reduced dissolved gas elimination when microbubbles are present in tissue.

The "Apostles' Creed" of the Microbubblists?

Sorry, couldn't resist. (grin)

Bill

 

[Dr Deco]

Dear Bill:

As a matter of fact, I noticed that too. Right after I wrote it!

Mike P.

 

[Dr Deco]

Dear CheeseWhiz:

Musculoskeletal activity includes any movements of the upper or lower extremities. This is not excessive if it only includes walking, since all tables have been tested when the subjects were walking in unit gravity (schedules for astronauts are tested in simulated 0-g).

Climbing stairs would be considered excessive. (I have not tested this in diving situations but it certainly would be bad in altitude decompression where it HAS been tested.) Riding a bicycle is also excessive. And so is beach volleyball.

As for work several hours after you arrive at home, that is way out of the danger zone. Nice try, though!

Dr Deco