Dive tables

[BillP]

Hi Dr. Deco:

I have a dive table/physiology question for you. How does a diver who is a "K" diver (for example) on his tables at the end of a single dive differ physiologically from a diver who is a "K" diver at the end of a surface interval? How do those divers differ physiologically from a diver who is a "K" diver after a series of multiple repetitive dives?

For example (from PADI's RDP), Diver A makes a 40' dive for 48 minutes and is a "K" diver at the end of his dive. How does he differ physiologically from Diver B who makes a 40' dive for 85 minutes (an "S" diver) and then has a 35 minute surface interval (now a "K" diver)? Or do they differ?

I welcome input from other board participants too.

TIA,

Bill

 

[Dr Deco]

Bill:
This is a very interesting question, and its answer is not simple. In the original Haldane formulation of decompression tables, the pressure (concentration) of dissolved gas in the tissues was the only variable that mattered. We know today that there are different physiological factors that can modify the elimination of gas from the tissues as Diver A and B both become “K” divers.

In the first place, the repet designators are for only one compartment halftime, namely, the one that controls (or monitors) the “dissolved gas status” of the body. This controlling tissue is the longest that the table designers believed would play a role; it is the sixty-minute tissue in the PADI tables. Now there is no difference in gas content in that 60-minute tissue for both diver A and B in your two scenarios. However, the other compartments will have gas contents that differ, but this will not play a role under the conditions of proper table use. A dive computer would track all compartments (and this difference could be shown).

Other factors could enter into the picture, and these are much more complicated, and not treated by divers in the field. They are, however, considered, and closely regulated, in research settings. In the example given, the divers reached their “K” categories after various lengths of time. In the laboratory, we would monitor the divers’ water intake (since this controls hydration and surface tension of the bodily fluids), regulate how much they walked (since this would modify the tissue micronuclei number in the legs), and standardize the general exercise level (since this would modify the heart rate and local blood flow).

All of this is fairly complicated and differs from the simple depth/time-at-depth concepts. Probably we will delve deeper into these topics in the course of this forum.

 

[BillP]

Thanks for the very thorough, yet understandable, answer Dr. Deco. I look forward to delving deeper into deco theory and practice by picking your brain. I'm glad that you're participating in the forum.

Bill

 

[Dr Deco]

If any of the answers are difficult to understand, please ask that a simpler answer be provided --- I will try to adjust the response to that question.