on gassing vs off gassing

[Dr Deco]

Dear AquaTech:

On Gassing With Exercise

Indeed, you will on gas more with exercise. Dive tables for commercial work are always tested with working test subjects because the tables are for working divers. They are also tested with resting subjects because it was not believed that half times could be modified.

A few years ago in Cozumel, several divers had to fight a very big current and five or six in the small group got the “bends. “ (I do not have the details, but I am sure some of our readers do.) They all needed treatment. Heavy exertion at depth promotes gas uptake. Unfortunately, this is not adjusted or compensated in tables or meters. The halftimes are unaltered - - all of them. There do not exist any adaptive algorithms for this type of dive.

Taking a motor trip

Diving, to me, is somewhat like an auto trip. This consists of two parts. One is using the map (or GPS) to determine where you are and what route you will take. This is similar to the dive table portion of a dive.

The second aspect is the actual control of the car on the road. This you must perform yourself; no map or GPS will actually steer the car. This is similar, in this analogy, to dive technique. Did I on-gas more than would be considered acceptable by the table designer (there are no “adaptive algorithms," yet). Am I moving my limbs to promote blood flow during off gassing? Am I attempting to control micronuclei formation to give myself the best advantage?

Exercise at the stop

Bicycle-like activity with the legs and moving the arms is good for blood flow during the stops. We use this technique at NASA to assist in off gassing prior to “space walks” (EVA). Resting during the stop is almost equivalent to sleeping during the surface interval.

CO2 Buildup

It is true that carbon dioxide decreases in the arterial system during exercise. However, at the tissue level, it increases, and causes an opening of the pre-capillary sphincters (muscle “gates”) to allow more blood to flow to tissues. This buildup of CO2 promotes blood flow along with central neural control (brain), heart rate increase, the “muscle pump,” adenosine diphosphate increase, etc.

Dr Deco :doctor:

 

[DocVikingo]

For those who may be interested, BillP has intimate knowledge of this event.

Just out of interest, here's a paragraph from an "Undercurrent" http://www.undercurrent.org/ article I did comparing dive accident policies last year. It's about one of the divers actually caught in that big, roller coaster current:

"I recently saw a bill from a hyperbaric facility on Cozumel for the treatment of unexpected, uncomplicated DCS sustained in an unexpected wild current ride. La cuenta? Two Table 6, two Table 5 treatments plus related expenses=US$14,050.10. Had this hapless diver sustained injuries so severe that they couldn’t be addressed on island and required air evacuation to Mercy Hospital in Miami, transportation alone would have cost from $10,000 to $20,000 depending on logistics."

Best regards.

DocVikingo

 

[AquaTec]

Doc
thanks for the input.
my favourite way to deco is swimming along a wall

however if i am hanging i generaly do the bicyciling technique
or even jumping jacks. this also helps to stay warm on those 2+ hour dives

then if i am with a group i spend he surface time explaining why

 

[The Iceni]

Dr Deco once bubbled...
Dear AquaTech:

On Gassing With Exercise

Indeed, you will on gas more with exercise. . . A few years ago in Cozumel, several divers had to fight a very big current and five or six in the small group got the “bends. “ (I do not have the details, but I am sure some of our readers do.) They all needed treatment. Heavy exertion at depth promotes gas uptake. Unfortunately, this is not adjusted or compensated in tables or meters. The halftimes are unaltered - - all of them. There do not exist any adaptive algorithms for this type of dive.
Dr Deco :doctor:

I am not sure Bruce Wienke would agree and would be interested in his comments. I am saving my pennies to buy myself a Hydro Space Explorer precisely because it does include adaptive algorithms. I do not believe the alorithm can be reselected during the actual dive but the diver can select for both assymetrical on-gassing/offgassing and variable RGBM according to the activity proposed for the dive, from a relaxed warm-water dive to a heavy activity cold-water dive. In the latter case the "conservatism" is increased by assuming offgassing ("relaxing" on a trapeze for example) can be delayed by up to 30% compared with the more rapid ongassing experienced during the working part of the dive.

As for Jon lines, as I understand it few British divers regularly plan to hang on a shot in, or fin against, a current;- preferring instead to arrange for the boat to follow a trapeze, lazy shot or SMB - "going with the flow". I suspect this may lead to fewer such unexpected incidents of DCI when extended periods of deco run into the time of rapid tidal current flow.

 

[Spectre]

Dr Paul Thomas once bubbled...
I am saving my pennies to buy myself a Hydro Space explorer precisely because it does include adaptive algorithms

Hmm... that brings up an interesting thought. I wonder if there are, or are plans in the work for, an Air Integrated computer that attempts to corrallate SAC rates with exertion levels, and adjusts for it. Of course that would make gas management planning hell

Eh.. just thinking out loud...

 

[The Iceni]

er. . On which cylinder/set would you propose to put the single transmitter, Spectre?

Travel gas, bottom mix, or one of the various deco mixes? Or are you suggesting multiple transmitters, each one of which could fail?

 

[Spectre]

Dr Paul Thomas once bubbled...
er. . On which cylinder/set would you propose to put the single transmitter, Spectre?

Yea.. good point. It was just a thought... *shrug* I don't like AI anyway...

 

[Dr Deco]

Dear Paul and Spectre:

“Adaptive” algorithms

If the Hydro Space Explorer can do these things, then that would be an adaptive computer.

The truth is, everyone has a different response to the nitrogen load. This is measurable in a laboratory setting for both hypobaric and hyperbaric cases. When a table is designed, it is safe for [let us say] at but 2% of the population. That means that 98% were able to decompress without incident. In truth, many could endure a much larger gas load.

It is always tempting to make a computer or model that will do wonders. Those who have performed laboratory experiments know that the situation is simply a lot more variable. Brian Hills, a noted barophysiologist, once remarked, “The day I watched a bubble grow in one capillary and another bubble shrink in the capillary next to it, that was the day I gave up designing tables.”

I know that people love these devices and will continue to discuss them.

Air Integrated

If one could actually measure true oxygen consumption during on gassing and off gassing, that would be of great interest. It would not eliminate the fact that DCS incidences are very low to start with.

Dr Deco :doctor:

 

[Uncle Pug]

please talk about:
"cavitation and micronuclei formation"
in relationship to the subject of this thread.

 

[The Iceni]

Dr Paul Thomas once bubbled...
As for Jon lines, as I understand it few British divers regularly plan to hang on a shot in, or fin against, a current;- preferring instead to arrange for the boat to follow a trapeze, lazy shot or SMB - "going with the flow". I suspect this may lead to fewer such unexpected incidents of DCI when extended periods of deco run into the time of rapid tidal current flow.

= less micronuclei NOT more ongassing. The offgassing at the stop will be the same if the diver is doing the same, whereas the ongassing at depth is greater when the diver is active AT DEPTH. Thus the relative differences in half times and the theory of asymmetrical diffusion, which is a completely separate issue from micronuclei formation.

The Explorer manual is available in PDF format at
http://www.hs-eng.com/Explorer Manual M.PDF the adaptive pre-dive conservatism feature is shown on page 11.

That's my understanding, Uncle Pug.

Am I right Dr Deco?