Northwest Dive Club

I was reading an article posted on the ADM website under the 'Free Web Articles' section entitled 'RGMB'. The author makes a comment that
"Sir Leonard Hill's work is called the "Critical Pressure Hypothesis". Sir Leonard Hill first questioned the wisdom of staged decompression vs. continuous uniform decompression since body tissues are more likely to act in an "analog" than a "digital" manner. This would appear very similar to the saturation tables that were developed by Lambertsen and others that are still in use today."
I'm having a hard time understanding what the author means when he says "since body tissues are more likely to act in an "analog" than a "digital" manner.".... I'm hoping someone could help clarify that statement for me.

Thank you in advance.

I believe what the author was trying to say is that your tissues do not offgas in the fashion of a step function. The gas will be coming out of your tissues at a rate better represented by some smooth function (analog).

In this context digital off-gassing would be something like: Ascend then Offgassing is ON until some critical point is reached, then Offgassing stops (OFF) until you ascend to the next staged stop where it turns on again. The human body doesn't really operate in an ON/OFF digital mode, it's a set of smooth functions.

Most decompression algorithms divide the body up into steps of tissues and assign a half-life (or bubble tension) to each of those cells. That could be what the author meant, or he could be referring to the way we stop every ten feet for decompression. Both represent digital steps rather than a continuous analog (parabolic curve). Decompression would probably be much more efficient if we could actually just slowly decrease our ascent rate from 10 fpm, to 9 fpm to 7 fpm, etc.

Rather than a 5 minute stop at 30' and 12 minutes at 20', it might take you four minutes to go from 40' to 30' and then ten minutes from 20' to 10', etc. Just a guess?

That makes sense Jake. I guess I've never really looked at decompression as an 'On or OFF' mechanism so the wording seemed strange to me. In that light I can see how the above statement would make sense. I've always been of the impression that on gassing and off gassing were a continues event. Though I also understand (I believe) how off gassing (and presumably on gassing) slow down as the gradient becomes narrower, I'd not thought of them as 'stopping' until we are completely saturated or desaturated.

Scott. That seems to play right into Jake's take on the meaning as well.
Thanks guy's I think I got it.

I think this is a pretty good summary. Of course, if I were to do this, I probably couldn't hang on the deco trapeeze like a monkey and watch movies on my ipod.

boydski wrote:Most decompression algorithms divide the body up into steps of tissues and assign a half-life (or bubble tension) to each of those cells. That could be what the author meant, or he could be referring to the way we stop every ten feet for decompression. Both represent digital steps rather than a continuous analog (parabolic curve). Decompression would probably be much more efficient if we could actually just slowly decrease our ascent rate from 10 fpm, to 9 fpm to 7 fpm, etc.

Rather than a 5 minute stop at 30' and 12 minutes at 20', it might take you four minutes to go from 40' to 30' and then ten minutes from 20' to 10', etc. Just a guess?