VPM vs BUHLMAN

[JeffG]

In one sense, Buhlmann has 100 years of research behind it, and VPM is but a few years old!
Don 't you think that this is a nice reason to prefare Buhlmann?

Using that thinking, the earth would be a flat disk in the center of the universe.

 

[TSandM]

There was a lovely article in Diver magazine a couple of years ago by Dr. David Sawatzky, who writes extensively about diving medicine and about DCS. The observation he made at the end of the article really stuck with me . . . He said that the big improvement in DCS was made with Haldane's original observation about ratios, and that everything we have done since is fiddling with the edges.

On the one hand, very few people get bent in comparison to the number of people diving. On the other hand, people still get bent when their profiles were computed by acceptable means, and executed perfectly. Which means we still don't have it "right". Pure dissolved gas models (Buhlmann) may seem reasonable to you, and many people still use them without issue. Bubble-based models may end up being "better", but it takes time and a lot of dives to know for sure. And everything is confounded by individual variability and dive-condition dependent variables as well.

 

[MXGratefulDiver]

There was a lovely article in Diver magazine a couple of years ago by Dr. David Sawatzky, who writes extensively about diving medicine and about DCS. The observation he made at the end of the article really stuck with me . . . He said that the big improvement in DCS was made with Haldane's original observation about ratios, and that everything we have done since is fiddling with the edges.

On the one hand, very few people get bent in comparison to the number of people diving. On the other hand, people still get bent when their profiles were computed by acceptable means, and executed perfectly. Which means we still don't have it "right". Pure dissolved gas models (Buhlmann) may seem reasonable to you, and many people still use them without issue. Bubble-based models may end up being "better", but it takes time and a lot of dives to know for sure. And everything is confounded by individual variability and dive-condition dependent variables as well.

Certainly I'm no expert ... but based on what I understand about decompression it's unlikely we will ever get it "right". Dissolved gas and bubble models are just that ... models. They're based on assumptions that know nothing about the factors that affect them ... namely your individual physiology ... and are therefore based on an "ideal" physiology that somewhat emulates yours and mine.

Predicting decompression is much like predicting weather ... and for similar reasons ... they're both based on the interaction of factors that will vary from day to day ... and those variations will produce different results due to the way they react with each other.

People talk about "undeserved hits" ... when in fact there is no such thing. All decompression models do is provide you with a profile that's considered "acceptable risk" ... but the risk is always finite, and sometimes it's going to catch you on a bad day.

The best approach is still to understand the basics of how decompression affects our body, and the fundamental assumptions behind each decompression model available. Run a few test profiles, view them from the perspective of your own personal "risk factors", and create your own profile based on the available information.

The worst approach is to trust a computer ... be it one you're wearing during the dive or the one you use to run a deco program ... and accept the data without really understanding why the numbers come up the way they do ...

... Bob (Grateful Diver)

 

[knotical]

The worst approach is to trust a computer ... be it one you're wearing during the dive or the one you use to run a deco program ... and accept the data without really understanding why the numbers come up the way they do ...

Agreed.
The best dive computer is the one between your ears.

 

[nereas]

Agreed.
The best dive computer is the one between your ears.

This statement is only true for relatively shallow dives.

 

[Rainer]

Or people with something between their ears.

 

[BOTTOMTIMER]

Dear JeffG.

It was very kind of you to try to write something.
I wrote about 100 years of RESEARCH. That means that this is something that they are working with all these years, so thy have backround. What is the backround of VPM? If you take a look at Mark 's Ellyatt dives (before the recor) with VPM you will see that he bend BEFORE he come out to the surface.
Can you please validate your theory?

Regards

 

[nereas]

...Nereas wrote that he has done dives to 75m. So he used He.

What is going on with this gas that goes to the tissues faster. Is it a good idea to do deep stops in dives up to 60m. I am saying this because i think that because helium goes faster in the tissues, it comes out the same fast. So do i decompress or isteel ceep gas in my tissues?

...

Helium is believed to dissolve faster into blood and tissue, yes. And it is also believed to permeate out of blood and tissue faster as well, indeed. (The common vernacular of non-chemists is "on-gas" or "off-gas.")

The main considerations in diving with helium are therefore (1) to work with an effective decompression model, and (2) to make sure that you hold to your decompression stops, since an inadvertent immediate ascent to the surface would likely be fatal, with helium.

If you have never dived with helium before, then your instructor will want to make sure that you have good buoyancy control and good deco stop procedure under simulated deco before he/she lets you use helium.

There are a host of deco tables, models, and programs that have been designed specifically for helium mixes.

 

[Rick Inman]

This statement is only true for relatively shallow dives.

Can you define "relatively shallow"?

 

[MXGratefulDiver]

Can you define "relatively shallow"?

A dive where your deco plan consists of standing up ...

... Bob (Grateful Diver)