Deco with too less air, options from the book

[orange_diver]

Pete,

Get a second computer, forget Ratio Deco, and use desktop software to make modern tables as a backup.

Do not get on the bus to hell. It is an express, and you will know a lot of people already there.


CHeers

JC

hey John

i'm a big fan, glad to see you on SB. i happen to use ratio deco, i'm curious what your experience with it has been and your objection to it.

thx

 

[nereas]

BJ,

I don't get it? I must be out of touch...... agian.

I don't think I have to apologize to the rest of the world, but I am with you. I love dive computers. What is not to love? They have come a long way from the ScubaPro Deco Meter, but to tell the truth I even liked that thing?

I will generally use one computer and a depth gauge/timer with a table in my pocket, or two computers (and probably still carry a table) on a serious dive. For comparison on Britannic, it was the Vision electoronics, a VR3, and a table.

By the way, I somethimes have to lie to my computers to get us all on the same page, but that is another thread probably?

My new favorites are the Shearwater, and the VRx, for a bunch of reasons. I don't like crap computers, or crap anything else in diving for that matter?

If somebody does not want to dive a computer, then please go with what works for you, but computers work for me.

Do I get flamed, tarred and feathered now? Can I share some flame and tar with you as well?


Cheers

JC

Love your articles in Scuba Diving magazine!

They are the Aesops Fables of scuba.

They always leave the reader wondering "what was this diver thinking?"

 

[nereas]

This from Dick Vann the head research Guru at DAN: Sorry I still can't do the MQuote thing yet?

Hi John,

Yes, indeed. This is known as acclimatization or adaptation to decompression. The literature is not extensive, but I reviewed what is available on pgs 138-139 in Chapt 7 of BoveÃÔ 2004 (4th ed) Diving Medicine text. Work up dives seem to be very helpful in reducing DCS risk.


Happy New Year,


Dick



From: John Chatterton [mailto:jc@johnchatterton.com]
Sent: Monday, January 12, 2009 9:24 AM
To: Denoble, Petar; Vann, Richard
Subject: Ramp up dives


Gentlemen,

I hope all is well with the both of you guys these days.

I have a decompression question? I have come to believe that prior to a big deep dive such as Britannic, divers benefit from ramp up dives? These are defined as dives to promote good off and on gassing conditioning. This would be opposed to not diving for a couple of weeks prior to the Big Dive. Are you aware of any research that might support, or refute this??



Cheers

JC

Thank you for the update.

I always believed that "ramping up" was more of a matter of readjusting your mixes to your current level of fitness for deco. This new twist is somewhat more fascinating.

 

[nereas]

We all don't have the same goals with our diving, dive the same gases, or use the same equipment. The dive computer is just another tool, and its strength is that it can address a wide specrum of needs.

Most of what I know about decompression and technical diving, I have learned from using desktop software to generate dives in the comfort of my home, and then watching my dive computer on real dives.

The dive computer is a powerful tool, but it is not a substitute for experience, planning, education or intellignece.

Cheers

JC

What caveats are you aware of regarding the DiveRite NiTek HE ?

I have heard at the local dive shop that DiveRite has stopped making them and is developing a new one for decompression trimix diving.

I have not heard why, nor have I heard what was "wrong" with the former model.

 

[Dtaine]

Yes, indeed. This is known as acclimatization or adaptation to decompression. The literature is not extensive, but I reviewed what is available on pgs 138-139 in Chapt 7 of BoveÃÔ 2004 (4th ed) Diving Medicine text. Work up dives seem to be very helpful in reducing DCS risk.

Most of the understanding of acclimatization comes from mountaineering where climbers have to deal with lower atmospheric pressure. I'm no doctor, but from everything I know about it the body responds to the decreased pressure by producing more red blood cells to deliver oxygen throughout the body more efficiently.

The problem is, most of the knowledge is about decreased pressure in mountaineering, not increased pressure related to scuba diving. Considering most divers won't be going deeper than 3 or 4 ata's on a regular basis I doubt there's any real research on the subject of any help to scuba divers. Needless to say though, the work referenced in what I've quoted above has definitely made it's way to the top of my reading list.

 

[seaducer]

Most of the understanding of acclimatization comes from mountaineering where climbers have to deal with lower atmospheric pressure. I'm no doctor, but from everything I know about it the body responds to the decreased pressure by producing more red blood cells to deliver oxygen throughout the body more efficiently.

I thought altitude sickness had more to do with reduced oxygen levels, as opposed to reduced pressure.

The changes in atmospheric pressure are much greater for scuba as opposed to climbing even an 8000 meter peak. Consider that at 33 ft/10m you double the atmospheric pressure from ~14.7psi to ~29.4 psi, where as climbing to the top of Everest is not reducing the atmospheric pressure the same ~14 pounds reverse. Even if the pressure is half that of sealevel, that is only a ~7psi difference...

 

[Dtaine]

I thought altitude sickness had more to do with reduced oxygen levels, as opposed to reduced pressure.

The changes in atmospheric pressure are much greater for scuba as opposed to climbing even an 8000 meter peak. Consider that at 33 ft/10m you double the atmospheric pressure from ~14.7psi to ~29.4 psi, where as climbing to the top of Everest is not reducing the atmospheric pressure the same ~14 pounds reverse. Even if the pressure is half that of sealevel, that is only a ~7psi difference...

I believe there are reports of climbers breathing oxygen who have still gotten altitude sickness.

There's the old saying that if you could be taken by some magical helicopter from sea-level to the top of Mt. Everest you would die in a matter of minutes. Would this be true if the person was breathing pure oxygen the whole way? Perhaps, but I don't know, and I doubt you would find anyone to try it in a chamber.

AMS is just about as confusing as DCS, it's a sliding scale of gray that we do our best to understand.

Personally, I'm skeptical at any claims that divers can acclimatize to greater pressures through subsequent dives. There might be an effect, but science hasn't determined that yet.

 

[Gilldiver]

There's the old saying that if you could be taken by some magical helicopter from sea-level to the top of Mt. Everest you would die in a matter of minutes. Would this be true if the person was breathing pure oxygen the whole way? Perhaps, but I don't know, and I doubt you would find anyone to try it in a chamber.



It was done many times by B-17 and B-24 crews in WWII. Base was at or near sea level and bombing altitude was in the 20-25,000 foot range. But the duration at altitude was only 5 to 12 hours per mission.

It has more to do with time at altitude, the pp of O2 at altitude, and may have a low CO2 component - it is not well understood.

Some altitude sickness may have fluid collecting in the lungs, drowning on a mountain top.

Altitude sickness - Wikipedia, the free encyclopedia

But back to what John was talking about - diving. John, perhaps we were doing a lot more then we thought back in the 80's when we would "Work Up" to the Doria and other deep dives. I always thought we were just working up on the Narc issues.

 

[Dtaine]

There's the old saying that if you could be taken by some magical helicopter from sea-level to the top of Mt. Everest you would die in a matter of minutes. Would this be true if the person was breathing pure oxygen the whole way? Perhaps, but I don't know, and I doubt you would find anyone to try it in a chamber.

It was done many times by B-17 and B-24 crews in WWII. Base was at or near sea level and bombing altitude was in the 20-25,000 foot range. But the duration at altitude was only 5 to 12 hours per mission.

I didn't think about that, interesting. Like I said, I'm not a doctor.

It has more to do with time at altitude, the pp of O2 at altitude, and may have a low CO2 component - it is not well understood.

Some altitude sickness may have fluid collecting in the lungs, drowning on a mountain top.

Right, that would be HAPE, anyone interested can find more here: Base Camp MD - Guide to High Altitude Medicine

Altitude sickness - Wikipedia, the free encyclopedia

But back to what John was talking about - diving. John, perhaps we were doing a lot more then we thought back in the 80's when we would "Work Up" to the Doria and other deep dives. I always thought we were just working up on the Narc issues.

Perhaps you were, I was just pointing out that there isn't really any proof or research about it.

 

[Gilldiver]

Back in WWII you had 10 men per large bomber crew, a 100 plane raid had 1,000 "tests," the 1,000 plane raids had 10,000 "tests" in one day

One of the reasons for going on O2 as they passed through 10,000 feet back then was to avoid black out, but the main reason was to start breathing down the N2 in the blood. The Bomber and Fighter crews could get bent at high altitude.