SAC, air vs. nitrox

[TSandM]

I can't find the original paper I read, but this one also presents the same conclusion, and I suspect that the full text with references would be useful as well:

[abstract] DONALD

There are several others I scanned while I was looking, that confirm the idea that hypercarbia is less symptomatic in the presence of elevated ppO2s. The question of mental clarity on Nitrox might be related to this, or it could be that Meyer-Overton is overly simplistic and that oxygen is not as narcotic as nitrogen. I treat it as though it is because I want the additional safety, and I'm narcosis-prone anyway.

 

[Dirty-Dog]

The espressos might help with O2 tox, but I can't help but think it's likely the 280 heart rate and constant twitching might have a negative impact on SAC and bouyancy...
:rofl:

 

[turnerjd]

The espressos might help with O2 tox, but I can't help but think it's likely the 280 heart rate and constant twitching might have a negative impact on SAC and bouyancy...
:rofl:

Coffee-screen-interface!

However for 30 seconds seriouseness, I suspect that the caffeine addicts amongst will probably take in more caffeine before a mornings diving than used in the study. They used 1.25, 2.5, and 10mg/kg. Average cafeine consumption is about 7-10mg/kg/day, so I would hate to think what it would be like in heavy coffee drinkers. [/end serious]

Jon

 

[Rick Murchison]

... or it could be that Meyer-Overton is overly simplistic and that oxygen is not as narcotic as nitrogen...

I think the fact that oxygen is both metabolized and constantly scavenged by hemoglobin reduces free oxygen titre enough to counter much of its narcotic effect. However... I really like SSI's guidance here - "It is best not to assume reduced narcosis from using Nitrox." That's just right, don't you think?

Rick

 

[turnerjd]

As somebody very wise once said:

Assume makes an ASS out of U and ME



Jon

 

[boulderjohn]

I don't think that narcosis is a reason. By high fO₂ I am talking about nitrox 38 or 40 (the max that I can get, MOD nitrox 40 = 25m). I used this regularly when assisting on OW dives. As these are all <18m dives, often with the majority of the dives around 10-12m. I don't think that narcosis comes in. Certainly task loading does.

One of the problems with making a determination is that it is difficult to isolate factors contributing to the SAC rate. The average dive on mixes approaching 40% is likely to be much shallower than on dives on air or lower EAN percentages. I have had AOW students whose SAC goes through the roof when they do the deep dive, probably because of some anxiety associated with those deeper depths. Thus, a more relaxed diver in shallow water is likely to have a better SAC rate. Characteristic diver behavior while assisting on OW dives is likely to be different from characteristic diver behavior on other dives. If you want to make a reasonable comparison, you have to do everything possible to make all other contributing factors the same.

 

[Dirty-Dog]

Coffee-screen-interface!

However for 30 seconds seriouseness, I suspect that the caffeine addicts amongst will probably take in more caffeine before a mornings diving than used in the study. They used 1.25, 2.5, and 10mg/kg. Average cafeine consumption is about 7-10mg/kg/day, so I would hate to think what it would be like in heavy coffee drinkers. [/end serious]

Jon

I think the portion I highlighted is significant. Even if you normally use 10mg/kg/day, taking the entire 10mg/kg in one lump dose is still going to have some impact.

 

[TSandM]

Rick, you nailed it, as usual.

 

[turnerjd]

One of the problems with making a determination is that it is difficult to isolate factors contributing to the SAC rate. The average dive on mixes approaching 40% is likely to be much shallower than on dives on air or lower EAN percentages.

If you want to make a reasonable comparison, you have to do everything possible to make all other contributing factors the same.

Perhaps I didn't make myself clear in that I was comparing dives at the same inland training site. I was DMing for the same qualifications with the same instructor, but with different gas mixes (the different mixes were mostly down to my disorganization in preparing a tank of EANx 40 before going diving)

The nature of the training site (Stoney Cove for those in the UK) means that these were square profile dives and the depths were pretty constant.

Jon

---------- Post added April 18th, 2012 at 07:05 PM ----------

I think the portion I highlighted is significant. Even if you normally use 10mg/kg/day, taking the entire 10mg/kg in one lump dose is still going to have some impact.

Yes and no. IIRC one cup of strong coffee (or a couple of those weak things they sell in Starbucks) is around 80 -100 mg cafeine. So somebody of around 75-80 kgs drinking a double expresso in the morning is approaching the 2.5 mg/kg already. Now, if you're like me and have a double expresso just to get out of bet, plus a thermos of coffee with you when you set off, it is quite possible to be well into the effective doses they used in their study.

The other way of looking at it is that on average we drink three caffeinated drinks per day, so our 7mg/kg/day is 3 doses of 2.3mg/kg (making our total of 7 mg/kg in one day).

Jon

Jon