Depth Blackout

[Lou]

Quote: (Originally Posted by Kevrumbo)

"Helium is our Friend. . ." GI3

How does this link to CO2 narcosis, when the CO2 comes from the O2 portion of the gas you are breathing, not the N2 portion? Why is it pertinent to air dives and not trimix, even if skip breathing is done when breathing trimix? I am not sure I understand the physiology here.

[Clare Gledhill]

Quote: (Originally Posted by Lou)

How does this link to CO2 narcosis, when the CO2 comes from the O2 portion of the gas you are breathing, not the N2 portion? Why is it pertinent to air dives and not trimix, even if skip breathing is done when breathing trimix? I am not sure I understand the physiology here.

Anything with increases the work of breathing will increase potential CO2 production/retention. Both our respitory systems and our equipment work more eficiently with lese dense gas. Breathing heliox at 100 meters gives about the same WOB as air at 30 metres.

[Lou]

Quote: (Originally Posted by Clare Gledhill)

Anything with increases the work of breathing will increase potential CO2 production/retention. Both our respitory systems and our equipment work more eficiently with lese dense gas. Breathing heliox at 100 meters gives about the same WOB as air at 30 metres.

OK, so WOB I get, but that is a fractional contributor compared to physical extertion, surely, so although He makes it less likely, on a common baseline, it doesn't mitigate the risk any where near entirely.

I took Kev's reply as indicating it wouldn't happen with trimix. I must have read his meaning wrongly.

[TobyFish]

Quote: (Originally Posted by Brian A)

There also seems to be something else in play in that the 2 examples sited here (mine and LCFs) are also where the diver is doing there deepest dive to date, suggesting that there could also be a bodily reaction to stress or "first nacosis" perhaps?

Perhaps, but that's a bit of a leap. The simpler explanation would be that it's a purely depth-dependent phenomenon for which people have differing tolerances. In that case ti would happen on your deepest dive so far (for the same reason that your car keys are always in the last place you look).

As a big fan of Occam's Razor I'd favour the simpler explanation.

[Marijn]

Quote: (Originally Posted by Lou)

OK, so WOB I get, but that is a fractional contributor compared to physical extertion, surely, so although He makes it less likely, on a common baseline, it doesn't mitigate the risk any where near entirely.

I took Kev's reply as indicating it wouldn't happen with trimix. I must have read his meaning wrongly.

Well, the combination of: increased work because of the current, higher WOB because of air @ 30m and possibly not exhaling properly CAN lead to a build-up of Co2.

WOB is mentiont in several texts I've read to be the cause of less than proper exhalation, leading to Co2 retention.
If I'm not mistaken it's also mentiont in the GUE tech1 manual, and it has some reference material as well.

Now I'm going out on a limb, but isn't narcosis exacerbated by Co2 levels?
And could this lead to a level of narcosis high enough to reach "anaesthetic" levels?

Just thinking out loud here.
If there's any flaws in these thoughts, just lemme know please

[Ahmed Adly, Marlin Inn DC]

Back in the good old days of deep diving, I had a friend who used to black out all the bloody time. It was very anoying.

He survived his diving days due to daily miracles and some help from his friends.

[Ahmed Adly, Marlin Inn DC]

Quote: (Originally Posted by Martin Burnard)

Due to its similarity with narcosis, there is probably an opportunity for cross pollination of ideas, but that requires somebody with detailed knowledge of both areas to identify.

The problem is that the people who study this are in an age group that dose not permit any kind of polination

[LauNar]

Quote: (Originally Posted by TobyFish)

Perhaps, but that's a bit of a leap. The simpler explanation would be that it's a purely depth-dependent phenomenon for which people have differing tolerances. In that case ti would happen on your deepest dive so far (for the same reason that your car keys are always in the last place you look).

As a big fan of Occam's Razor I'd favour the simpler explanation.

I'd move even a bit further and look into depth-independent stuff, ie. why people faint/blackout on dry land. There are lots of factors that could be present on a dive and cause a fainting, others than just narcosis: stress/fear (esp. with newbies), shallow or skip-breathing, low blood sugar, low blood pressure (tight neck seal maybe?), cardio problems etc.

[Ahmed Adly, Marlin Inn DC]

Quote: (Originally Posted by LauNar)

I'd move even a bit further and look into depth-independent stuff, ie. why people faint/blackout on dry land. There are lots of factors that could be present on a dive and cause a fainting, others than just narcosis: stress/fear (esp. with newbies), shallow or skip-breathing, low blood sugar, low blood pressure (tight neck seal maybe?), cardio problems etc.

Is it common to find people lying around on the street unconcious with open eyes (scaring the shit out of little children)?

[Kevrumbo]

Quote: (Originally Posted by Marijn)

Well, the combination of: increased work because of the current, higher WOB because of air @ 30m and possibly not exhaling properly CAN lead to a build-up of Co2.

WOB is mentiont in several texts I've read to be the cause of less than proper exhalation, leading to Co2 retention.
If I'm not mistaken it's also mentiont in the GUE tech1 manual, and it has some reference material as well.

Now I'm going out on a limb, but isn't narcosis exacerbated by Co2 levels?
And could this lead to a level of narcosis high enough to reach "anaesthetic" levels?

Just thinking out loud here.
If there's any flaws in these thoughts, just lemme know please

Dr. Jolie Bookspan , author of Diving Physiology in Plain English, writes from her article Supra:

"Carbon Dioxide retention is now viewed as a contributor to oxygen toxicity and nitrogen narcosis, suspected as a contributor to decompression sickness, and implicated in incidents of underwater confusion and loss of consciousness."


Also regarding deep air resulting in greater CO2 accumulation than helium based mixtures, she describes a U.S. Navy Experimental Diving Unit study performed in 1958, whose results were reconfirmed in 1995:


"Continued work made it clear that while breathing nitrogen-oxygen mixtures at depth, carbon dioxide retention occurred, whereas with helium-oxygen, ventilation was essentially unimpaired and CO2 levels stayed close to normal."