Depth Blackout

[Lou]

Quote: (Originally Posted by Kevrumbo)

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."

So, in fact, this is an argument against trimix at depth and for heliox then.

[Gene_Hobbs]

Lanphier EH (ed). Unconscious Diver: Respiratory Control and Other Contributing Factors. 25th Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 52WS(RC)1-25-82.Bethesda: Undersea and Hyperbaric Medical Society; 1982; 160 pages. RRR ID: 4278

Quote: (Originally Posted by Lanphier and Camporesi. Chapter 5. Respiration and Exertion, In: The Physiology and Medicine of Diving)

1. Higher Inspired Oxygen (PiO2) at 4 ata (404 kPa) accounted for not more than 25% of the elevation in End Tidal CO2 (etCO2) above values found at the same work rate when breathing air just below the surface.
2. Increased Work of Breathing accounted for most of the elevation of PACO2 (alveolar gas equation) in exposures above 1 ata (101 kPa), as indicated by the results when helium was substituted for nitrogen at 4 ata (404 kPa).
3. Inadequate ventilatory response to exertion was indicated by the fact that, despite resting values in the normal range, PetCO2 rose markedly with exertion even when the divers breathed air at a depth of only a few feet.

further references to support the quote above:
Lanphier. Nitrogen-Oxygen Mixture Physiology, Phases 1 and 2. NEDU Report 1955-07. RRR ID: 3326

Lanphier, Lambertsen, and Funderburk. Nitrogen-Oxygen Mixture Physiology - Phase 3. End-Tidal Gas Sampling System. Carbon Dioxide Regulation in Divers. Carbon Dioxide Sensitivity Tests. NEDU Report 1956-02. RRR ID: 3327

Lanphier. NITROGEN-OXYGEN MIXTURE PHYSIOLOGY. PHASE 4. CARBON DIOXIDE SENSITIVITY AS A POTENTIAL MEANS OF PERSONNEL SELECTION. PHASE 6: CARBON DIOXIDE REGULATION UNDER DIVING CONDITIONS NEDU Report 1958-07. RRR ID: 3362

Lanphier. Nitrogen-Oxygen Mixture Physiology. Phase 5. Added Respiratory Dead Space (Value in Personnel Selection tests) (Physiological Effects Under Diving Conditions). NEDU Report 1956-05. RRR ID: 3809

[Gene_Hobbs]

Quote: (Originally Posted by Lou)

So, in fact, this is an argument against trimix at depth and for heliox then.

We must remember that N2 was added back into heliox mixes to potentiate HPNS on deep dives (Atlantis dive series). Most of us have continued to use trimix because it is cheaper but not because it has some advantage.

[TobyFish]

Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC)

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

I take it you've never been to Telford then?

[rjack]

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?

It would be interesting if there were more examples of this relatively shallow blackout.

There are plenty of examples from the free diving world. Although for different reasons.

I'd be interested in knowing if either of your cases had some hyperventilation or breath holding due to cold or stress. Leading to dramatically elevated CO2 which on the surface would be more self limiting but at even slightly elevated PP lead to loss of conciousness. After loss of conciousness the victim then started normal-ish breathing spontaneously but the sum narcosis had not yet dropped sufficiently to regain conciousness.

After ascending the ppCO2+N2 drops and conciousness returns. It may have returned at depth given some extra time. Or it have retriggered some hyperventilation and cycle would begin again.

Richard

[EBT]

Quote: (Originally Posted by Gene_Hobbs)

We must remember that N2 was added back into heliox mixes to potentiate HPNS on deep dives (Atlantis dive series). Most of us have continued to use trimix because it is cheaper but not because it has some advantage.

Although theres also some debate as to the N2 effects supressing the tendency to toxicity (hyper excitation or something, Im a telecomms guy, not a wetware guru).....

...fun all this, isnt it

[Gene_Hobbs]

Quote: (Originally Posted by EBT)

Although theres also some debate as to the N2 effects supressing the tendency to toxicity (hyper excitation or something, Im a telecomms guy, not a wetware guru).....

...fun all this, isnt it

YES, it is fun! This is why I do this for a living and why we started Rubicon for everyone else to join in the fun.

This is an interesting point of debate you bring up. It came up a few months ago and I was caught off guard by it. So, I started looking for works to support/ refute this idea. Oddly enough, I found nothing. Well, they did some work here back in the early 80's that showed N2 suppressing HPNS seizure thresholds (mentioned above) so maybe they did look at O2. This thought prompted several emails to people I would consider experts in the field. ALL of the replies said basically the same thing (with various shades of frustration that people will believe anything). Here is one example:

Quote: (Originally Posted by Peter Bennett)

Never heard this before and I am not sure why he thinks it mght be. True N2 does help to ameliorate HPNS seizures, but O2 seizures are a different mechanism. In fact, in terms of effects on O2 convulsions, I did some animal studies which showed that nitrogen and oxygen (increased density and therefore increased CO2 retention) shortened the time to convulsions in that order. Helium, on the other hand, was best as it was little different from oxygen alone.

[EBT]

Yup, rubicon is probably the best initiative I've seen in a long time, fair play to you for putting the time and effort in.

As for belief, nah... that comes from proof and a certain leap of faith, however an open mind considers information from all quarters. As I said... fun

[Gene_Hobbs]

Quote: (Originally Posted by EBT)

Yup, rubicon is probably the best initiative I've seen in a long time, fair play to you for putting the time and effort in.

Thank you! It has been a ton of time and quite a bit of money to get started but definately fun! We should see our first grant check soon.

[Ahmed Adly, Marlin Inn DC]

Quote: (Originally Posted by TobyFish)

I take it you've never been to Telford then?

Funny
But seriously, what on earth are these "shit happens" explanations all about?

Poor excuse of a theory by people who know nothing!