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One explanation of this was given to me by a friend who is a blood
pathologist as well as being a gas diver. He says that high PPO2s tend to
cause vascular dilation in the brain, which increases the delivery of
nitrogen to those tissues, resulting in increased narcosis. I'm not a
physiologist, so I'm just passing this one along.
I do note that this explanation would imply that increased O2 in a mix would
increase narcosis for a short dive (or early in a long dive) since the O2
would increase the rate of delivery of N2 to brain tissue. Eventually the
PPN2 in the brain would equilibrate to the same level for a given depth and
amount of N2 in mix regardless of O2, so for a long dive the narcosis level
shouldn't be affected by the level of O2.
John
_______________________________________________________________________________
From: Richard Pyle on Wed, Jun 29, 1994 4:49 PM
Subject: Re: Oxygen narcosis (?)
To: JOHNCREA@de*.co*
Cc: techdiver@opal.com
On Wed, 29 Jun 1994 JOHNCREA@de*.co* wrote:
> Rich,
>
> Obviously, considering that oxygen should (based on lipid solubility)
> be about 2x as narcotic as a comparable partial pressure of nitrogen.
>
> However, the research done (1 study) suggested that oxygen was about
> equi-potent with nitrogen (maybe due to the metabolic pathway and
> consumption of oxygen at the cellular level).
>
> John
As has been discussed before, oxygen seems to have sort of a synergistic
effect with nitrogen in causing narcosis (i.e., pure O2 at super-high partial
pressures doesn't seem to have much of a narcotic effect). I suspect,
therefore, that oxygen and nitrogen will not be equi-potent at all ratios
and at all depths. My experience (admittedly anecdotal) tells me that at
about 200', if you increase the oxygen:nitrogen ratio, narcosis is
exacerbated. I hypothesize that under similar conditions, if I decrease
that ratio (i.e., more nitrogen), narcosis may similarly decrease.
This makes sense from a lipid-solubility standpoint if you view the amount of
available oxygen in the tissues as being a certain amount ABOVE what is
being metabolized: At relatively low inspired PPO2's, a larger proportion
of total dissolved O2 is metabolized when compared with relatively high
inspired PPO2's.
A metaphor might be a combustion reaction: nitrogen being the analog of
fuel, and oxygen serving the same analagous function as oxidizer: Oxygen
alone is non-flammable (or, in our case, non-narcotic); combine it with a
fuel and you can have a combustion (combine it with nitrogen and you can
have narcosis). You can limit or increase the vigor of a burning flame by
limiting or increasing the availability of oxygen. I'm suggesting that,
perhaps, at the sort of depths we're talking about (150-250 feet), the
abundance of oxygen in the breathing mix might govern the extent of
narcosis severity (within certain parameters). Now bear in mind, I
realize there is no similarirty between a combustion reaction and the
physiology of narcosis at the molecular level: I'm just using it as a
metaphor.
I'll let you know what the results of my little informal study turn out to
be (I'll probably try it early next year).
Aloha,
Rich
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Date: Wed, 29 Jun 1994 10:06:49 +22305714 (HST)
From: Richard Pyle <deepreef@bi*.bi*.ha*.or*>
Subject: Re: Oxygen narcosis (?)
To: JOHNCREA@de*.co*
Cc: techdiver@opal.com
In-Reply-To: <01HE3SI32RO29AMZTW@de*.co*>
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