From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: rec.martial-arts,misc.fitness.weights,sci.med
Subject: Re: Hyperventilation before a burst of metabolism
Date: Sat, 18 May 2002 15:45:19 -0700
Message-ID: <ac6lje$v8d$1@nntp9.atl.mindspring.net>

Carey Gregory wrote in message ...
>"Richard Cavell" <richardcavell@mail.com> wrote:
>
>>This thought occurred to me today:
>>
>>During a burst of energy (such as a fight), most people will use up their
>>oxygen reserves pretty quickly.  They then run on anaerobic metabolism.
>>Arterial pO2 can be artificially raised by breathing oxygen concentrations
>>that are higher than that found in air (as in a paramedic supplying oxygen
>>by mask), or by hyperventilation.
>>
>>It occurs to me that oxygen therapy before a burst of metabolism could well
>>delay the switch to anaerobic metabolism, and delay an oxygen debt.  Has
>>anyone tried this?
>>
>>Surely I'm not the first person to think of this.  So why don't Olympic
>>swimmers walk out to the blocks with scuba tanks attached to their faces?
>
>Since someone else has already pointed out that scuba tanks are filled
>with air, not oxygen, I'll merely add that the primary effect of
>hyperventilating is to blow off CO2.  It doesn't raise O2 levels
>significantly.   There's not much a normal, healthy person can do to
>significantly increase their O2 saturation.  Even breathing pure O2
>has a minimal effect.


That's true when resting, but it may not be true if you've got a severe
V'/Q' mismatch. Also, you can always raise your SpO2 a little with pure O2
breathing, as even normal lungs have bit of "physiologic" shunt. At sea
level you'll see you SpO2 go from 94% or so in a young person to 99.

If you've hit your anaerobic threshold it can be for a number of reasons,
and one of them can be that you've hit O2 delivery limits due to inability
to let your venous sats (which you never see with a pulse oxymeter) fall any
further and still extract O2. You can up  that a bit by O2 breathing to
slightly increase your arterial content, and thus delivery, even if your
arterial Sats are good on air and your shunt is no worse than normal. You
don't affect it much, but 5% can be felt. You can see this effect on
endurance sports at even medium altitudes (like 4000 feet) even though these
aren't enough to affect resting SpO2 much in a healthy person.

BTW, if you'll pardon the personal subjective observation-- scuba tanks
aren't always filled with air, even for shallow sport diving. In fact I
typically dive EAN ("nitrox") when I can get it (which is most of the
time), and that's anything from 32 to 40% oxygen (this helps a bit on
nitrogen loading so you can stay at moderate depths like 70 ft for longer,
without needing decompression stops).  It happens not untypically that after
a dive I have to do heavy ocean swimming against current or through kelp
beds to get back to a dive boat, and I can tell you that it certainly feels
easier to do breathing 40% O2 from my reg and tank, than it does air through
a snorkel. So much that I've given up even taking a snorkel.  And this is at
sea level (exactly!) where I'm sure my sats are fine on air.  Of course, the
endurance difference is subjective and certainly not double blind.  Still, I
believe I can tell the difference between air and nitrox on surface swims.
(Divers typically surface with enough reserve gas for half an hour of
surface swimming). I once did a shallow dive on a tank of 50% oxygen which
I'd gotten by mistake from boat O2 fill error.  Swimming back after that
one, I felt like Mark Spitz. It was only later that I put two and two
together.

For the Olympics there's no way anything you could put in a 40 lb pressure
tank would increase an elite athlete's swimming capability enough to
compensate for that much extra weight and drag-- even if it was legal under
Olympic rules, which I can hardly imagine it would be.

SBH

--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.

From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: rec.martial-arts,misc.fitness.weights,sci.med
Subject: Re: Hyperventilation before a burst of metabolism
Date: Sat, 18 May 2002 17:04:30 -0700
Message-ID: <ac6q7s$2ap$1@slb3.atl.mindspring.net>

Carey Gregory wrote in message
<59qdeush1pmm8cdb7p86for9b39bs9dpbc@4ax.com>...
>"Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> wrote:
>
>>That's true when resting, but it may not be true if you've got a severe
>>V'/Q' mismatch.
>
>And how many "normal, healthy" people do you suppose have such a
>severe mismatch?   ;-)


That was phrased badly. Even if you're healthy and young you can go from 94
to 99% at rest on O2. And on exersize you may run less than 94% since that
normal shunt will be giving you badly desaturated venous blood (50% or even
less). Finally, the normal physiologic shunt and your A-a gradient all
increase with age. So those "master's class" olympians will get more from
the enriched O2 than the younger athletes.

Gee, now that I think about it, I got so much kick from 50% nitrox that I
ought to do some oxymetry on myself after heavy exercise to see if *I'm*
desaturating on exertion   ;(   I know I'm fine at rest, but maybe I have
some PAH or a small PE or something nasty that I haven't picked up. I really
could be in much better shape for my age-- it's not like I routinely run
marathons-- so I have lots of room to hide a little pathology.

SBH

--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.

From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: sci.med
Subject: Re: Hyperventilation before a burst of metabolism
Date: Mon, 20 May 2002 17:04:32 -0700
Message-ID: <acc2vu$84m$1@slb0.atl.mindspring.net>

Carey Gregory wrote in message ...>[headers trimmed]
>
>"Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com> wrote:
>
>>Deco tanks are filled with pure O2 for open-circuit tech divers who need to
>>do long decompressions. These guys stay for hours sometimes, stuck at 20
>>feet, breathing pure O2 with occasional "air breaks" which helps the
>>pulmonary toxicity.
>
>What's the purpose of the pure O2?


Merely to provide gas which has no inert gas component. This maximizes the
gradient of partial pressure (pp) of inert gas disolved in tissues, with
respect to the pp of inert gas in the blood plasma/lungs.  That gradient
determines how fast dissolved inert gas will move from "slow" tissues to
blood/lungs, and be eliminated. The partial pressure of oxygen in the
tissues does not act to form bubbles, even when total ambient pressure is
much lower than pO2, because oxygen disappears from solution (and presumably
from bubbles) from metabolism so quickly that it can't build up. By
contrast, inert gases like helium and nitrogen are at risk for bubble
formation and fizz whenever you drop ambient pressure to less than about 1.3
atm lower than the total pp of all inert gases dissolved in the "slow" body
compartment at worst risk (say, your spinal cord). In other words, since
it's (tissue inert gas pp minus lung inert gas pp) that drives the process
that decompresses you, but it's a max limit on (tissue inert pp minus total
lung gas pressure/ambient pressure) that sets the "bends-risk" or DCI limit,
you obviously want to keep the lung partial pressure of O2 as high as you
can.

Alas, that also is subject to a constraint, since there's a limit to how
long you can breathe pure O2 at high pressure, without ox-tox and seizure
risk. It took J.S. Haldane in historic experiments only a few minutes to go
into full seizure, at 7 atm O2 (he was in a pressure chamber so he didn't
drown, but a diver well might). You can do a few hours at 1.45 atm O2
absolute, and on decompression people generally go to 1.6, which corresponds
with pure O2 breathing at around 15 to 20 feet depth (33 ft = 1 atm in the
ocean).  Deeper stops, however, cannot be done on oxygen, and have to be
done on a mix which is less than 100% O2, but they're generally short and
decompression divers generally do all of them on the same nitrox mix once
they get to a depth which will keep their pO2 < 1.5.  It's that last 16 ft
rise from 1.5 atm to 1 atm which exposes a diver to most of the
decompression risk, and that's why the most decompression time is always
spent relatively shallow, at this depth. So the techie divers stay there
until their calculations show their risky body compartments are down to no
more than 1.3 atm of helium+nitrogen. That happens the fastest when they are
breathing pure O2. Not even all tech divers use the stuff, however, since it
means an extra dedicated tank full of a gas that can ONLY be used at depths
less than 20 feet, and is very dangerous below that. So a much more common
deco mix is 50% nitrox, which gives something that can be used down to 70
feet or so, and even deeper in emergencies.

Another practical cutoff in scuba occurs for mixes which contain no more
than 2200 psi O2 absolute in the tank, which corresponds to 2200/3500 = 63%
02 in the standard high pressure steel 3500 psi scuba tank (we Americans
only go to 3500-- in Europe they typically run to 4400 psi or 300 bar).  The
American Compressed Gas Association does not certify a lot of fittings and
components for oxygen at pressures over 2200 psi absolute partial pressure
(what you see in your average medical H cylinder of O2) and neither do most
scuba shops. So 60% nitrox is all you can get, most places.

Tech divers who use 100% O2 are (needless to say) extraordinarily careful
with it. Breathing your 50% nitrox by mistake at 100 ft while make an ascent
won't do you in, but making a mistake and breathing your 100% O2 at that
depth would kill most people by seizure/drowning, in a few minutes.

SBH

--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.