X-Message-Number: 2195
Date: 02 May 93 00:36:58 EDT
From: Mike Darwin <>
Subject: LOX Accumulation

From: Mike Darwin
To: Bob Ettinger, All
Re: LOX accumulation
Date: 1 May, 1993

    I would appreciate it if Kevin would be kind enough to relay these
comments to Bob Ettinger ASAP.  

	With my well deserved reputation for thinking the worst and then
believing it, I wish to take credit for being the first (to my knowledge)
to think of the LOX accumulation problem.  I first raised this issue with
Jerry Leaf and Hugh Hixon over a decade ago.  As it turns out, it may be
more of a problem than we all bargained for.  The problem isn't just with
the trace impurities of LOX in the LN2 but rather is compounded by air
being injected into the LN2 via fill tubing and lines, and air mixing in
with vapor when neck tube plugs are removed.  For this reason Alcor went
to nitrogen gas purges of LN2 lines before filling some time ago, and
began capping the open-mouthed neuro dewars with a cover apparatus during
filling (do you at Alcor still do this?).

	About a decade ago Hugh Hixon and I decided to find out exactly
how bad the problem was.  We used an LR-40 patient dewar which had been
in service for two years.  A liquid sample was taken and allowed to
return to gas in a large capacity, heavy duty, toy baloon.  The O2
content was then evaluated with Cryovita's Radiometer blood gas equipment. 
The concentration was in the vicinity of 2% as I recall.  Hugh Hixon has
the notebooks and so could probably give exact details of the experiment.
Also, I think it was written up in CRYONICS at the time.  The control
experiment using fresh LN2 from the supplier showed virtually no
dissolved 02.  We did not look for stratification of LOX in the LN2 and I
doubt whether this would happen since:  1) stratification will be slow,
2) the liquid gets stirred up during refils, and 3) things are pretty
fizzy in there between fills (little known fact: it is NOT quiet inside
dewars, they sound like an opened can of soda, very soft fizzing
sound....).

	Now as to the significance of all this.  The short answer is: I
don't know.  The longer answer is that fire hazards are the LEAST of our
worries.  Oxygen is ACTIVE even at those temperatures.  Indeed, high
carbon steel cannot be used to store LOX since it will be degraded over
time and is a potential combustion hazard.  This is why LOX dewars are
made of stainless steel.  Biological material is not stored in LOX
because LOX damages it.  Years ago there were a couple of researchers
named Salisbury and Graves who claimed that metabolism was going in their
LN2 stored samples.  Most certainly metabolism was not going on, but,
once I learned how they operated, it became clear that LOX contamination
might have been a factor.

	Bob's feelings of reassurance about other operations not
encountering this problem may be misplaced for the following reasons:

1) Very few operations store cells or tissues for prolonged periods of
time (i.e., decades or longer).

2) Even fewer operations store samples in liquid.  Indeed, almost all
semen, tissue culture, embryo, and other cell banking operations I'm aware
of use vapor.  They actively avoid immersion storage in LN2 because it
leaks into vials and causes them to explode.  In fact, at Alcor I
abandoned LN2 storage of archival lab and tissue samples for just this
reason.  There is now an entire MVE A-8000 dewar full of samples being
stored in VAPOR.

3) Some investigators (a few) have reported deterioration in samples
stored in LN2 for a long period of time.  This has always disturbed me
and I have long wondered if LOX could be the culprit.

4) Virtually all labs that store cell and tissue samples protect them from
contact with LN2 and thus slow down the entry of any LOX into the sample. 
Until recently, glass was THE most commonly used vessel material.  Glass
is pretty good at excluding 02.  Even today, to the best of my knowledge,
virtually all sperm and embryos are still stored in glass straws.  Perhaps
Steve Bridge could check with his father on this matter since his father
has long been involved in semen/embryo freezing.
 
5) Suspension patients are in direct contact with the liquid.  If
stratification occurs the PATIENT'S HEAD will be exposed to the HIGHEST
LOX concentration.  Further, in patients with cracks or burr holes and gas
space due to shrinkage of the brain from glycerolization, liquid (and
LOX) may be seeping into the tissue and into the brain along fracture
planes.  Certainly neuro patients who experience CNS dehydration have a
well of LN2 and/or LOX surrounding their brains.  I'll bet liquid seeps
in in the case of whole body patients who do not have burr holes too
(i.e., at CI and TT).

	The take home message here is very simple: the problem of LOX is
potentially serious.  Alcor has taken some steps to inhibit LOX buildup
including NEVER reusing LN2 which is "dirty" (i.e., been used to cool
down patients, been trasferred by buckets, exposed to the air, etc.). 
Also, it is my understanding that when transfer of patients becomes
necessary in a dewar that has been running for a long time the LN2 is
discarded.

	Finally, Hugh Hixon had (over a decade ago!) come up with a novel
and ingenious scheme to deal with this problem, however I don't believe he
ever got round to doing any work to test to out.  How about Hugh?

	Also, we have excellent and very sensitive blood gas equipment
which can also run expired air or atmospheric gases.  I would be more than
willing to work with Alcor to get some numbers on current LOX levels in
various dewars.  Perhaps we could all cooperate (CI, BPI, and ALCOR) and
generate some data.  I would be happy to write up a draft version of the
paper which then could be submitted for publication at some mutually
agreed place.  This is an example of a problem which, while of special
concern to cryonicists, may have broad utility and implications for others
in the "straight" scientific community.

	Finally, finally, my apologies for error ridden text: Paul Wakfer
is away (he normally handles E-mail) and I am using an unfamilar program
to do E-mail which does not have spell-check capability and which makes
editing VERY difficult.

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