X-Message-Number: 33380
From:
Date: Mon, 28 Feb 2011 02:46:08 EST
Subject: Melody Maxim's Distorted Reality 15
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Mke Darwin Mike Darwin
(Login mgdarwin)
Veteran Member
Judge for Yourselves - Part 3 February 3 2009, 11:40 PM
Darwin-Maxcim Correspondence on the CI_Sci_ Forum:
In a message dated 11/20/2008 9:18:31 A.M. Pacific Standard Time,
writes:
I originally wasn't going to respond to Mike's post, because I'm really
just sick and tired of butting heads with non-professionals, in regard to
perfusion, in cryonics. However, I don't think it's productive for the cryonics
community to have Mike Darwin come here making certain (perhaps misguided)
assumptions, and criticizing CI for consulting with a medical
professional, as it is only likely to reinforce the negative attitude that
prevails in
conventional medicine in regard to cryonics, and vice versa.
MIKE DARWINS RESPONSE:
Melody,
I have never criticized any cryonics organization for consulting with
medical or other professionals. In fact, on this list-serve I recommended (some
months ago) that CI contact the AMSECT (American Society of Extracorporeal
Perfusionists) chapter in the Detroit metro area to see if there were
perfusionists interested in working with CI and learning what was required to be
of material assistance in cryonics. I have also offered to put CI in touch
with intensivists and others in medicine that might provide advice and
assistance.
The only negative attitude I know of in cryonics towards medicine is that
of Charles Platt and, in a different way, Bob Ettinger. As I understand it
Bob sees much of medicine as it has been applied to cryonics as gilding the
lily, superfluous, or not worth the cost, or not affordable. If I have any
of this wrong (vis a vis Bobs position) Im sure hell correct me.
You write:
I find it somewhat confusing that Mike recognizes the need for someone
with a "working knowledge of perfusion at Board Certification level - at a
bare minimum," and then acts like such a person is too ignorant to participate
in developing perfusion protocols for cryonics. With all due respect, (and
recognizing that Mike Darwin may know a lot more about medicine, in
general, than I do), I think his knowledge regarding clinical perfusion, and
perfusion equipment, (especially recent developments in perfusion equipment),
is
somewhat limited.
Now, I am puzzled! I have, at least to my knowledge, never had any
exchanges or communications with you beyond a very brief (3-5 min) chat on the
phone when you were employed at SA; Charles put you on the phone with me and we
exchanged some pleasantries. Beyond that, I don't believe you have
communicated with me.
As to my current state of knowledge in terms of hardware and consumables;
I would hazard I'm fairly current. I have e-subscriptions to just about
every perfusion/extracorporeal medicine journal, and I read them including the
adverts. I also count a number of working clinical perfusionists as friends
and colleagues, and I visit centers of cardiovascular surgical and
perfusion excellence all over the world; I just spent time at the premier
institute for cardiovascular surgery in Russia in Moscow. I also read a great
deal
of the primary literature on cutting edge developments in extracorporeal
medicine; I have a longstanding interest in LVAD (left Ventricular assist
Device), TAH (Total Artificial Heart) and bioartificial organ technology. I am
a device nut and have a reputation as a medical technophile. I introduced
the Novametrix CO2SMO into cryonics (sadly no one knew how to use it
properly) and have tried to introduce cerebral function monitoring (onto 15
years
now; since Aspect first started its clinical development of the BIS
monitor) into Transport operations, to no avail.
I pumped some of the first centrifugals and I pumped the very first
pseudo-membrane oxygenators (the horrible Travenols) as well as the first
successful hollow fiber membrane (Bentley). I started research perfusion when
Pemco discs were still in use a (I own both a pediatric and adult disc
oxygenator and I still know how to disassemble, clean and Siliclad them ). Other
than Charles Platt, you are the only person I know who has ever accused me of
not being enthralled with, and knowledgeable about the very latest in
perfusion or medical hardware (or related technology). I'm not sure my passion
in this area is a good thing, but nevertheless, it is very real.
So, again, I'm puzzled by your remarks. I hope you are not mistaking the
madness you saw at SA during your tenure there in any way for my
work-product or advice. In fact, my advice to SA, in almost every respect, was
not
followed. To name just a few areas/items related to CPB: use of the wrong size
arterial pumps, a jury-rigged high-low level sensor for the venous
reservoir which was made of corrodible metals rather than using highly reliable
and physiologically compatible off-the-shelf integrated level detection and
marco/micro-bubble detection system equipped with pump shut off and line
clamp features, failure to use Biomedicus flat wire cannula for femoral venous
return, failure to use gravity assisted drainage... I could go on for
pages...and did. I recently totted up the raw pages of correspondence from me
to
SA and it was over 900 pages long.
You continue:
I came to this conclusion a long time ago, after reviewing many of Mike's
documents about perfusion, and having had a series of exhanges with him,
regarding perfusion equipment, when I first began working with SA.
Again, I have no record of any exchanges with you and I have published
nothing related to perfusion vis a vis cryonics in at least a decade. About
the only things I can think of you that you may have seen from me were my
advice to SA against Charles ideas of:
* using centrifugal pumps (in the field or for CPA perfusion),
*vacuum assisted drainage in the field (in unskilled hands)
*and a moderately strong recommendation against hard-shell reservoirs;
again for in-field use in unskilled hands.
SA may have followed my advice about centrifugal pumps, but certainly didn'
t with respect to hard-shell reservoirs or level/pressure/bubble alarms;
at least not until long after I had no further input, if then.
Interestingly, SA became fixated on vacuum assisted drainage for a truly
amazing reason which had nothing to do with prior (competent) experience
with either in-field TBW or extended duration extracorporeal support of
cryonics patients at ~4-6 deg C. This is the story, written for another person
(non-perfusionist; an engineer) at another time:
I was in Peacehaven (UK) staying with Alan & Sylvia Sinclair circa 2003. I
picked up a copy of The Immortalist from their coffee table and on the
cover was the Mobile Advanced life Support System (MALSS: the MALSS was the
forerunner of the MARC a la Alcor) that Saul Kent had purchased from me when
Kryos folded. It had been modified for operator convenience such that the
venous reservoir was at eye level! This will probably mean nothing to you for
the moment (long explanation to follow), but the practical effect is
devastating. The blood returning to the heart from the body is conducted
through
two very large diameter tubes called the superior and inferior vena cava
(SVC & IVC). The SVC drains the head and upper trunk and the IVC the lower
body. Each is about 25 mm in diameter under resting conditions and they
easily distend under pressure. Normal central venous pressure (CVP) is about 5
torr, and anything above 15 torr causes rapid development of (interstitial)
edema. Above 20-30 torr and you blow the pulmonary alveolar capillary
tight junctions and the lungs not only flood with fluid; fluid will start
pouring out the ET tube inexorably! Nothing you can do will fix this; it is an
irreversible injury which, at very least, is going to make CPA perfusion
(whole body) very difficult because perfusate will escape the circuit from the
lungs at an enormous rate, even under low flow and low pressure conditions
and this perfusate cannot be returned to the blood circuit via cardiotomy
suction as would the case with capillary ooze from transacted small caliber
vessels in the chest.
This issue of tolerable CVP is relevant because flow through the cavae
obey Poiseuilles Law. In laminar fluid flow through a tube or pipe frictional
(viscosity) energy losses occur and these cause a pressure drop along the
length of the pipe as a function of the pipe size, the type of fluid, and
the mean flow velocity or flow rate.
The central formula in the laminar flow model is the Poiseuille equation:
R = (8hL)/pr4.
or Poiseuille law:
Q = (pDPr4)/(8hL),
where P = pressure, n = mean flow velocity, Q = volumetric flow rate, L =
tube length, h = fluid viscosity, and r = tube radius.
The underlying assumption of laminar flow is the condition of uniform
viscosity across the diameter of the tube; each fluid molecule within the tube
is exerting a similar force against each adjacent molecule towards the
periphery. This means that fluid adjacent to the conduit wall is motionless (no
= 0), maximum fluid velocity (nmax) is in the center of the conduit, and
fluid velocity is related to distance from the center (ni) by a parabolic
function. Resistive losses (pressure drops) linearly are related to flow rate
and flow resistance. While flow resistance linearly relates to conduit
length, it is inversely related to the fourth power of the radius (or diameter
of the tube or pipe). For example, a 1-cmdiameter tube has 16 times the
flow resistance of a 2-cmdiameter tube of the same length and carrying the
same fluid. Stated another way, 16 tubes of 1-cm diameter are needed to handle
the same fluid flow at the same pressure as a single 2-cmdiameter tube.
So, when you put someone on femoral-femoral bypass (CPB) in the field you are
forcing ALL the flow that would normally go through TWO tubes each of
which has a nominal diameter of 25 mm (=50 mm combined) through one tube with
an absolute diameter of 12.5 mm! If you do the math you will see that this
will result in a large and physiologically unacceptable increase in
pressure. This difficulty is overcome only by the expedient of gravity-assisted
drainage. You have to put the patient at least 30 cm above the venous
reservoir and be certain to never allow the blood/perfusate in the venous line
to
become air-locked.
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