X-Message-Number: 16277
Date: Sun, 13 May 2001 21:37:11 EDT
Subject: KRYOS NEWS # 6



By Mike Darwin


One "luxury" cryopatients have is that we know they are going to die soon. 
While this state of affairs is normally hardly an advantage, in the setting 
of cryoTransport it can be of enormous benefit. A second somewhat less 
ambiguous luxury they enjoy is that once they become cryopatients they are 
legally and medically dead and thus outside the reach of the vast and killing 
burden of government regulation. In particular, they are free of control by 
those statues that prevent the use of non-government approved medical 
devices, drugs and techniques. This means that US Food and Drug 
Administration (FDA) approval is not necessary before a promising therapy is 
applied to cryopatients after legal death is properly pronounced.


In the mid 1980s I began researching ways to improve closed chest CPS for 
cryopatients. I was then President of the Alcor Life Extension Foundation. My 
colleague Jerry Leaf concentrated on rapid application of cardiopulmonary 
bypass while I focused on improving cryoTransport from the time prior to 
legal death was pronounced to the point bypass could be established. I 
experimented with most of the then novel techniques for CPR including SCV-CPR 
and all of the others I've mentioned above with the exception of "vest" CPR. 
Only one of these new modalities proved a real improvement in the cryonics 
setting: High Impulse CPS. HI-CPS markedly improved cardiac output -- for a 

HI-CPR consists of delivering a very high acceleration downstroke during the 
compression phase of CPS. If the waveform, or the shape of the force of a 
HI-CPR compression is displayed graphically it is almost square. Delivery of 
this kind of abrupt and sustained energy to the chest wall results in the 
heart emptying itself of blood at a fairly high velocity. Traditional CPS 
uses a saw-toothed wave that gives comparatively slow emptying of blood from 
the ventricles of the heart. Because these pumping chambers empty so slowly 
compared to the situation in a spontaneously beating heart, the mitral valve 
does not snap shut. The valves in the heart are not ball valves, but rather 
have leaflets or flaps that close properly only if the flow is vigorous. If 
it is too slow or not sustained enough, the valves do not completely close 
and there is backwards flow, or regurgitation. HI-CPR went a long way towards 
solving this problem.

Its major limitations were that just like conventional CPS it results in very 
high pressure inside the chest during compression (this causes lung edema). 
Also, just as is the case with regular CPS the chest soon loses its natural 
recoil or elasticity and becomes flat. The medical term for this is flail 
chest. While this is not the only reason for the problem I'm about to 
describe, flail chest is a major contributing factor. In order to send blood 
out to the body when it contracts the heart must also be supplied with blood 
returning from the body. A pump cannot pump if it has no supply. The 
efficiency of the heart, unlike some kinds of pumps, is determined by the 
amount of fluid it has flowing into it before it contracts; in other words 
how full the pumping chambers are. This is called preload and it is primarily 
determined by the amount of venous blood flowing back towards the heart.

In a healthy human there are many factors at work to insure that adequate 
preload exists. One common cause of inadequate preload is depleted vascular 
volume: not having enough fluid in the circulatory system. This is usually as 
a result of dehydration, bleeding, or shock. In the case of shock the cause 
of inadequate circulating volume is altered capillary permeability which has 
allowed massive amounts of fluid to leak from the circulatory system into the 
tissues. These causes of inadequate preload can often be transiently 
corrected in the cryopatient by the rapid administration of fluids. However, 
the other mechanisms which cause blood return to the heart from the body 
which fail during CPS are not so easily overcome.


In the 1992 a bizarre case was reported in both the lay press and the medical 
literature where a woman successfully resuscitated her husband from cardiac 
arrest using a toilet plunger {Cohen, 1992 #5160}.  T. J.  Cohen and his 
colleagues investigated the mechanics of this new kind of CPR, christened it 
Active Compression-Decompression CPR (ACD-CPR) and developed a prototype 
device to test it on both animals and humans. The device was ultimately 
brought to widespread clinical application outside the United States in the 
form of the Ambu Cardiopump: a silicone rubber suction cup with a rigid 
plastic handle to allow the operator to both compress the chest and pull upon 
the chest wall after each compression with the suction cup. The handle has a 
compression and decompression indicator built into it to guide the operator 
in the use of the proper technique.

The principle on which ACD-CPR is thought to work is that of increasing 
preload. When the suction cup of the device is pulled up after each 
compression the pressure inside the chest becomes transiently negative 
causing the chest to act as a suction chamber to draw venous blood from the 
body into the right heart in preparation for pumping through the lungs to the 
left heart during the next downstroke. ACD-CPR has been shown to improve 
blood flow to both the brain and the heart and to increase survival in 
in-hospital cardiac arrest patients. It overcomes the problem of flail chest 
by simulating and even improving upon the elastic recoil of the healthy chest 
by pulling up on it with 18 to 20 kg of force after each downstroke of CPR. 
{Rabl, 1997 #45}. 


In 1996 I developed a pneumatically powered CPR device which combined ACD-CPR 
with high impulse CPR and tested this on 7 human cadavers beginning within 
<10 minutes of cardiac arrest. Combining these two modalities resulted in a 
tripling of mean arterial pressure (MAP) from ~30 mmHg to 90 mmHg and an 
increase in end-tidal CO2 (EtCO2) from ~2% to 5%, as compared to when the 
same subjects were evaluated using conventional CPR. The nice thing about 
this study was that each subject served as his/her own control and we started 
with conventional closed chest CPR. Equally important, the length of time an 
adequate MAP and EtCO2 could be maintained was increased from an average of 
11 minutes to an average of 19 minutes {Darwin, 1996 #4196}.
This kind of CPS requires a machine to deliver. However, in most cases where 
advance preparation is possible machine delivered CPS is used. Furthermore, 
all cryonics organizations have these kinds of devices. The prototype 
HI-ACD-CPS device was built for BioPreservation by Michigan Instruments, Inc. 
in 1994. It has been used on one cryopatient since that time and was able to 
maintain cerebral perfusion for 55 minutes after cardiac arrest.


During the course of research to improve resuscitation for cryopatients it 
became apparent that one of the weaknesses of ACD-CPR was that the negative 
intrathoracic pressure that is so desirable for improved preload and thus 
improved cardiac output was being compromised. The reason was that each 
decompression upstroke resulted in air rushing into the patient's lungs. This 
can be an advantage in that each cycle of compression and decompression 
constitutes a ventilation. If CPS is being performed by hand with a 
Cardiopump or similar device this is a real advantage as it makes the job of 
providing CPS easier and less labor intensive. However, for prolonged CPS 
there is a tendency for these very frequent ventilations to cause an 
excessive amount of carbon dioxide (CO2) to be washed out of the patient's 
blood and tissues. While CO2 is a waste product which does need to be 
eliminated via the lungs, if too much is removed circulation to the brain is 
compromised; very low blood levels of CO2 cause brain blood vessels to become 
constricted. In fact, this problem can be so serious that in people who are 
hyperventilating they actually lose consciousness from cerebral vasospasm. 
That's why hyperventilating people pass out; they suffer transient global 
cerebral ischemia!

In addition, the inrush of air on each upstroke during ACD-CPS reduces the 
amount of suction inside the chest that is vital for improving venous return 
to the heart. An obvious solution to this problem is to interpose a valve 
between the patient's airway and the rest of the breathing circuit. The valve 
would remain closed except during a deliberately interposed inhalation and 
exhalation every 3rd to 5th breath. In animals this technique dramatically 
improved preload and increased cardiac output to above basal conditions 
before cardiac arrest.

A simple manual version of this valve consists of a normally closed 
squeeze-clamp which is placed on a piece of silicone rubber tubing connecting 
the patient's endotracheal tube, mask, etc., to the bag valve respirator or 
the ventilator on the mechanical HI-ACD CPS device (Thumper). To use it the 
operator simply squeezes the clamp every 5th compression to open the valve, 
gives a ventilation (or allows the machine to) and then closes it after the 
next compression (the end of exhalation). I gave one of these assemblies to a 
leading cryonics organization approximately two years ago and explained the 
simplicity of the device, its principle of operation and gave them any anyone 
else who wanted to use it permission to do so. To my knowledge this advance 
has not been used. Perhaps it was because the rationale for its use and the 
advantages were not made clear enough.

Combining these three modalities: HI-CPS, ACD-CPS, and airway closure during 
chest decompressions can yield cardiac outputs greater than the resting 
weight adjusted baseline in cryopatients who are adequately hydrated and who 
have good vascular tone. This means that for first time CPS as well as CPR 
could really work -- and work for up to an hour or longer. Kryos will be 
using all three of the modalities and we currently have three CPS machines 
capable of delivering them.

We think that's worth telling people about. And we think its worth the extra 
money we've spent to make it possible. 


(References are available upon request. If you have questions or comments 
please feel free to contact Mike Darwin at )

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