David J. Chalmers on the Singularity, mind uploading and cryonics

16. September 2010 · Comments Off · Categories: Cryonics, Neuroscience, Science · Tags: , , , ,

If I would make an argument in favor of mind uploading (or substrate independent minds) it would not be a logical deduction from what we know about neuroscience but from what we don’t know.  As one of the leading philosophers of mind David J. Chalmers has argued in this insightful paper about the Singularity and mind uploading:

Can an upload be conscious? The issue here is complicated by the fact that our understanding of consciousness is so poor. No-one knows just why or how brain processes give rise to consciousness. Neuroscience is gradually discovering various neural correlates of consciousness, but this research program largely takes the existence of consciousness for granted. There is nothing even approaching an orthodox theory of why there is consciousness in the first place. Correspondingly, there is nothing even approaching an orthodox theory of what sorts of systems can be conscious and what systems cannot be….

It is true that we have no idea how a nonbiological system, such as a silicon computational system, could be conscious. But the fact is that we also have no idea how a biological system, such as a neural system, could be conscious. The gap is just as wide in both cases. And we do not know of any principled di differences between biological and nonbiological systems that suggest that the former can be conscious and the latter cannot. In the absence of such principled di differences, I think the default attitude should be that both biological and nonbiological systems can be conscious

One can argue with this derivation of what the “default position” should be, but his more skeptical approach has a degree of modesty in its favor that is often lacking in transhumanist circles.

David J. Chalmers also discusses cryonics in a favorable context:

Cryonic technology off ers the possibility of preserving our brains in a low-temperature state shortly after death, until such time as the technology is available to reactivate the brain or perhaps to upload the information in it. Of course much information may be lost in death, and at the moment, we do not know whether cryonics preserves information sufficient to reactivate or reconstruct anything akin to a functional isomorph of the original. But one can at least hope that after an intelligence explosion, extraordinary technology might be possible here

On his blog he also writes that “for the last couple of weeks I have been in Oxford giving the John Locke Lectures on Constructing the World.  The title is an homage to Rudolf Carnap’s 1928 book Der Logische Aufbau Der Welt. The lectures are based on a book I have been writing for the last couple of years, trying to execute a project that is reminiscent of Carnap’s in certain respects.”

A person who discusses mind uploading in a meaningful context, gives cryonics a fair hearing, and has a work in progress that is inspired by Rudolf Carnap’s The Logical Structure of the World should not be ignored, let alone be ridiculed.

Buddhism and the scientific worldview

15. August 2010 · Comments Off · Categories: Neuroscience, Society · Tags: , , , , ,

On his blog The Life of Man Qua Man on Earth Mark Plus takes a critical look at Buddhism:

Transhumanists who endorse Buddhism tend to annoy me. Buddhism not only has the problems John Horgan points out, but the empirical evidence doesn’t support its fans’ claims about happiness…The developed countries where Buddhism has had the least presence and influence, with the exception of Japan, now report the highest levels of happiness; while the poorer countries with Buddhist cultures report significantly lower levels of happiness…Ironically the legends about the Buddha show that he depended on others’ dukkha for his subsistence and cult building.

Because Buddhism can be more easily adapted to support secular believes and modern science, its popularity among some transhumanists is not surprising. It has been argued that indeterminism in physics and the currents findings of neuroscience about the existence of “the self” have been anticipated by Buddhism. Of course, there are also metaphysical, epistemological, and moral ideas within the Buddhist tradition that are harder to reconcile with modern science. It is challenging to understand why one should make a conscious effort to reconcile Buddhism and contemporary science. We can embrace the findings of  science that are consistent with Buddhism but reject the  metaphysical baggage of Buddhism and many other “isms” as obstacles to a proper scientific conception of the world.

Buddhism is not unique in offering guidance about how to live in an increasingly technological world. Contemporary physics and neuroscience leave little room for the existence of “free will.” Living without free will seems disconcerting to many people (including self-identified atheists) but traditional Calvinists have learned how to cope with such a possibility. Considering the long and diverse history of religion, it stands to reason that some of the concerns expressed in various belief systems still hold relevance for humans today. But none of these belief systems can substitute for the skepticism and moderation that a proper understanding of science brings.

Free will versus determinism as it relates to cryonics

30. July 2010 · Comments Off · Categories: Cryonics, Neuroscience, Science · Tags: , , , , ,

Excerpt from “Ben Best – A Case for Free Will AND Determinism”

Determinism implies materialism — implies that consciousness is material. Cryonics is based on the premise that the preservation of the fine structure of the brain at low temperature will preserve the self — ie, that the self is entirely determined-by and contained-in the physical brain. Determinism would imply that preservation of the material basis of mind/self is theoretically possible. (For an exploration of how the self is encoded in the brain, see my series The Anatomical Basis of Mind. Development of the anatomical argument to explain the functioning of mind is best summarized in Chapter 8, Neurophysiology and Mental Function.)

Defenders of “free will” who say that the self has a spiritual basis independent of the brain often reject cryonics as being unnecessary. There are a few “spiritually” oriented people (like the Fyodorovians) who think that “resurrection of the body” is essential due to an intimate connection between the body and the “soul”, but these are in the minority. The majority of cryonicists do not accept spiritual beliefs, but there are notable exceptions, namely people who regard cryonics as a form of medicine. If cryonics can extend life, it is no more an affront to spiritual belief than other life-extending practices such as exercise and the avoidance of tobacco.

What about anti-determinist materialists who believe in “free will”? Those, like Roger Penrose, who claim that the mind is ultimately rooted in quantum uncertainty might not accept the possibility of biostasis, but Penrose has made no explicit statement about this subject. Penrose writes of the non-computability of mind, but acknowledges that non-predictability does not equate with “free will”.

Predictability is really at the heart of what is required for cryonics. If the mechanical operation of billions of neurons and trillions of synapses result in the phenomena known as the mind, the Self and the Will, then preservation & restoration of this machinery by cryonicists & nanotechnologists is possible in principle. But this also means that human beings are machines whose future actions are, in principle, entirely predictable. The positive side of this is that understanding the machinery in sufficient detail could provide the basis for reconstructing those aspects of the mind (parts of the brain) that were destroyed beyond recognition or repair. The negative side is that many people find it “dehumanizing” to believe that we are nothing but machines.

The proposition that the self/mind has a complete material basis in the mind has practical implications for cryonics, but also raised baffling questions. If it is possible to use a cryopreserved brain as a template for atom-by-atom reconstruction of a new brain, the identity of the person whose brain was cryopreserved would presumably be restored. But if such reconstruction could be done once, there is no reason why it could not be done hundreds of times. Would each reconstruction have the same personal identity (the same self) as the original? (For more detail on this question, see my essay The Duplicates Paradox).

Chemical preservation and cryonics research

22. July 2010 · Comments Off · Categories: Cryonics, Neuroscience, Science · Tags: , , , , ,

In the 2009-4 issue of Alcor’s Cryonics magazine I review the technical and practical feasibility of chemical preservation. One of the most interesting aspects of chemopreservation is that it could play a useful role in the cryopreservation of ischemic patients.

There is accumulating evidence that vitrification agents cannot prevent ice formation in ischemic patients. This raises the question whether some cryonics patients could benefit from chemical fixation prior to transport and cryoprotective perfusion.

Such protocols raise a number of obvious concerns but the question is not so much whether these procedures are inferior to vitrification of non-ischemic patients, but whether fixatives can improve the situation of some ischemic patients compared to the prospect of substantial ice formation, or even straight freezing (cooling without cryoprotection). This is an empirical question which needs to be settled by experimental research.

Chemopreservation: The Good, The Bad and the Ugly

Down with uploading

25. March 2010 · Comments Off · Categories: Cryonics, Neuroscience, Science · Tags: , , , ,

Over the last couple of years, cryonics pioneer Robert Ettinger has been a vocal critic of simplistic defenses of the idea of mind uploading as a survival strategy. He has worked out his reservations in detail in his latest book Youniverse: Toward a Self-Centered Philosophy of Immortalism and Cryonics. In a recent CryoNet message he reiterates some of his basic arguments:

“Identity of indiscernibles” is a  common tenet. Often attributed to Leibniz, one  version is that if two physical objects or systems cannot be distinguished from  each other by any criterion, then they  must be considered the “same” or  identical. First, this assertion actually asserts nothing except a  certain preference in use  of language. It has no consequences. It is also useless because if the question arises, are A and B distinguishable, the answer  is always yes.

It is hard to see how anyone can claim complete certainty  on the topic of mind uploading. Nevertheless, to some of its more dogmatic advocates the case for mind uploading is simply an exercise in deductive reasoning. There are major objections to such an attitude. The most obvious point is general; why should mind uploading be an exception to the rule that we can have no certain knowledge? One might object that absolute certainty is possible in logic. But in that case one would need to defend the thesis that the feasibility of mind uploading (and its associated views about identity) is a purely logical matter and exempt from empirical testing. This is not a credible position.

This does not mean that questions about identity will be easily answered when such technologies are available. For all we know, mind uploading will be technically feasible and the debates about identity continue.  There is a lot of merit to discussions about mind uploading and identity, especially for those interested in cryonics and life extension. But there is also a lot to say for being modest in making bold claims before such technologies have materialized.

Brain preservation

28. January 2010 · Comments Off · Categories: Cryonics, Death, Neuroscience · Tags: , , , , ,

Mind uploading advocate Kenneth Hayworth has launched an interesting website devoted to the science of brain preservation. Of particular interest is his Proposal for a Brain Preservation Technology Prize (PDF). This document includes one of the most comprehensive discussions of chemopreservation as a strategy for personal survival. For example, one of the most common objections to chemopreservation is that fixatives like formaldehyde and glutaraldehyde do a poor job of fixing lipids. In this document, Hayworth reviews a number of papers where a fixative that can stabilize lipids, osmium tetroxide, is perfused (!) through the circulatory system.   For human sized brains such a step would be necessary to avoid the ischemic damage and autolysis that would occur in the case of the time-consuming alternative of diffusion fixation.  He also speculates that such a fixed brain can be perfused with a high viscosity plastic resin for long term preservation.

One of the limitations of this approach, as the author concedes, is that the procedure needs to be started before death. In reality, the situation is even more challenging  than that because the procedure would have to be started before ischemia-induced brain perfusion abnormalities associated with terminal disease and the agonal phase will manifest themselves. This is a problem where “old fashioned” cryonics has a clear advantage. Perfusion impairment may interfere with complete distribution and equilibration of the cryoprotectant in the brain but the unperfused tissues will still be stabilized (although in a damaged form) through low temperatures. In the case of chemical fixation such a “second chance” is absent. This is not just a theoretical problem. Cryonics researchers have become painfully aware of the adverse effects of even the slightest perfusion artifacts on the quality of fixation and the resulting electron micrographs.

As a consequence, this kind of “high quality” chemopreservation can only be a credible alternative for cryonics if the medical establishment would permit the procedure for those who are diagnosed as terminally ill. If the acceptance of cryonics is any guidance, there is little chance that this will happen any time soon.

Chemopreservation has another major obstacle to deal with. As the cryobiologist Brain Wowk has stated on numerous occasions, chemical fixation is a dead end in terms of reversibility with contemporary technologies. This aspect of chemical fixation limits the demonstration of its technical feasibility to a demonstration of ultrastructural preservation.  In the case of cryonics, evidence of excellent ultrastructural preservation has produced little excitement among the scientific establishment and the general public. Linking chemopreservation exclusively to mind uploading may present another obstacle to its acceptance.

In his essay Killed by Bad Philosophy: Why brain preservation followed by mind uploading is a cure for death [PDF] Kenneth Hayworth attempts a defense of mind uploading by identifying the philosophical errors that those who reject the concept, and those who argue that “a copy is not you” in particular, engage in. The author shows little doubt about his position although one might object that the central example that is used to make the case could also be used to  argue against mind uploading. One might even object  that the whole debate involves a pseudo-problem if any kind of empirical observation can be made consistent with the case for and the case against mind uploading.

Aside from these complexities, this is an admirable effort to raises interest in high quality brain fixation. Initial funding for more experimental research should be encouraged.

Revival of cryonics patients literature

10. September 2009 · Comments Off · Categories: Cryonics, Neuroscience, Science · Tags: , , , , , , , ,

There is a growing literature that discusses the technical aspects of revival of cryonics patients. The following list of the published literature was compiled by Ralph Merkle and Robert Freitas and published as an appendix of their article on molecular nanotechnology in Cryonics Magazine 2008-4:

Robert C.W. Ettinger, The Prospect of Immortality, Doubleday, NY, 1964

Jerome B. White, “Viral Induced Repair of Damaged Neurons with Preservation of Long-Term Information Content,” Second Annual Cryonics Conference, Ann Arbor MI, 11 April 1969

Michael G. Darwin, “The Anabolocyte:  A Biological Approach to Repairing Cryoinjury,” Life Extension Magazine (July-August 1977):80-83

Thomas Donaldson, “How Will They Bring Us Back, 200 Years From Now?” The Immortalist 12 (March 1981):5-10

K. Eric Drexler, Engines of Creation:  The Coming Era of Nanotechnology, Anchor Press/Doubleday, New York, 1986, pp. 133-138

Brian Wowk, “Cell Repair Technology,” Cryonics 9(July 1988)

Mike Darwin, “Resuscitation: A Speculative Scenario for Recovery,” Cryonics 9(July 1988):33-37

Thomas Donaldson, “24th Century Medicine,” Analog 108(September 1988):64-80 and Cryonics 9(December 1988)

Ralph C. Merkle, “Molecular Repair of the Brain,” Cryonics 10(October 1989):21-44

Gregory M. Fahy, “Molecular Repair Of The Brain: A Scientific Critique, with a Response from Dr. Merkle,” Cryonics 12(February 1991):8-11 & Cryonics 12(May 1991);  “Appendix B. A ‘Realistic’ Scenario for Nanotechnological Repair of the Frozen Human Brain,” in Brian Wowk, Michael Darwin, eds., Cryonics: Reaching for Tommorow, Alcor Life Extension Foundation, 1991

Ralph C. Merkle, “The Technical Feasibility of Cryonics,” Medical Hypotheses 39(1992):6-16

Ralph C. Merkle, “The Molecular Repair of the Brain,” Cryonics 15(January 1994):16-31 (Part I) & Cryonics 15(April 1994):20-32 (Part II)

Ralph C. Merkle, “Cryonics, Cryptography, and Maximum Likelihood Estimation,” First Extropy Institute Conference, Sunnyvale CA, 1994

Ralph Merkle, “Algorithmic Feasibility of Molecular Repair of the Brain,” Cryonics 16(First Quarter 1995):15-16

Michael V. Soloviev, “SCRAM Reanimation,” Cryonics 17(First Quarter 1996):16-18

Mikhail V. Soloviev, “A Cell Repair Algorithm,” Cryonics 19(First Quarter 1998):22-27

Robert A. Freitas Jr., “Section 10.5 Temperature Effects on Medical Nanorobots,” in Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999, pp. 372-375

Ralph C. Merkle, Robert A. Freitas Jr., “A Cryopreservation Revival Scenario using MNT,” Cryonics 30(Fourth Quarter 2008).

A simple method to resuscitate rats from cold circulatory arrest

12. January 2009 · Comments Off · Categories: Death, Health, Neuroscience, Science · Tags: , , , , ,

This is the eighth entry in a series about resuscitation of non-hibernating rodents from circulatory arrest at ultraprofound hypothermic and high subzero temperatures. In 1982, P.D. Rogers and G.P. Webb published some of their observations (based on previous papers and a Ph.D thesis) after carrying out a classroom demonstration of suspended animation in which they cooled rats and then resuscitated them after 30 minutes at 0 degrees C. The demonstration was performed as a means to stimulate discussion among students regarding the characteristics and diagnosis of death, the effects of hypoxia during cooling, and the limitations of ECG measurements.

Because the “Giaja method” of cooling employed by Andjus and Smith induced hypoxia and hypercapnia, the authors were interested in comparing resuscitation rates in hypoxic vs. non-hypoxic animals. They did so by anesthetizing rats and immersing them (except for limbs, tail, and head) in crushed ice and water to induce ultra-profound hypothermia, as measured by rectal temperatures. During the cooling process, some animals were artificially ventilated until cardiac arrest (respired rats), while others were not (unrespired rats). After 30 minutes of cardiac arrest at temperatures near 0 degrees C, all rats were ventilated during rewarming in a 40 degree C water bath until heartbeat returned and reached 60 beats/min, at which point they were removed from the bath and warming was continued under a 100 W lamp. ECG was recorded throughout.

Rogers found that approximately 90% of respired rats began breathing spontaneously during rewarming and 100% regained heartbeat. On the other hand, less than 10% of unrespired rats recovered spontaneous respiration during rewarming, and when the heart did restart (it often did not), heartbeats were erratic and did not circulate blood due to severe vasodilation assumed to be caused by the combination of hypoxia and hypothermia. Rogers found that he was able to resuscitate 70-90% of unrespired rats by means of abdominal compression (i.e., “abdominal pumping”), but even this method was only successful when the heart restarted.

Though it is easy to assume that hypoxia is the cause of more difficult and less successful resuscitation of unrespired vs. respired rats, Rogers and Webb point out that respired rats may simply be benefiting from the protective effects of hypocapnia on pH changes during hypothermia. They discuss at length the question of “what is the optimal pH in the hypothermic animal,” which remains unanswered.

An interesting phenomenon known as “heart block” was also demonstrated by these experiments. ECG recordings obtained from unrespired rats often showed a QRS complex during rewarming, which most people would assume to indicate that the heart had restarted. However, because ECG is simply a record of electrical activity, this is not always the case:

The observation that a QRS complex occurs in the absence of cardiac output illustrates the limitations of ECG measurements. The ECG is a record of electrical activity within the heart, and any conclusions about mechanical events are extrapolation, though usually with sound theoretical and empirical foundation. In fact, when the chest cavity is opened in unrespired animals with temporarily restarted hearts, it is possible to record QRS complexes in the absence of any apparent heartbeat, i.e., dissociation between excitation and contraction.

Suggestions for further hypothermia experiments in rats include measuring blood pressure during cooling and rewarming, removing blood samples for pH and gas analysis during the experiment, and monitoring electroencephalogram (EEG). Having discovered in previous experiments that unrespired rats suffered from a  collapse in blood pressure during cooling prior to cardiac arrest, while cardiac arrest and blood pressure collapse occurred simultaneously in respired rats, Rogers also wonders whether this pre-arrest collapse can be prevented with vasoactive medications and whether this would improve resuscitation rates in unrespired rats. Answering questions such as these would have far-reaching implications in the treatment of accidental hypothermia in humans.

The method that was used by Rogers et al. to resuscitate rats from ultra-profound hypothermia appears superior in terms of animal welfare and equipments needs. Because hypothermia is not induced by methods that induce hypoxia (as in the experiments of Andjus and Smith), the need for specific warming protocols are greatly lessened.  The use of anesthetics and ventilation during cooling allows the researcher to exclusively focus on the mechanisms of cold circulatory arrest and investigate methods (such as administrations of medications or complete blood substitution) to prolong the period rats can tolerate ultra-profound circulatory arrest and even subzero temperatures.

Robert White on brain death

24. December 2008 · Comments Off · Categories: Cryonics, Death, Neuroscience · Tags: , , ,

Robert J. White is most known, or perhaps most notorious, for his work on primate head transplants. Less known, but more relevant to the practice of human cryopreservation, is his work in cerebral ischemia, hypothermia, and brain preservation. Most of White’s innovative work was published in the 1960s and 1970s. White also published a substantial number of opinion pieces on a variety of topics. One of these topics is brain death.

In an 1972 editorial for the publication Hospital Progress, “The Scientific Limitation of Brain Death,” White notes that:

…we have to acknowledge the probability that eventually all of the major cellular complexes of the human body will be replaceable either by transplanted organs (man or animal) or by sophisticated engineering modules.

As a consequence, the clinical definition of death is shifting from cardiopulmonary criteria to the central nervous system. But unlike other organs,

…this system is not replicatable, representing as it does the repository of the highest functions of man…when this elite cellular system fails it would seem reasonable to assume that what is characteristically ‘human’ is also being lost from the body.

But just as the cardio-respiratory definition of death has evolved and changed with the clinical practice of cardiopulmonary resuscitation,  a similar fate may be in store for the definition of brain death. The clinical use of general anesthesia and hypothermic circulatory arrest, in which the brain can be put “on pause,” emphasize how important the aspect of “irreversibility” is.

As presently defined, the definition of brain death puts much emphasis on brain function upon physical examination. A major limitation of this definition is that it categorically ignores the prospect that brain function could be restored in the future by technologies more advanced than practiced today, provided the material basis of brain function is preserved.

Another challenge is that the science of cryobiology has advanced to such a state where brain slices can be preserved at subzero temperatures and recovered without loss of viability through vitrification. When recovery of organized electrical activity can be demonstrated in vitrified mammalian whole brains, the prevailing definition of brain death will need to be challenged again because it will open the practical possibility to maintain critically ill people in a state of low temperature circulatory arrest without producing one of the indicators of irreversible brain death. Such advances would be an extension of the  experiments Robert White did on isolated hypothermic brains.

As White stresses in the final paragraph of his paper:

…like all biological activity, life and death merge into one another representing a continuum and the neuro-scientist can only in the final analysis determine the point of irreversibility of this highly complex system at which the possibility of organized activity that characterizes human behaviour  has been exceeded.

Promoting cerebral blood flow in cryonics patients

17. October 2008 · Comments Off · Categories: Cryonics, Neuroscience · Tags: , , , , , , ,

It has been shown that perfusability of the brain is significantly compromised after long-term (>5 min) ischemic events (the “no reflow” phenomenon). Improving cerebral blood flow after circulatory arrest is one of the fundamental objectives of human cryopreservation stabilization protocol.  To that end, cryonics organizations administer the resuscitation fluid Dextran-40 and the drug Streptokinase to dilute the blood (and inhibit  red cell aggregation / cold aggulination) and  break up blood clots, thereby improving macro and microvascular circulation. Research by Fischer and Ames, who investigated the effects of perfusion pressure, hemodilution, and anticoagulation (i.e., the use of heparin) on post-ischemic brain perfusion, indicated that hemodilution is the most effective component of the post-ischemic perfusion protocol for enhancing brain perfusability. However, a later study by Lin, et al. (1978) reported significant improvement of cerebral function and blood flow with combined dextran and Streptokinase administration after cardiac arrest in dogs.

In their study, the researchers measured regional cerebral blood flow and cardiac output as well as EEG (i.e., brain wave activity) during five hours of post-resuscitation physiological maintenance following 12-16 minutes of cardiac arrest. Animals were divided into three groups as follows:

Group I:   no treatment

Group II: 1 g/kg dextran 40 in 10% saline following arrest and 10 mg/kg/minute during the five hour maintenance period

Group III: combined therapy of dextran-40 and Streptokinase — same dose of dextran as Group II and 5,000 u/kg rapid infusion and 25 u/kg/minute during the five hour maintenance period

The duration of flat EEG was significantly shorter in Group III animals (20 to 45 minutes with a mean of 28.8 +/- 2.8) than in Groups I (20 to 120 minutes with a mean of 59.5 =/- 10.8) or II (20 to 62 minutes with a mean of 46.9 +/- 4.8) and showed a faster recovery pattern than in Group I (significant difference was reached at three hours). Group II also showed a faster EEG recovery than Group I, reaching significance at five hours.

Cerebral blood flow, particularly in the hippocampus and grey matter (the areas most detrimentally affected by ischemia) in Group III was significantly improved as compared to Group I as early as three hours post-arrest, and was greater than that in Group II (significantly better only in the hippocampus). There was no difference in cardiac output found between the treated and untreated groups. All groups suffered a decrease in cardiac output of nearly 50% of baseline level (measured at 3 and 5 hours post-arrest).

Hematocrit — the proportion of blood volume occupied by red blood cells — was measured in each group and was found to be significantly increased during the post-arrest period in Group I, decreased to 25% of the baseline measurement in Group III (at both 3 and 5 hours post-arrest), and unchanged in Group II.

The authors speculate that “the improvement in cerebral circulation at the microvascular level after infusion of low molecular weight dextran was thought to be 1) related to the rapid increase in plasma volume with resultant lowering of hematocrit and reduction in blood viscosity, 2) a direct effect on the RBC [red blood cell] which increases its negativity and reduces the tendency to cellular aggregation.” They also note that though some doubt had been cast by the Fischer and Ames paper on the hypothesis of vascular endothelial cell swelling as a cause of no reflow, they did observe a higher proportion of smaller diameter capillaries in ischemic brains as compared to controls, and that “if capillary narrowing does play a role in microvascular deterioration, then hemodilution and prevention of cellular aggregates such as occurs with dextran would be beneficial in minimizing poor flow in narrow capillaries.”

Taken together, these findings indicate that combined dextran-40 and Streptokinase therapy improve brain perfusion after cardiac arrest — at least for arrest periods of up to 16 minutes.– supporting the choice for these agents in cryonics. One limitation of this study, however, is that the experiments did not include a group which received only Streptokinase. Including a Streptokinase group would have given more  precise data about the individual effects of the two agents in improving post-ischemic cerebral blood flow. Recent clinical trials with clot busting agents in cardiac arrest have failed and some contemporary authors question the phenomenon of post-arrest blood clotting. Perhaps streptokinase is useful in the treatment of circulatory arrest but its efficacy is dependent upon other blood flow improving interventions such as hemodilution. The case for post-ischemic hemodilution (and interventions to reduce RBC aggregation) is strong but the case for antithrombotic therapy in cryonics (and resusctation medicine) remains to be made.

« Older articles
Newer articles »