In a previous column called “Iatrogenesis and Cryonics” I observed that cryonics is uniquely vulnerable to iatrogenic injury because the objectives of individual cryonics procedures (such as stabilization) are not clearly defined and due to the lack of obvious feedback that a low temperature stabilization procedure entails. This does not mean that cryonics advocates have not thought about how to look at the overall quality of a cryonics case. On the most general level we can evaluate a cryonics case by looking at the degree to which the cryonics stabilization procedure itself adds additional injury to the patient. This is important because critics of cryonics are usually more skeptical about the effects of stabilizing the patient at cryogenic temperatures than about the idea that a person who is considered terminally ill today may not be considered terminally ill in the future. The idea that the cryonics procedure itself does not add additional injury to the patient also ties in with the idea that one of the most important mandates of medicine is to do no harm.

What can a credible cryonics organization do to move its procedures in the direction of reversibility? At the most general level it can reflect this by formally recognizing the goal of developing human cryopreservation technologies that are injury-free. In terms of a research objective, this means that it should aim for human suspended animation. The idea of reversible human cryopreservation is straightforward and easy to communicate. In fact, most laypeople who first hear about cryonics intuitively grasp this point. It also provides a useful benchmark to assess the degree of technological progress at a cryonics organization and evaluate the performance of a cryonics organization in cryopreserving humans.

But how can the concept of reversibility be applied to a cryonics organization that has not yet perfected reversible human cryopreservation? In this case one can still ask how far we can push the goal of reversibility. This raises another challenge. How can we know to what point our procedures are still reversible if we do not actually reverse them? For starters, we can look at the limits of conventional medicine (hypothermic circulatory arrest) and ensure that our procedures conform to the physiological requirements of these procedures. Another (complementary) approach is to define reversibility as maintaining viability of the brain and collect data that will provide us with an answer regarding how well we have achieved this objective.

As I write this, our understanding is that, under ideal circumstances, we can keep the brain viable up to at least the early stages of cryoprotective perfusion (which is conducted around 0° Celsius). It would be desirable to have a better empirical understanding of this, and one approach would be to take a very small, microliter brain sample of a patient (an established harmless medical procedure) and subject it to a variety of viability assays (such as the K+/Na+ ratio). A fruitful research objective would be to achieve loading and unloading of a vitrifiable concentration of cryoprotectant in the brain and recover organized electrical activity (EEG) in a
suitable animal model and then modify this protocol for human cases. If we achieve this, viability of the brain may be retained during the descent to cryogenic temperatures.

Currently the “descent to cryogenic temperatures” is not a completely innocuous step because thermal stress-induced fracturing can still produce mechanical damage. To eliminate this form of damage and transform the challenge of reversible human cryopreservation into a biochemical problem, intermediate temperature storage appears to be a requirement.

Originally published as a column in Cryonics magazine, March, 2013