Evidence in cryonics is a complicated concept. For starters, it is not possible to “prove” cryonics will work, here and now, because the fundamental idea of cryonics is to stabilize critically ill patients (people considered “dead” by less rigorous criteria) in anticipation of more advanced future medical technologies. What we can do is validate cryonics technologies with reversible cryopreservation (“suspended animation”) as a benchmark. As a general rule, we can state that we make progress in cryonics when stabilization, cryopreservation, and maintenance (“storage”) technologies cause less damage than the technologies that preceded them. But how do we know if this is the case?
The most rigorous form of validation, human clinical trials, is usually not available in cryonics. There are often new (approved) emergency medical technologies, however, that can be modified to be used in cryonics procedures. A major advantage of adopting such technologies is that the validation has already been done by other organizations or companies. Examples of such technologies will often fall under the rubric of emergency medicine. For example, an FDA-approved technology that improves blood flow during cardiopulmonary resuscitation can be added to Alcor’s stabilization equipment to improve stabilization procedures.
One step down from rigorously designed human clinical trials are animal studies. In cryonics we often make a distinction between small animal studies (e.g., mice, rats) and large animal studies (e.g., pigs, dogs) etc. It seems common sense to think that large mammals provide stronger evidence for a technology than smaller animals but the real issue at stake here is not how large an animal is but how closely an animal model tracks what happens in humans. For example, if cat brains have an uncharacteristically high tolerance for cerebral ischemia, the (smaller) rat may actually be a more realistic model for validating neuroprotective strategies in humans.
One area where choosing the correct animal model has proven itself to be of crucial importance concerns the effect of cryoprotectants on the brain. Most mammalian species experience dehydration of the brain after equilibration with a vitrification agent. Because it is reasonable to assume that severe dehydration adversely affects brain viability it is tempting to select an animal model that experiences little cryoprotectant-induced dehydration. But one thing that we have learned from burhole measurements and CT scans in human cryonics patients is that under optimal conditions cryoprotective perfusion with both glycerol and the modern vitrification agents produces severe shrinkage of the brain. So if we want to validate strategies to eliminate this dehydration the most important consideration is not how “large” the animal is but how well the animal tracks the effects of cryoprotectants on the human brain.
Most technologies in cryonics need to be evaluated with ultrastructure and/or viability as an endpoint. But there are also new developments in cryonics where such a benchmark would not make a lot of sense. For example, if we build a new patient enclosure to keep the patient cold during cryoprotective perfusion we can just measure the core temperature of the patient to see if we have done a satisfactory engineering job. Another example is the design of new dewars where we can look at variables like the boiloff rate and long-term durability of the design.
In conclusion, there are a number of ways to validate new technologies in cryonics. If a new technology has undergone human clinical trials we often can just adapt that technology for cryonics without designing new experiments. In the case of more cryonics-specific technologies animal studies can be conducted and the choice of animal model will be dictated by how close a model tracks what we know to occur in humans (among other considerations like ethics and cost). Finally, when a new development in cryonics is mostly an engineering challenge, validating its efficacy is often just an issue of doing basic physiological measurements or practical tests.
Originally published as a column in Cryonics magazine, August, 2014