Intermediate temperature storage in cryonics
The recent issue of Cryonics magazine features a comprehensive update on intermediate temperature storage (ITS). This article contains an important observation:
Acoustic events consistent with fracturing were found to be universal during cooling through the cryogenic temperature range. They occurred whether patients were frozen or vitrified. If cryoprotection is good, they typically begin below the glass transition temperature (‑123°C for M22 vitrification solution). If cryoprotective perfusion does not go well, then fracturing events begin at temperatures as warm as -90°C. Higher fracturing temperatures are believed to occur when tissue freezes instead of vitrifies because freezing increases the glass transition temperature of solution between ice crystals. The temperature at which fractures begin is therefore believed to be a surrogate measure of goodness of cryoprotection, with lower temperatures being better.
This is an important observation because one of the arguments that has been made against intermediate temperature storage is that Alcor routinely records fracturing events above the nominal glass transition temperature (Tg) of the vitrification solution. But if we recognize that such events can be (partly) attributed to ice formation due to ischemia-induced perfusion impairment it should be obvious that the recording of fracturing events above Tg as such cannot be an argument against ITS. After all, we also do not argue against the use of vitrification solutions because ice formation will still occur in ischemic patients that are perfused with vitrification solutions. Because cryonics patients almost invariably suffer some degree of ischemia prior to cryoprotective perfusion and cryopreservation, our knowledge about fracturing events in “ideal” human cases remains incomplete.
But even if ITS would only be successful in reducing fracturing events, instead of completely eliminating them, this should not be an argument against ITS. To argue that a technology should not be used because it does not completely eliminate a problem would constitute a sharp departure from the philosophy that has informed Alcor since its formation. In many areas, the evolution of Alcor’s technologies has been one of incremental evidence-based progress towards better procedures and storage conditions, not one of radical change.
The worst argument against ITS is that mature repair technologies will be able to repair clean fractures. It is a poor argument because one could similarly argue that advanced cell repair technologies will also be able to reverse the biochemical effects of short periods of ischemia and moderate degrees of ice formation. What distinguishes Alcor from other cryonics organizations is that it aims to secure viability of the brain as far into its procedures as it practically can. In ideal cases, this currently means meeting the challenge of further reducing cryoprotectant toxicity during cryoprotectant perfusion and reducing/ eliminating fracturing.
Perhaps the biggest obstacle to offering ITS to the general Alcor membership is cost. An obvious solution would be to offer ITS in addition to conventional liquid nitrogen storage. An alternative would be to gradually phase out conventional liquid nitrogen storage by no longer offering it to new neuro members and to raise cryopreservation minimums accordingly. The (preliminary) cost estimates in the article indicate that this would bring the cost of ITS for neuros closer to that of conventional liquid nitrogen whole body cryopreservation. The article does not provide specific information on the “greater capital costs” of whole body ITS systems but the reported lower liquid nitrogen consumption per patient for whole body systems suggests that it might be possible to offer whole body ITS without putting it beyond the reach of most (new) members with adequate funding.