Time Limiting Boundaries of Reversible Clinical Death in Rats Subjected to Ultra-Deep Hypothermia.

BACKGROUND: It is well known that body temperature maintenance between 20 and 35°C prevents hypoxic damage. However, data regarding the ideal duration and permissible temperature boundaries for ultra-deep hypothermia below 20°C are rather fragmentary. The aim of the present study was to determine the time limits of reversible clinical death in rats subjected to ultra-deep hypothermia at 1-8°C. RESULTS: Rat survival rates were directly dependent on the duration of clinical death. If clinical death did not exceed 35 min, animal viability could be restored. Extending the duration of clinical death longer than 45 min led to rat death, and cardiac functioning in these animals was not recovered. The rewarming rate and the lowest temperature of hypothermia experienced did not directly influence survival rates. CONCLUSIONS: In a rat model, reversible ultra-deep hypothermia as low as 1-8°C could be achieved without the application of hypercapnia or pharmacological support. The survival of animals was dependent on the duration of clinical death, which should not exceed 35 min.

Influence of helium, xenon, and other noble gases on cryopreservation of Hela and l929 cell lines.

Any biological material contains dissolved gases that affect physical and biological processes associated with cooling and freezing. However, in the cryobiology literature, little attention has been paid to the effect of gasses on cryopreservation. We studied the influence of helium, neon, krypton, xenon, argon, nitrogen, and sulfur hexafluoride on the survivability of HeLa and L929 cell lines during cryopreservation. Saturation of a cell suspension with helium, neon, and sulfur hexafluoride enhanced survival of HeLa and L929 cells after cryopreservation. Helium exerted the most significant effect. For a range of noble gases, the efficiency of the positive effect decreased as the molecular mass of the gas increased. This paper discusses possible mechanisms for the influence of gases on the cryopreservation of biological material. The most probable mechanism is the disruption of the frozen solution structure with gas-filled microbubbles produced during water crystallization. Ultimately, it was concluded that helium and neon can be used to improve methods for cryopreservation of cell suspensions with a low concentration of conventional penetrating cryoprotectants or even without them.