Effects of vasculature and blood composition on the response of biological systems to low temperatures.

摘要

nimals encounter low temperatures as part of their normal life or by accident. Knowledge on how animals respond to these cold environments can aid us in our understanding of survival strategy and provide information on how to improve procedures in the practical applications of low temperatures in medicine. This study examines three special cases of cold resistance strategies in animals with emphasis on the effects of the vasculature and blood composition.;First, the effect of the extremity vasculature of the newborn infant (full-term and low-weight) is studied in the context of their response to hypothermia. Combining the recent revelations of the importance of the blood vessel's dimensions in their bioheat transport contribution, with a simple analytical model using the infant's smaller vascular dimensions, the efficiency of their vascular response to cold is evaluated.;Second, the freeze-tolerant wood frog (Rana Sylvatica) is considered. Possessing a similar organ structure to the mammal, the study of the wood frog represents a unique opportunity for its implications in cryopreservation. Although the successful preservation of organs has eluded investigators, evolution has developed its own solutions to this problem. Here, a mathematical model is developed for the process of freezing in the frog which combines both heat and mass transport phenomena during phase transition in bulk tissues. These equations are solved through linearization and numerical techniques. Implications of the results are discussed in the context of both cryosurgery and cryopreservation.;Finally, the properties of the thermal-hysteresis proteins found in the blood of freeze-avoiding polar fishes are investigated. Here, the property of viscosity is studied in blood plasma samples and in aqueous solutions containing thermal-hysteresis proteins at temperatures where they are naturally active. Since these proteins are only available in small quantities, a new Lamb-wave microsensor system is used to measure viscosity in