Metabolic Reduction in Hypothermia: Pathophysiological Problems and Natural Examples - Part 1

Abstract

Following a description of the protective effects of hypothermia, the limitations resulting from "cold swelling" of the brain, caused by a progressive discrepancy between active and passive cellular transport processes, are discussed. The observation that the tolerable limits of metabolic reduction lie well below the normal turnover rates leads to a short survey of the evolution of energy metabolism. The gradual development of the latter from anaerobiosis to aerobiosis and from poikilothermy to homeothermy apparently provides the background for transient reductions to lower rates which spontaneously occur even in higher vertebrates. As an impressive example of such a natural strategy, the anaerobic survival of diving turtles is outlined which essentially depends on an efficient buffering. This dependence bears analogy to cardioplegia, where an increase in buffering capacity can greatly retard the fall of energy turnover, thus leading, as is shown by microcalorimetry, to an intermediate plateau of anaerobic metabolism.