| Summary: | Diving mammals share with fetal and newborn animals a high resistance to asphyxia when compared, respectively, with terrestrial and adult animals. Adaptations for conservation or sparing of oxygen and for adjustment to the effects of accumulated metabolic products, such as carbon dioxide and hydrogen ions, have been discovered in both diving marine mammals and asphyxiated terrestrial species. The major requirement in all instances of prolonged oxygen deprivation is for protection of the least resistant vital organs, the brain and the heart. Dawes has recently reviewed the evidence supporting the view that integrity of the circulation contributes importantly to survival time of the asphyxiated fetus or newborn. ' The mechanism is dependent on the concentration of glycogen in cardiac muscle before the asphyxial episode, ' and requires an adequate circulatory supply of glucose to the brain for glycolytic energy production. Survival is shortened by blocking glycolysis with iodoacetate and prolonged by the administration of additional glucose when
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