Neonatal Deep Hypothermia: Heart Function and Metabolism
We present evidence, based particularly on studies of Peromyscus leucopus, that neonatal rodents in deep hypothermia (T b ≤ 7°C)—although apneic—steadily take up O2 across the lungs and distribute it via the circulatory system. We argue that the myocardium, respiratory rhythmogenic neurons, and possibly other vital tissues depend for their survival during deep hypothermia on this continuing O2 supply. In regards their steady O2 uptake and its significance, neonatal rodents resemble rodent hibernators during deep hypothermia. However, details differ strikingly. Neonates, having stopped breathing on entry to hypothermia, take up O2 via the mouth and nares by apneic mechanisms. Moreover, neonates lose sinoatrial (SA) pacing of ventricular contraction on entry to hypothermia and depend on quasi-rhythmic ventricular escape contractions to maintain cardiac activity. During deep hypothermia, physiologically limited mechanisms of respiratory and circulatory O2 transport combine to provide neonate tissues with a limited rate of O2 supply that is vitally important.
KeywordsBrown Adipose Tissue Ventricular Contraction Prairie Vole Deep Hypothermia Microtus Ochrogaster
The success of this research depended on contributions from Michael Cook, Susan Hill, Brock Horsley, and Bradley White. Vincent Shaw and Daphne Swope helped with manuscript preparation. George Eyster and David Matisoff, both clinical cardiologists, provided invaluable assistance with interpretation of EKGs. Much gratitude to all.
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