Improved O2 Transfer to Tissues During Deep Hypoxia in Rats with a Left-Shifted Blood O2 Dissociation Curve
Oxygen is transported in blood while bound to a highly specialized carrier, the hemoglobin in the red cells. The loading of hemoglobin with O2 in the lung depends on the partial pressure of O2 in the alveolar air. During hypoxic hypoxia this pressure remains lowered in spite of hyperventilation, so that if the total transfer of O2 from the lung to tissues is to be guaranteed, either the loading of blood with O2 in the lung must be enhanced, or blood flow through the lung or O2 extraction in tissues must increase. It is well known that the extraction of O2 from blood has its limits which are different in different organs. During hypoxic hypoxia, an increase of the loading ability of blood in the lung or of blood flow through the lung is required to compensate for the decrease of Po2 in the alveolar air. The loading ability of blood can be enhanced by an increase of blood O2 carrying capacity accompanied by polycythemia, or by an increase of blood O2 affinity, i.e., a shift of the blood O2 dissociation curve (ODC) to the left. The former is the usual reaction of many mammalian species to chronic hypoxia, with the potential danger that excessive polycythemia may increase blood viscosity to such a degree that flow may become limited. An increase of blood O2 affinity improves the loading in the lung but impairs the unloading in tissues.
KeywordsDissociation Curve Severe Hypoxia Alveolar Ventilation Capacitance Coefficient Hypoxic Hypoxia
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