[Physiological mechanisms for maintaining the body's energy requirements during reduced blood hemoglobin levels]

Energy expenditure and O2 consumption, the tidal volume of cardiac output (Q) and the respiration (VE), the arterio-venous difference in O2 content, the arterial and venous blood gases, and the survival of animals in graded decrease of the hemoglobin concentration in the vascular bed (hemodilution) were studied in anesthetized Wistar rats as well as the values of oxygen available in the brain tissue. The animals were shown to maintain the initial level of energy expenditure by means of the Q increase up to reducing the hemoglobin concentration from 16.2 g/dl to 4.9 g/dl (hematocrit 12.9%). The elements of oxygen insufficiency, however, as measured by the Q and VE responses as well as by changes in oxygen available in mixed venous blood and in brain tissue, become evident yet in early stages of the hemodilution.