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Regulation of oxygen delivery during induced polycythemia in exercising dogs
Journal article   Peer reviewed

Regulation of oxygen delivery during induced polycythemia in exercising dogs

JoAnn Lindenfeld, John V Weil, Victoria L Travis and Lawrence D Horwitz
American journal of physiology. Heart and circulatory physiology, Vol.289(5), pp.H1821-H1825
11/2005
DOI: 10.1152/ajpheart.01016.2004
PMID: 16006540

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Abstract

Previous studies have concluded that polycythemia decreases oxygen delivery primarily because of a large fall in cardiac output associated with a rise in systemic vascular resistance that has been attributed to increased blood viscosity. However, because other studies have shown that polycythemia may not reduce oxygen delivery, an alternative hypothesis is that cardiac output falls in response to a rising oxygen content, thereby maintaining oxygen delivery constant. To determine whether oxygen content participates in the regulation of cardiac output during polycythemia, we studied eight chronically instrumented dogs trained to exercise on a treadmill. The dogs underwent exchange transfusion with packed red blood cells containing methemoglobin, which caused an increase in hematocrit from 35 +/- 1 to 50 +/- 1% and in viscosity, with little change in oxygen content. The expected fall in exercise cardiac output failed to occur after exchange transfusion with red blood cells containing methemoglobin (7.5 +/- 4 vs. 6.8 +/- 0.5 l/min; P = not significant), and there was no rise in systemic vascular resistance. Methylene blue was then administered intravenously to facilitate conversion of methemoglobin to oxyhemoglobin, which increased oxygen content (12.8 +/- 0.9 vs. 18.4 +/- 0.9 vol%; P < 0.01) with no change in hematocrit or viscosity. Resting cardiac output did not change significantly, but there was a significant decrease in exercise output (6.8 +/- 0.5 vs. 5.8 +/- 0.4 l/min; P < 0.05). Thus we conclude that the fall in cardiac output seen in acute polycythemia results in part from the regulation of oxygen delivery and is not due solely to increased blood viscosity.
 Animals Blood Gas Analysis Blood Pressure - physiology Blood Viscosity Cardiac Output - physiology Dogs Erythrocyte Transfusion Hematocrit Hemodynamics - physiology Lactic Acid - blood Methemoglobin - metabolism Methylene Blue Muscle, Smooth, Vascular - physiology Oxygen - blood Oxygen Consumption - physiology Physical Exertion - physiology Polycythemia - metabolism

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