Ventilation-perfusion relationships during induced normovolemic polycythemia in dogs

Previous studies on normal subjects and patients with polycythemia have given conflicting results of the effect of polycythemia on pulmonary gas exchange. We studied acutely induced normovolemic polycythemia in the dog and measured arterial blood gases and ventilation-perfusion (VA/Q) relationships using the multiple inert gas elimination technique. The mean base-line hematocrit of 43 +/- 5% was increased to 57 +/- 4 and 68 +/- 8%, respectively, after two exchange transfusions of packed erythrocytes. Subsequent plasma exchange transfusions returned the mean hematocrit to 44 +/- 4%. Polycythemia caused no significant arterial hypoxemia; indeed there was a slight improvement in the alveolar-arterial PO2 difference. The multiple inert gas elimination measurements showed no increase in VA/Q inhomogeneity with no increase in log SD ventilation (V) or log SD blood flow (Q). There was a shift of mean V and mean Q to high VA/Q areas because of a decrease in cardiac output, presumably caused by increased blood viscosity. This study showed no deleterious effects on pulmonary gas exchange within the hematocrit range of 36-76%.