Physiological effects of hypervolemic polycythemia in newborn dogs.

The effect of hypervolemic polycythemia (Hct 62-77) on O2 transport and O2 consumption (Vo2) was studied in 16 unanesthetized newborn dogs (age 3-10 days). A control group of 10 newborn dogs (3-10 days old) was made hypervolemic but not polycythemic in an otherwise identical experiment. Hypervolemia was attained by infusing 33 ml/kg of either packed red blood cells (polycythemia) or whole blood (controls). In the polycythemic group as a result of the transfusion, cardiac output (CO) decreased by 50% (P less than 0.001), peripheral vascular resistance (PVR) increased by 170% (P less than 0.001), but O2 transport did not change significantly, and Vo2 decreased only slightly by 13% (P less than 0.01). In the 10 control animals there were no significant changes in CO, PVR, O2 transport, or Vo2 as a result of the transfusion. Blood lactate increased only slightly in experimental (35%, P less than 0.04) and control animals (23%, NS). The ability of the animals to increase their O2 transport and Vo2 was tested by measuring the changes induced by cold stress. Cold stress produced a 20% increase in Vo2 (P less than 0.05) in both the polycythemic and the control animals. Thus in spite of a decreased CO in the nonstressed state the polycythemic animals were still able to increase O2 transport and Vo2 in response to cold stress. These results suggest that the newborn animal is capable of regulating CO to maintain O2 transport appropriate to uptake under conditions of hypervolemic, polycythemic hyperviscosity, and environmental cold stress.