Journal of Applied Physiology, Vol 58, Issue 3 749-758, Copyright © 1985 by American Physiological Society
Effects of transfusion-induced polycythemia on O2 transport during exercise in the dog
P. T. Schumacker, B. Guth, A. J. Suggett, P. D. Wagner and J. B. West
An increased hematocrit could enhance peripheral O2 transport during
exercise by improving arterial O2 content. Conversely, it could reduce
maximal delivery of O2 by limiting cardiac output during exercise or by
limiting the distribution of blood flow to peripheral capillaries with high
O2 extractions. We studied O2 transport at rest and during graded treadmill
exercise in splenectomized tracheostomized dogs at normal hematocrit (38
+/- 3%), and 48 h after transfusion of type-matched donor cells. This
procedure increased hematocrit (60 +/- 3%) but also increased blood volume
(P less than 0.05). Following transfusion, resting cardiac output (QT) and
heart rate were not different. During exercise, QT was significantly lower
at each level of O2 consumption (VO2) at high hematocrit (P less than
0.01). A reduction in QT was also seen during polycythemic exercise with
hypoxemia produced by breathing 12 or 10% O2 in N2. Despite the reduction
in QT, mixed venous PO2 was not lower at high hematocrit, and the increase
in base deficit with VO2 was not different from control measurements. O2
delivery (QT X arterial content) was similar at each level of VO2 at both
levels of hematocrit, during both normoxic and hypoxic studies. Both
systemic and pulmonary arterial pressures were increased at rest after
transfusion (P less than 0.05). However, pulmonary and systemic pressures
were not higher than control during exercise at high hematocrit. We
conclude that a hematocrit of 60% with increased blood volume is not
associated with a cardiac limitation of O2 delivery, nor does it interfere
with peripheral O2 extraction during exercise in the dog.
