Journal of Applied Physiology, Vol 69, Issue 5 1578-1586, Copyright © 1990 by American Physiological Society
Distribution of blood flow during exercise after blood volume expansion in swine
K. I. Norton, M. D. Delp, M. T. Jones, C. Duan, D. R. Dengel and R. B. Armstrong
Exercise Biochemistry Laboratory, University of Georgia, Athens 30602.
To study the distribution of blood flow after blood volume expansion, seven
miniature swine ran at high speed (17.6-20 km/h, estimated to require 115%
of maximal O2 uptake) on a motor-driven treadmill on two occasions: once
during normovolemia and once after an acute 15% blood volume expansion
(homologous whole blood). O2 uptake, cardiac output, heart rate, mean
arterial pressure, and distribution of blood flow (with radiolabeled
microspheres) were measured at the same time during each of the exercise
bouts. Maximal heart rate was identical between conditions (mean 266); mean
arterial pressure was elevated during the hypovolemic exercise (149 +/- 5
vs. 137 +/- 6 mmHg). Although cardiac output was higher and arterial O2
saturation was maintained during the hypervolemic condition (10.5 +/- 0.7
vs. 9.3 +/- 0.6 l/min), O2 uptake was not different (1.74 +/- 0.08 vs. 1.74
+/- 0.09 l/min). Mean blood flows to cardiac (+12.9%), locomotory (+9.8%),
and respiratory (+7.5%) muscles were all elevated during hypervolemic
exercise, while visceral and brain blood flows were unchanged. Calculated
resistances to flow in skeletal and cardiac muscle were not different
between conditions. Under the experimental conditions of this study, O2
uptake in the miniature swine was limited at the level of the muscles
during hypervolemic exercise. The results also indicate that neither
intrinsic contractile properties of the heart nor coronary blood flow
limits myocardial performance during normovolemic exercise, because both
the pumping capacity of the heart and the coronary blood flow were elevated
in the hypervolemic condition.
