AJP - Heart and Circulatory Physiology, Vol 257, Issue 3 726-H733, Copyright © 1989 by American Physiological Society
Myocardial and systemic responses to arterial hypoxemia during cardiac tamponade
G. J. Crystal and M. R. Salem
Department of Anesthesiology, Illinois Masonic Medical Center, Chicago 60657.
Experiments were performed on 14 anesthetized, open-chest dogs to assess
myocardial and systemic responses to cardiac tamponade alone (TAMP) and
combined with arterial hypoxemia (HYP). Regional blood flow (RBF) was
measured with radioactive microspheres and used to compute regional O2
supply. Myocardial oxygen and lactate extraction were determined.
Myocardial oxygen consumption (MVO2) was calculated with Fick equation. An
increase in pericardial pressure, sufficient to reduce mean aortic pressure
(MAP) by 20%, caused proportional decreases in myocardial RBF and MVO2 but
had no effect on endo-to-epi flow ratio or on myocardial lactate
extraction. TAMP alone decreased RBF and O2 supply in kidney, splanchnic
organs, skeletal muscle, and skin, but it had no effect in brain. HYP
(arterial PO2, 35 +/- 2 mmHg) during TAMP restored MAP and caused
transmurally uniform increases in myocardial RBF that were adequate to
maintain MVO2 and lactate extraction. RBF increased sufficiently in brain
to maintain regional O2 supply, whereas unchanged or inadequate increases
in RBF in other tissues accentuated reductions in O2 supply. During
combined TAMP and HYP, local vasodilator mechanisms were capable of
maintaining adequate oxygen supply in myocardium and brain but not
apparently in the nonvital tissues where these mechanisms were antagonized
by reflex vasoconstriction.
