AJP - Heart and Circulatory Physiology, Vol 245, Issue 5 814-H823, Copyright © 1983 by American Physiological Society
Regional venous return: nitroprusside effect in normal and chronically congested dogs
R. L. Engler, G. L. Freeman and J. W. Covell
The venous circulation is a key determinant of cardiac loading conditions.
Although it may be altered by chronic congestive heart failure and
vasodilating drugs, the mechanisms of these alterations have not been
thoroughly studied, and their exact nature is unclear. We used venous
return curves characterized by the pressure at zero flow (PZF) and
resistance to venous return (RVR) to study the effect of nitroprusside and
chronic congestion on regional venous return from the splanchnic and
superior vena cava (systemic) venous beds in dogs. Chronic venous
congestion was induced by prior creation of tricuspid insufficiency and
pulmonic stenosis (TIPS). Nitroprusside lowered splanchnic PZF but not
systemic PZF in both normal and TIPS animals. In normal animals systemic
RVR increased during nitroprusside infusion but was unchanged in the
congested animals. Resting values of PZF and RVR were different in the
splanchnic and systemic venous beds in both normal and TIPS animals. We
conclude that 1) nitroprusside works to selectively lower PZF in the
splanchnic venous bed, 2) the regionally specific site of action of
nitroprusside is not altered by TIPS, and 3) the independent behavior of
the venous parameters of the two beds represents an important mechanism for
the control of cardiac output.
