AJP - Heart and Circulatory Physiology, Vol 241, Issue 6 857-H863, Copyright © 1981 by American Physiological Society
Reflex sympathetic augmentation of left-ventricular inotropic state in the conscious dog
C. Yoran, L. Higginson, M. A. Romero, J. W. Covell and J. Ross Jr
Cardiac reflex responses to a series of partial inferior vena caval
occlusions were studied in conscious previously instrumented dogs. Heart
rate responses during the fall of systemic arterial pressure were mediated
both by increased sympathetic tone and withdrawal of parasympathetic tone.
Responses of the left-ventricular inotropic state, estimated from changes
in left ventricular pressure rise (LV dP/dt), were studied early after
release of a series of partial vena caval occlusions, and a positive linear
relation between the prior fall in the systemic arterial pressure and the
increase in LV dP/dt was demonstrated. Serial studies showed this effect of
persist for at least 12 s beyond the reflex slowing of heart rate early
after release of vena caval occlusion. The positive inotropic response was
markedly attenuated by beta-adrenergic blockade and also occurred at a
constant heart rate. It was present after adrenalectomy. These studies
suggest that the integrated baroreceptor responses that are activated by a
simultaneous decrease in the venous return and systemic arterial pressure
play an important role in the regulation of left-ventricular inotropic
state in the conscious dog.
