AJP - Heart and Circulatory Physiology, Vol 252, Issue 6 1164-H1174, Copyright © 1987 by American Physiological Society
Cardiac adjustments to left-side inotropic stimulation of in situ pig hearts
O. A. Vengen, K. Lande, O. Ellingsen and A. Ilebekk
Cardiac adjustments to inotropic stimulation of the left side of the heart
by continuous infusions of isoproterenol (0.6-0.8 microgram/min) and
calcium chloride (240 mumol/min) into the left coronary artery were
examined in open-chest pigs (17-36 kg) anesthetized with pentobarbital
sodium. Both agents caused a reduction in the left ventricular (LV) preload
and preejection segment length (PESL). Stroke volume (SV) rose by only 1.2
ml from 15.9 ml (P less than 0.01) during isoproterenol infusion, but when
the reduction in LV PESL of 3.2% (P less than 0.01) was restored by saline
infusion, SV increased by 27%. The LV PESL reduction was less at
hypervolemia than at normovolemia. A computer-based model of the
circulation predicted most of these changes and suggested redistribution of
blood from the pulmonary to the systemic circulation. During isoproterenol
infusion, the pulmonary arterial pressure fell, and the right ventricular
end-ejection segment length declined. Reduced right ventricular afterload
thus appears to be an important mechanism by which right ventricular output
is increased during a selective increase in LV inotropy.
