DEGREE OF EXTERNAL FORCE TO THE LEFT-VENTRICLE DETERMINES HEMODYNAMIC-RESPONSE TO NITROPRUSSIDE IN FAILING HEARTS - COMPARISON WITH THE RESPONSE TO DOBUTAMINE
K. Yamamoto et al., DEGREE OF EXTERNAL FORCE TO THE LEFT-VENTRICLE DETERMINES HEMODYNAMIC-RESPONSE TO NITROPRUSSIDE IN FAILING HEARTS - COMPARISON WITH THE RESPONSE TO DOBUTAMINE, Journal of cardiovascular pharmacology, 26(4), 1995, pp. 596-602
Vasodilators frequently, although not always, increase cardiac output
(GO) in patients with congestive heart failure (CHF) despite a decreas
e in left ventricular (LV) diastolic pressure. In patients with CHF, v
asodilator-induced decrease in LV diastolic pressure without decrease
in ''preload'' plays an important role in the vasodilator-induced incr
ease in CO failure that may be caused by a vasodilator-induced reducti
on in external force to the LV. To clarify the hypothesis that a hemod
ynamic response to vasodilators depends on the degree of external forc
e to the LV in failing hearts before drug administration and to examin
e whether the degree of the external force also affects a hemodynamic
response to positive inotropic agents, we produced in 17 dogs two diff
erent conditions of LV dysfunction with high LV end-diastolic pressure
(EDP: greater than or equal to 15 mm Hg), i.e., 1 with high right ven
tricular (RV) EDP (condition 1) and the other with lower RVEDP than co
ndition 1 (condition 2), and compared hemodynamic effects of nitroprus
side or dobutamine between these two conditions. Condition 1 was produ
ced by the injection of a small dose of microspheres into the left cor
onary artery and intravenous infusion of dextran. Condition 2 was prod
uced only by the injection of a large dose of microspheres. The nitrop
russide-induced decrease in LVEDP was associated with a greater decrea
se in RVEDP and lesser decreases in mean left atrial pressure and LV e
nd-diastolic diameter in condition 1 than in condition 2. CO increased
in condition 1; however, CO then decreased in condition 2. The nitrop
russide-induced changes in CO inversely correlated with those in RVEDP
(r = 0.65, p < 0.05). Dobutamine increased CO in both conditions. The
refore, a hemodynamic response to vasodilators, in contrast to respons
e to positive inotropic agents, depends on the degree of external forc
e to the left ventricle before drug administration in failing hearts.