Degree of external force to the left ventricle determines hemodynamic response to nitroprusside in failing hearts: comparison with the response to dobutamine
Yamamoto, K.; Masuyama, T.; Nagano, R.; Doi, Y.; Naito, J.; Mano, T.; Kondo, H.; Hori, M.; Kamada, T.
Journal of Cardiovascular Pharmacology 26(4): 596-602
1995
ISSN/ISBN: 0160-2446 PMID: 8569221 Document Number: 454065
Vasodilators frequently, although not always, increase cardiac output (CO) in patients with congestive heart failure (CHF) despite a decrease in left ventricular (LV) diastolic pressure. In patients with CHF, vasodilator-induced decrease in LV diastolic pressure without decrease in "preload" plays an important role in the vasodilator-induced increase in CO failure that may be caused by a vasodilator-induced reduction in external force to the LV. To clarify the hypothesis that a hemodynamic response to vasodilators depends on the degree of external force to the LV in failing hearts before drug administration and to examine whether the degree of the external force also affects a hemodynamic response to positive inotropic agents, we produced in 17 dogs two different conditions of LV dysfunction with high LV end-diastolic pressure (EDP: gtoreq 15 mm Hg), i.e., 1 with high right ventricular (RV) EDP (condition 1) and the other with lower RVEDP than condition 1 (condition 2), and compared hemodynamic effects of nitroprusside or dobutamine between these two conditions. Condition 1 was produced by the injection of a small dose of microspheres into the left coronary artery and intravenous infusion of dextran. Condition 2 was produced only by the injection of a large dose of microspheres. The nitroprusside-induced decrease in LVEDP was associated with a greater decrease in RVEDP and lesser decreases in mean left atrial pressure and LV end-diastolic diameter in condition 1 than in condition 2. CO increased in condition 1; however, CO then decreased in condition 2. The nitroprusside-induced changes in CO inversely correlated with those in RVEDP (r = 0.65, p lt 0.05). Dobutamine increased CO in both conditions. Therefore, a hemodynamic response to vasodilators, in contrast to response to positive inotropic agents, depends on the degree of external force to the left ventricle before drug administration in failing hearts.