Graded infusions of dobutamine in conscious sheep increased both the extent and velocity of myocardial contraction at low doses, whereas only velocity increased at higher doses.
Does graded dobutamine infusion alter the extent and velocity of myocardial contraction in conscious sheep?
In a conscious sheep model, low-dose dobutamine increases both the extent and velocity of myocardial contraction, while high-dose dobutamine only increases contraction velocity.
The shortening- and shortening rate-preload-afterload relations, based on the concept of the myocardial end-systolic stress-strain relation (ESSSR), are a newly developed load- and size-independent assessment of myocardial contractility. The purpose of this study was to apply this assessment to compare extent and velocity of myocardial contraction during graded infusions of dobutamine. Seven chronically instrumented unsedated sheep were studied at rest and during graded infusions of dobutamine (2.5-20 micrograms.kg-1.min-1). The ESSSR were linear over a wide range of load alterations, whereas the end-systolic pressure-diameter relations (ESPDR) were generally nonlinear. Midwall shortening rate (SRm) at common preload and afterload representing contraction extent increased with each dose of dobutamine through 20 micrograms.kg-1.min-1. In contrast, midwall shortening (Sm) increased through dobutamine 5 micrograms.kg-1.min-1 but not at higher dobutamine infusion rates. Conventional endocardial shortening and the slope of the ESPDR, fitted to a linear model, exhibited responses similar to Sm. The velocity of circumferential endocardial fiber shortening (Vcf,c), Vcf,c-afterload relation, and maximum first derivative of left ventricular pressure exhibited responses similar to SRm. Thus both the extent and velocity of contraction increased at low doses of dobutamine, whereas only the velocity increased at high doses. Potential mechanisms for the saturated response of the extent of contraction include 1) shorter systolic time for contraction due to earlier onset of relaxation and 2) the utilization of myocardial contractile energy for left ventricular wall deformation at small cavity volumes at high doses of dobutamine.
Aoyagi et al. (Thu,) reported a other. Dobutamine vs. Rest was evaluated on Extent and velocity of myocardial contraction. Graded infusions of dobutamine in conscious sheep increased both the extent and velocity of myocardial contraction at low doses, whereas only velocity increased at higher doses.