Cardiac responsiveness to β-adrenergic stimulation in experimental anemia

Abstract

Cardiac reactivity of β-adrenergic stimulation was assessed by isoproterenol dose–response curves (dose range 0.025–0.4 μg/kg) before and 1 h after the rapid induction of anemia in dogs anesthetized with halothane:N₂O:O₂. Anemai (hematocrit = 16 ± 4%) was induced by an isovolumic exchange transfusion with Dextran 70, and was followed by significant increments in cardiac output (+57 ± 9%), max dP/dt of the left ventricle (+37 ± 7%), and in peak acceleration of blood flow in the ascending aorta (+46 ± 13%). Anemia was associated with a significant reduction of the chronotropic responses to all but the lowest dose of isoproterenol. The simultaneously determined inotropic responses (max dP/dt) where the same before and after the induction of anemia. The responses in terms of peak acceleration of aortic blood flow tended to be greater in the anemic than in the control phase, at all dose levels used. These findings indicate that in rapidly induced experimental anemia the heart is capable of responding to marked degrees of β-adrenergic stimulation, representing a more than twofold increase in the dP/dt.