[Dose-dependent vasodilator effect of dobutamine in calves with a constant cardiac output artificial heart].

The haemodynamic effect of any drug being the resultant of its myocardial and vascular actions, it is often difficult to separate what is due to each of these components. Dobutamine is regarded as having an almost exclusive effect on the myocardium in therapeutic doses (1); its administration after implantation of an artificial heart would enable its peripheral vascular effects to be determined by exclusion of the native ventricles. Experiments were conducted on three calves weighing about 90 kg each. The artificial heart, two central venous catheters and a femoral arterial catheter were implanted under general anaesthesia. The study began on the first post-implantation day, the animals being awake, in stable haemodynamic status and with normal temperature. Dobutamine was infused through one of the venous catheter placed in the native atrium, in 6 stepwise doses of 5, 10, 15, 20, 25 and 30 mcg/kg/min, each dose being given over 10 min and separated from the other dose by a 10 min interval. The order in which these doses were administered was determined at random. By adjusting the propulsion pressure of the two ventricles and the heart rate, the cardiac output was set at a fixed value of 7.85 L/min throughout the study, this value being controlled by a computer-assisted unit. Right atrial pressure and femoral arterial were recorded during each step of the infusion. Total peripheral resistance was calculated over a stable period of the last 5 min of each dosing and before administration of dobutamine. This procedure was repeated 4 times in each calf, at intervals of 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)