Effects of Catecholammes on Hemodynamics and Myocardial Contractility in Dogs

Catecholamines play an important role in main-trance of circulatory function and are widely employed in treatment of shock states. There have been many experimental studies on cardiovascular effects of catecholamines. However, few has been reported on comprehensive observations of their hemodynamic effects in animals maintaining normal circulation. The purpose of the present study is to investigate the effects of catecholamines on hemodynamics and myocardial contractility in special reference to influence of different dosage and manners of administration. Methods Adult mongrel dogs anesthetized with intraperitoneal pentobarbital sodium (30 mg/kg) were subjected to thoracotomy under artificial respiration. The following six tracings were simultaneously recorded on an electromagnetic oscillograph; (1) aortic blood flow curves with the probe of an electromagnetic flowmeter fixed around the aortic root, (2) aortic blood pressure curves with a catheter tip lodged in the left common carotid artery, (3) left atrial pressure curves with a catheter inserted in the left atrial appendage, (4) left ventricular cavity through the apex, (5) the first derivatives of the left ventricular pressure using an R-C differentiating circuit whose time constant was 0.5 msec, and (6) unipolar left ventricular epicardial electrocardiogram. These simultaneous tracings were analyzed for the following parameters; the heart rate, aortic blood pressure and flow, stroke volume, mean left atrial pressure, left ventricular external power, stroke work, Isometric Time-Tension Index [(dp/dt)/IIT], and total peripheral vascular resistance. A catheter lodged in the femoral vein was used for intravenous administration of catecholamines. For evaluation of the effects of a single bolus dose of the drugs, each of eight dogs was subjected, at an interval of 5 to 8 minutes, to rapid intravenous injections of six different drug-dose combinations (0.1 and 0.8 μg/kg of ISP, EP and NE). The effects of sustained intravenous infusion of NE was also investigated. A constant flow pump was employed for intravenous infusion of 5% dextrose solution for 3 hours throughout the experiment. Control data was obtained during the first one hour when only the dextrose solution was infused. NE was given at a rate of 0.8 μg/kg/min for the next one hour. For the last one hour continuous observation was also made with the dextrose solution alone infused. A similar experiment was also performed in spinal dogs who had undergone ligation of the bilateral vertebral arteries and disconnection of the bilateral cervical vagus nerves and the spinal cord at the level of the second cervical vertebra.