Hemodynamic effects of angiotensin in intact dogs

Abstract

The hemodynamic response to angiotensin infusion in intact dogs was investigated with the thermodilution method developed in this clinic. End-diastolic volume (EDV), stroke volume (SV) and cardiac output (CO) were determined with this method, and calculations were made of the end-systolic volume (ESV), SV/EDV ratio, stroke work and power, mean ejection rate, circumference shortening, the total wall tension and the time derivative of intraventricular pressure generation (dP/dt) of the left ventricle. The moderate elevation of the mean systolic pressure (MSP) of the left ventricle (38.5 mm. Hg) was observed with the infusion rate of 0.49 μg./kg. min.; no significant change in CO, SV index (per kilogram body weight) and heart rate was seen in this range, but EDV index, ESV index, stroke work and power increased significantly. Post-infusion hypotension and tachycardia were also recorded. At the rate of 0.87 μg./kg./min., MSP was raised by 80 mm. Hg, SV index, stroke work and power all increased significantly, brady-cardia occurred, but CO, EDV index and ESV index did not change markedly. An average of 6.4 mg./kg. of Nethalide, a beta-adrenergic blocker, produced significant increases in EDV index and length of systole and significant decreases in heart rate, dP/dt and mean power. In response to angiotensin infusion under the blockade, increases in MSP, dP/dt, stroke work and power were shown to be somewhat less, but EDV index and ESV index increased proportionately with the rate of infusion. The correlation between EDV index and ESV index and the correlation between the total tension of the left ventricle at the end of systole and either EDV index or ESV index was good in all experiments studied. Stroke power and work increased roughly parallel to EDV index, and with the beta blockade a depressed function curve was observed. Complexity of the cardiovascular control mechanism and importance of the sympathetic innervation were briefly discussed.