Conditions for Increasing Cardiac Output by Raising Aortic Blood Pressure

Abstract

Continuous infusion of isoproterenol or electric stimulation of left stellate ganglion in atropinized dogs changed the cardiac response to high aortic blood pressure. In thoracotomized dogs, cardiac output rose when ventricular systolic blood pressure was increased from 100 to more than 200 mm Hg by constriction of the descending aorta. Myocardial dimensions as measured by ultrasonic distance gauges implanted one cm apart in the left myocardium (myocardial distance) showed only slight changes. In control experiments at normal inotropic levels, or after blocking β-receptors by propranolol, the effect of increasing aortic pressure was maintenance or reduction of cardiac output. Myocardial distances were increased with reductions in amplitude of the beat-to-beat oscillations. In unanesthetized dogs, angiotensin infusion reduced cardiac output and increased myocardial dimensions under control conditions. During infusion of isoproterenol the response to angiotensin at similar increments of blood pressure was an increase in cardiac output and nearly no increase in myocardial dimensions. These studies show that the cardiac response to increased blood pressure is dependent on the level of inotropy.

Key Words:

• Angiotensin
• blood pressure
• cardiac output
• catecholamines
• isoproterenol
• myocardium
• propranolol
• stellate ganglion
• ultrasonics