Effect of Saline Infusion on Stroke Volume and End-Systolic Volume at Various Levels of Adrenergic Activity in Dogs

Abstract

The effect of saline infusion at rates of 60 ml/min was studied in anesthetized, open-chest and conscious dogs. Ventricular end-diastolic and end-systolic volumes (EDV and ESV) were estimated from ultrasonic recordings of myocardial distances and thermodilution methods. Changes in stroke volume and EDV were closely related. About 25 per cent of the increase in stroke volume induced by saline loading could be attributed to a rise in EDV, and 75 per cent to increased myocardial shortening. In adrenergically stimulated animals (constant isoproterenol infusion, or stimulation of left stellate ganglion), the increase in ESV associated with a rise in EDV was only half as large as in control experiments or after propranolol administration. It is concluded that the Frank-Starling mechanism becomes more sensitive in regulating stroke volume at high adrenergic activity on account of better maintenance of ESV.

Key Words:

• Adrenergic activity
• cardiac dimensions
• cardiac output
• isoproterenol
• myocardium
• preload
• propranolol
• thermodilution
• ultrasonics
• ventricular contractility
• ventricular volume