Effect of Epinephrine on Pressure, Flow, and Volume Relationships in the Systemic Circulation of Dogs

Abstract

The effect of epinephrine on peripheral circulation was studied in ten anesthetized open-chest dogs. Blood flow and right atrial pressure were independently controlled by a right heart bypass; changes in blood volume could be precisely determined from the changes occurring in the bypass reservoir. At constant blood flow and right atrial pressure, a constant infusion of epinephrine (5.8 µg/kg min^-1) decreased blood volume by an average of 208 ml. During epinephrine infusion, the ratio of changes in blood volume to changes in blood flow measured at constant right atrial pressure, (ΔV/ΔQ^·)_Pra, decreased from 0.226 minutes to 0.153 minutes and the ratio of changes in blood volume to changes in right atrial pressure at constant blood flow, the vascular compliance, decreased from 27.1 ml/cm H₂O to 20.7 ml/cm H₂O. Transient changes in blood volume following a step decrease in right atrial pressure at constant blood flow showed that blood was draining from two vascular compartments with different time constants: 0.059 minutes and 0.388 minutes before epinephrine infusion and 0.058 minutes and 0.486 minutes during epinephrine infusion. We analyzed the data using a mathematical model of the peripheral circulation consisting of two compartments with different time constants. The analysis showed that the primary effect of epinephrine on the systemic circulation was to redistribute blood flow away from the compartment with the longest time constant. The reduction in (ΔV/ΔQ^·)_pra and the decrease in blood volume at constant flow and right atrial pressure were essentially determined by the change in flow distribution brought about by a change in arteriolar tone and not by a change in venous tone.