Systemic vascular effects of epinephrine administration in man

Area of Science:

• Cardiovascular Physiology
• Pharmacology

Background:

• Peripheral vascular effects of epinephrine are well-studied in animals but not humans.
• Understanding these effects in humans requires independent control of flow and pressure, achievable during cardiopulmonary bypass.

Purpose of the Study:

• To determine the peripheral vascular effects of epinephrine in humans.
• To analyze vascular compliance, resistance, and time constants under epinephrine infusion.
• To investigate the mechanism of epinephrine-induced increase in cardiac output.

Main Methods:

• Studied nine anesthetized patients on cardiopulmonary bypass before and during epinephrine infusion.
• Measured blood pressure, reservoir volume, vascular compliance, and venous resistance.
• Analyzed transient blood volume changes to identify vascular compartments and time constants.
• Utilized Thallium-201 imaging in volunteers to localize vascular compartments.

Main Results:

• Epinephrine infusion increased blood pressure and reservoir volume, decreasing systemic vascular compliance due to venoconstriction.
• Venous return resistance decreased.
• Epinephrine redistributed blood flow from a long time constant compartment to a short one, increasing venous return.
• Imaging suggested mesenteric and muscle beds as potential long and short time constant compartments.

Conclusions:

• Epinephrine increases cardiac output in humans primarily by redistributing blood flow, independent of direct cardiac effects.
• The study provides the first direct analysis of epinephrine's peripheral vascular effects and circulatory compartment models in humans.