| Abstract: | The hemodynamic effects of three different infusion rates of epinephrine (25, 50, or 100 ng X kg-1 X min-1 for 14 min) were examined in 10 normal human subjects. Ejection fraction and changes in cardiac volumes were assessed by radionuclide ventriculography. Plasma epinephrine was increased to levels that spanned the normal physiological range (178 +/- 15, 259 +/- 24, and 484 +/- 69 pg/ml, respectively). Epinephrine infusions resulted in dose-dependent increases in heart rate (8 +/- 3, 12 +/- 2, and 17 +/- 1 beats/min, mean +/- SE) and systolic pressure (8 +/- 1, 18 +/- 2, and 30 +/- 6 mmHg). Although epinephrine infusions had minimal effects on end-diastolic volume, there were significant increases in stroke volume (+26 +/- 2, 31 +/- 4, and 40 +/- 4%), ejection fraction (+0.10 +/- 0.01, 0.14 +/- 0.02 and 0.16 +/- 0.03 ejection fraction units), and cardiac output (+41 +/- 4, 58 +/- 5, and 74 +/- 1%). These increases in left ventricular performance were associated with a decreased systemic vascular resistance (-31 +/- 3, -42 +/- 2, and -48 +/- 8%). Supine bicycle exercise resulted in similar plasma epinephrine levels (417 +/- 109 pg/ml) and similar changes in stroke volume, ejection fraction, and systemic vascular resistance but greater increases in heart rate and systolic blood pressure. Since infusion-associated hemodynamic changes occurred at plasma epinephrine levels commonly achieved during many types of physical and emotional stress, epinephrine release may have an important role in regulating systemic vascular resistance, stroke volume, and ejection fraction responses to stress in man. |
