Norepinephrine alters exercise oxygen consumption in heart failure patients

The primary aim of this research was to evaluate the effect of acute norepinephrine (NE) infusion on the exercise oxygen utilization in heart failure patients as compared with healthy adults.

Eleven healthy adults and 10 patients with NYHA class II-III heart failure (ejection fraction <40%) who were not on beta-blocker therapy underwent steady state exercise under placebo or NE infusion conditions, followed by maximal ramp exercise testing. Oxygen utilization, hemodynamic responses, and serum lactate NE levels were evaluated.

The hemodynamic effects of NE were evident in both groups with statistically significant increases in blood pressure and concomitant decreases in heart rates. Lactate levels were higher in heart failure subjects under all conditions and steady state exercise increased levels by 24% (P = 0.04). NE infusion increased lactate levels by a nonsignificant 24% (P = 0.19). NE infusion tended to increase oxygen consumption (VO2) at the end of steady state exercise in CHF subjects (4% change; P = 0.06). Compared with healthy adults, NE infusion significantly impaired (increased) the gross VO2/W relationship in heart failure subjects (P = 0.037). There was also a modest trend for a worsening (decrease) in net efficiency after NE infusion in CHF subjects. There were no significant adverse effects of low-dose NE infusion in either group.

We conclude that 1) acute low-dose NE infusion impairs the oxygen utilization in stable heart failure patients but not in healthy adults. This may help to explain the exercise intolerance that accompanies congestive heart failure. 2) Acute infusion of low-dose NE infusion is safe and well tolerated in both healthy adults and compensated heart failure patients.