Angiotensin-converting enzyme inhibition, autonomic activity, and hemodynamics in patients with heart failure who perform isometric exercise.

Effects of angiotensin-converting enzyme inhibition (ACEI) on autonomic responses and hemodynamics in patients with congestive heart failure (CHF) subjected to isometric exercise have not been studied. We tested whether acute ACEI might influence the effects of isometric exercise in patients with CHF. In the first part of the study we showed that isometric exercise increased blood pressure in the control group and in the CHF group, whereas cardiac output increased only in the control group. Stroke volume remained unchanged in the control group, whereas it decreased significantly in CHF group. We next analyzed the effect of acute ACEI (5 mg ramipril) on the decrease in cardiac output during isometric stress in patients with CHF. During isometric exercise mean blood pressure and heart rate increased similarly in both groups. However, cardiac output decreased during placebo by -0.48 +/- 0.12 L/min (p < 0.01) but not during ACEI. Spectral analysis of blood pressure showed an increase (p < 0.01) in the high-frequency parasympathetic component from 7.3% +/- 3.6% to 18.1% +/- 9.5% after ACEI. norepinephrine plasma levels increased after isometric stress in the placebo group, whereas other hormones did not change. ACEI prevented the norepinephrine increase after isometric stress. Thus the decrease in cardiac output during isometric exercise in patients with CHF was prevented by acute ACEI. The effect of ACE inhibition may be related to reduced sympathetic activity.