The effects of clonidine on arterial baroreflex sensitivity and cardiopulmonary baroreflex control of sympathetic nerve activity in patients with left ventricular dysfunction.

Background:   Clonidine is a potent sympatholytic drug with central neural effects. The aim of this study was to evaluate the effects of clonidine on arterial baroreflex sensitivity (BRS) and cardiopulmonary (CP) baroreflex control of muscle sympathetic nerve activity (MSNA) in patients with left ventricular (LV) dysfunction.

Method:   Twenty patients were randomly assigned to either clonidine or placebo groups (10 in each group). BRS (by phenylephrine method) and CP baroreflex (by lower body negative pressure) effects on sympathetic nerve activity (circulating norepinephrine and MSNA recordings) were measured before and after a 4-week treatment period.

Results:   Clonidine lowered blood pressure and heart rate. Clonidine was accompanied not only by a decrease in plasma noradrenaline (from 444±196 to 260±144 pg ml(-1) ) but also by a reduction in directly measured MSNA (from 47±16 to 36±16 bursts min(-1) ). BRS increased significantly from 3·01±1·19 to 6·86±2·84 ms mmHg(-1) after clonidine. When expressed as per cent change in MSNA during CP baroreceptor stimulation, CP baroreflex control of MSNA was significantly increased from 9·26±8·93% to 28·83±11·96% after clonidine. However, there were no significant changes in the measured variables in the control group.

Conclusion:   Clonidine enhanced BRS and CP baroreflex control of MSNA while reducing baseline sympathetic activity in patients with LV dysfunction.