DIFFERENTIAL EFFECT OF ACUTE BARORECEPTOR UNLOADING ON CARDIAC AND SYSTEMIC SYMPATHETIC TONE IN CONGESTIVE-HEART-FAILURE

Objectives. The present study was designed to identify the hemodynamic factor or factors that reflexly contribute to activation of the cardi ac sympathetic nerves in patients,vith severe congestive heart failure (CHF). Background. We and others have previously shown that activatio n of the sympathetic nervous system is a key feature of CHF in humans. Furthermore, the degree of sympathetic activation shows marked region al heterogeneity and is most pronounced in the heart. Recent studies h ave shown a significant positive relation between pulmonary artery pre ssure and the magnitude of cardiac sympathetic activation. Of particul ar importance, the degree of cardiac sympathoexcitation has also been shown to be strongly associated with mortality in CHF. Methods. We ass essed total systemic and cardiac sympathetic activity (norepinephrine [NE] spillover method) in nine patients with severe CHF and significan tly elevated pulmonary artery pressure (mean [+/-SEM] pulmonary artery pressure 46 +/- 3 mm Hg) at rest and during a titrated infusion of so dium nitroprusside (SNP). Results. SNP infusion significantly reduced mean arterial blood pressure, pulmonary artery pressure and pulmonary capillary wedge pressure. During SNP infusion, the total body NE spill over rate (NESR) increased (from 7.9 +/- 1.7 to 11.2 +/- 3.1 nmol/min, p < 0.01), whereas the cardiac NESR decreased (from 522 +/- 86 to 409 +/- 71 pmol/min, p < 0.05). The ratio of cardiac/total NE spillover w as also substantially reduced (from 7.8 +/- 1.3 to 4.9 +/- 0.9%, p < 0 .001). Conclusions. There is a directionally opposite change in whole- body (increase) and cardiac (reduction) sympathetic nervous activity d uring SNP infusion, most likely due to unloading of arterial barorecep tors and specific cardiopulmonary baroreceptors, respectively, in seve re CHF. These observations support the concept of a positive feedback relation between pulmonary artery pressure/filling pressure and cardia c sympathetic tone in CHF and serve to reinforce the importance of vas odilator therapy in this condition. (C) 1998 by the American College o f Cardiology.