Baroreflex control of renal sympathetic nerve activity is preserved in heart failure despite reduced arterial baroreceptor sensitivity.

The purpose of this study was to determine if arterial baroreflex control of sympathetic nerve traffic is impaired in heart failure. We recorded renal nerve activity during changes in arterial pressure while simultaneously recording from aortic baroreceptor afferent fibers in 10 dogs with heart failure induced by rapid ventricular pacing and in 10 sham animals. Sensitivity of the aortic baroreceptors (percent change in nerve activity per millimeters mercury change in mean arterial pressure) was reduced in the heart failure group (heart failure, 2.3 +/- 0.3; sham, 3.6 +/- 0.4, p = 0.02). Despite the reduced sensitivity of aortic baroreceptors in heart failure, there was no difference in the baroreflex gain of renal nerve activity (heart failure, -5.5 +/- 1.4; sham, -5.8 +/- 1.3, p = NS). These values tended to decrease in both groups after vagotomy. The relation between baroreceptor input and renal sympathetic output, or central baroreflex gain (percent change in renal nerve activity divided by percent change in aortic nerve activity) was similar in both groups before vagotomy (heart failure, -2.4 +/- 0.6; sham, -2.3 +/- 0.5, p = NS). Vagotomy reduced central gain in the sham group (-0.9 +/- 0.1, p = 0.03) but not in the heart failure group (-1.7 +/- 0.5, p = NS), suggesting that the contribution of vagal afferents in the baroreflex arc is reduced in heart failure. Baroreflex control of R-R interval was attenuated in heart failure when assessed by blood pressure elevation but not reduction, indicating abnormal parasympathetic but preserved cardiac sympathetic mechanisms in heart failure. Thus, dogs with heart failure exhibit reduced sensitivity of aortic baroreceptors but preserved baroreflex control of renal nerve activity. Reduced baroreceptor sensitivity with preservation of baroreflex control of sympathetic nerve activity may contribute to the sympathoexcitatory state known to exist in heart failure.