Neural regulation of sympathetic nerve activity in heart failure

One of the hallmarks of chronic congestive heart failure is an increase in sympathetic tone to the peripheral circulation and to the heart. A correlation between plasma norepinephrine and the severity of the heart failure state has been demonstrated. One mechanism that has been proposed to account for this sympathoexcitation is a depression in the baroreflex and, perhaps, cardiac reflex control of sympathetic nerve activity. This review summarizes work from several laboratories, including our own, that documents a depressed baroreflex control of heart rate and sympathetic nerve activity in both animals and humans with heart failure. The mechanism of the depressed baroreflex most likely is caused by reduced baroreceptor sensitivity as well as enhanced input to the central nervous system from cardiac receptors that are chemosensitive. Although sympathetic tone and arterial baroreflex sensitivity are altered in heart failure, there have been no studies showing a cause-and-effect relationship. Increases in plasma norepinephrine are similar in baroreceptor-denervated and intact dogs paced into heart failure. This latter observation cells into question the traditional concept of baroreceptor-mediated increases in sympathetic tone in heart failure.