Dynamic arterial baroreflex in rabbits with heart failure induced by rapid pacing.

Excessive sympathetic nerve activity in heart failure could be attributable to impaired arterial baroreflex function. Employing transfer function analysis, we evaluated the arterial baroreflex in control rabbits (n = 8) and in rabbits with rapid pacing-induced heart failure (n = 10) in a dynamic manner. Rabbits in the heart-failure group showed elevated filling pressures, depressed first derivative of left ventricular pressure, pulmonary congestion, and an increased level of plasma norepinephrine. Varying aortic pressure pseudorandomly and recording responses in renal nerve activity, we calculated the transfer function from aortic pressure to renal nerve activity. The gain of the transfer function was similar between control and heart-failure rabbits over 0.04-0.4 Hz as well as the phase and the coherence, indicating that the dynamic arterial baroreflex was preserved in our rabbit heart-failure model. Vagotomy increased the gain of the arterial baroreflex over 0.04-0.4 Hz in control (P < 0.05) but not in heart-failure rabbits, indicating that vagal afferents, which normally inhibit the dynamic arterial baroreflex, no more did so in heart failure. We conclude that excessive sympathetic nerve activity in heart failure may not be due to impaired dynamic arterial baroreflex, but that this apparently preserved arterial baroreflex in heart failure may be due to impaired cardiopulmonary baroreflex.