Carotid sinus baroreceptor reflex in dogs with experimental heart failure

We have previously demonstrated a decrease in baroreceptor discharge sensitivity in dogs with experimental heart failure. In the present study, we determined the sensitivity of the carotid sinus baroreceptor reflex in dogs with pacing-induced heart failure. The carotid sinus baroreceptor reflex sensitivity was determined by pressurizing one carotid sinus with all other baroreceptor and cardiopulmonary receptor inputs removed. The data were analyzed by plotting carotid sinus pressure-mean arterial pressure curves and carotid sinus pressure-renal sympathetic nerve activity curves in the two groups of dogs. The peak arterial pressure during carotid hypotension was significantly depressed in dogs with heart failure compared with normal dogs (107.1 ± 5.7 versus 139.8 ± 7.0 mm Hg, p < 0.001). Mean arterial pressure range, renal sympathetic nerve activity range, and peak slope were significantly decreased in the heart-failure group. To determine if this depression was completely due to depression of baroreceptor discharge per se, or to alterations in central or end-organ responsiveness, similar experiments were performed by stimulating the carotid sinus nerve and evaluating frequency, voltage, and duration of stimulation on the resultant mean arterial pressure and renal sympathetic nerve activity. As was the case with carotid sinus pressurization, electrical stimulation caused a significantly smaller change in mean arterial pressure in heart-failure dogs compared with the normal dogs. However, there was no significant difference between normal and heart-failure dogs for the renal sympathetic nerve activity-electrical stimulation curves. These data strongly suggest that the depressed carotid sinus baroreceptor reflex in heart failure is not solely the result of depressed baroreceptor responsiveness but may be related to poor end-organ responses and normal central control of renal sympathetic outflow.