Closed-loop identification of carotid sinus baroreflex transfer characteristics using electrical stimulation

Abstract

Although random aortic pressure (AOP) perturbation according to a binary white noise sequence enables us to estimate open-loop dynamic characteristics of the carotid sinus baroreflex under closed-loop conditions, the necessity of arterial catheter implantation limits the applicability of this method in freely moving animal experiments. Thus, we explored a closed-loop system identification method using electrical stimulation. In 6 anesthetized and vagotomized rabbits, we stimulated the aortic depressor nerve with a binary white noise sequence (0-10Hz) under baroreflex closed-loop conditions while measuring cardiac sympathetic nerve activity (SNA) and AOP. We used a closed-loop identification method to estimate the peripheral arc transfer function from SNA to AOP. The peripheral arc transfer function approximated a second-order low-pass filter and its fitted parameters did not differ from those obtained by an open-loop identification method (dynamic gain: 1.16±0.32 vs. 1.02±0.11; natural frequency: 0.08±0.03 vs. 0.09±0.03Hz; damping ratio: 1.53±0.15 vs. 1.57±0.21). In 6 different rabbits, we applied intermittent rapid pacing (396 beats/min) under baroreflex closed-loop conditions to estimate the neural arc transfer function from AOP to SNA. The neural arc transfer function approximated a first-order high-pass filter and its fitted parameters did not differ from those obtained by an open-loop identification method (dynamic gain: -1.15±0.45 vs. -1.06±0.05; corner frequency: 0.12±0.05 vs. 0.13±0.03 Hz). In conclusion, the closed-loop identification method using electrical stimulation is effective to estimate the neural and peripheral arc transfer functions.