Estimation of Total Baroreflex Gain Using an Equilibrium Diagram between Sympathetic Nerve Activity and Arterial Pressure

The arterial baroreflex system may be divided into the mechano-neural arc from pressure input to sympathetic nerve activity (SNA) and the neuro-mechanical arc from SNA to arterial pressure (AP). We explored a new strategy to estimate total baroreflex gain (Gbaro) using an equilibrium diagram between the mechano-neural and neuromechanical arcs. In 8 anesthetized rabbits, a neck suction procedure (NS) was simulated by shifting isolated carotid sinus pressure above AP by 30 mmHg. NS shifted the mechano-neural arc alone, yielding the slope of the neuromehcnaical arc around the operating point. A lower body negative pressure procedure (LBNP) was simulated by 5ml/kg hemorrhage. LBNP shifted the neuro-mechanical arc alone, yielding the slope of the mechano-neural arc around the operating point. By multiplying the slopes of the neuromechanical and mechano-neural arcs, we obtained Gbaro under baroreflex closed-loop conditions. We also estimated Gbaro from the relationship between isolated carotid sinus pressure and AP under baroreflex open-loop conditions. Gbaro estimated by the equilibrium diagram matched reasonably well with that estimated by the open-loop method (y=1.06x−0.09, r=0.96, SEE=0.15). In conclusion, Gbaro could be estimated using the equilibrium diagram without opening the baroreflex negative feedback loop when data obtained from NS and LBNP were combined in a given subject. Keywordsopen-loop analysis, closed-loop analysis