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 (G/sub baro/) using an equilibrium diagram between the mechano-neural and neuro-mechanical 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 neuro-mechanical arc around the operating point. A lower body negative pressure procedure (LBNP) was simulated by 5 ml/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 neuro-mechanical and mechano-neural arcs, we obtained G/sub baro/ under baroreflex closed-loop conditions. We also estimated G/sub baro/ from the relationship between isolated carotid sinus pressure and AP under baroreflex open-loop conditions. G.. estimated by the equilibrium diagram matched reasonably well with that estimated by the open-loop method (y=1.06/spl times/-0.09, r/sup 2/=0.96, SEE=0.15). In conclusion, G/sub baro/ 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.