Estimation of Baroreflex Gain Using a Baroreflex Equilibrium Diagram.

Two types of closed-loop perturbations can be applied to the arterial baroreflex system. The first (P(D1)) is introduced into the baroreceptors without a direct effect on arterial pressure (AP), whereas the second (P(D2)) initially affects AP. Neck suction and hemorrhage are examples of P(D1) and P(D2), respectively. To estimate the baroreflex open-loop gain (G(Baro)) without knowing the absolute magnitudes of P(D1) and P(D2), we explored a new strategy to estimate G(Baro) by combining P(D1) and P(D2) in a baroreflex equilibrium diagram. In this diagram, the neural arc presents the input-output relationship between baroreceptor pressure input and sympathetic nerve activity (SNA). The peripheral arc presents the input-output relationship between SNA and AP. In 8 anesthetized rabbits, we estimated G(Baro) by multiplying the slopes of the peripheral arc determined from P(D1) and the neural arc determined from P(D2). We also estimated G(Baro) by a conventional open-loop analysis. The G(Baro) values estimated by the equilibrium diagram and the open-loop analysis showed a positive correlation (y = 0.80x + 0.22, r(2) = 0.95) and a standard error of estimate of 0.21 across the animals. We conclude that G(Baro) was estimated well by combining P(D1) and P(D2) in the equilibrium diagram.