Estimation of Baroreflex Gain Using a Baroreflex Equilibrium Diagram

Abstract

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, r² = 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.