Figure 3. Open-loop transfer function.

A, typical representative data of one rabbit in protocol 2, showing time series of carotid sinus pressure (CSP), sympathetic nerve activity (SNA) and systemic arterial pressure (AP) during CSP perturbation in open-loop baroreflex condition. CSP is changed according to a binary random (white-noise) signal with a switching interval of 500 ms. B, input power spectrum of CSP (green line) is reasonably flat up to 1 Hz. Autospectra of SNA (top line) and systemic AP (bottom line) are also shown. The arrowhead indicates a peak of SNA autospectrum at 0.4 Hz. C, open-loop transfer functions of the neural arc (H_n-open) from CSP input to SNA (left panels) and of the peripheral arc (H_p-open) from SNA input to AP (right panels) identified in the same animal as in A. The gain (top), phase (second), coherence (third) and normalized random error (Error, bottom) functions are shown. Units of gain are [a.u. mmHg⁻¹] for the neural arc and [mmHg a.u.⁻¹] for the peripheral arc, respectively. D, step responses (Step res.) derived from the transfer functions shown in C. The units are [a.u.] for the neural arc and [mmHg] for the peripheral arc, respectively. E, open-loop transfer functions of the total arc (H_total-open) from CSP input to AP identified in the same animal as in A. The gain (top), phase (second), coherence (third) and normalized random error (Error, bottom) functions are shown. Unit of gain is [mmHg mmHg⁻¹]. F, step response (Step res.) derived from the transfer function shown in E. The unit is [mmHg]. a.u., arbitrary unit.