Figure 11. A numerical simulation of the effects of noise on calculation of baroreflex transfer functions.

Noise (Gaussian white-noise) is introduced to the neural and/or peripheral arcs in closed-loop-spontaneous baroreflex condition, where CSP equals AP (see Figure 1C). A, the original baroreflex transfer functions of the neural (H_n, left panel) and peripheral (H_p, right panel) arcs. H_n is modelled using derivative and high-cut filter characteristics with a pure delay, and H_p using the second-order low-pass filter with a pure delay (see Appendix B). Units of gain are a.u. mmHg⁻¹ for H_n and mmHg a.u.⁻¹ for H_p, respectively. B–D, block diagrams (upper panels) and closed-loop-spontaneous transfer functions (lower panels); calculated from AP to SNA as the neural arc (left lower panel) and from SNA to AP as the peripheral arc (right lower panel). The open-loop transfer functions (H_n, H_p) are included as reference (gray lines). Units of gain are a.u. mmHg⁻¹ for the neural arc and mmHg a.u.⁻¹ for the peripheral arc, respectively. B, first simulation: noise (0.029, 0.117, 0.264, 0.732 and 2.928 × 10³ au²) is present only in the neural arc. The same results are obtained irrespective of the noise intensity. The closed-loop-spontaneous transfer function of the neural arc is totally different from the open-loop transfer function H_n, whereas that of the peripheral arc overlaps with H_p. C: Second simulation: noise (0.029, 0.117, 0.264, 0.732 and 2.928 × 10³ mmHg² is present only in the peripheral arc. The same results are obtained irrespective of the noise intensity. The closed-loop-spontaneous transfer function of the neural arc overlaps the open-loop transfer function H_n, whereas that of the peripheral arc is markedly different from H_n. D, third simulation: noise with incremental intensity [from 0.029 (broken line) to 0.117, 0.264, 0.732 and 2.928 (solid lines) × 10³ au²] is present in the neural arc, while a small constant noise (29 mmHg²) is present in the peripheral arc. The closed-loop-spontaneous transfer function of the neural arc is different from the open-loop transfer function of H_n, whereas that of the peripheral arc approaches H_p and the two become overlapped as the noise in the neural arc increases. H_n, neural arc transfer function; H_p, peripheral arc transfer function, NN, unknown neural noise; PN, unknown peripheral noise.