Neural arc of baroreflex optimizes dynamic pressure regulation in achieving both stability and quickness

Abstract

The baroreflex loop consists of a fast neural arc and a slow mechanical arc. We hypothesized that the neural baroreflex arc compensates the slow mechanical response and thus improves the quality of blood pressure regulation. We estimated the open-loop transfer characteristics of the neural baroreflex arc (HP), i.e., from carotid sinus pressure to sympathetic nerve activity (SNA), and that of the effective peripheral baroreflex arc (Hp), i.e., from SNA to arterial pressure, in anesthetized rabbits. The gain of Hn was constant below 0.12 +/- 0.057 Hz and increased with a slope of 6.1 +/- 0.06 dB/octave above its frequency up to 1 Hz. In contrast, the gain of Hp was constant below 0.071 +/- 0.03 Hz and decreased with a slope of -11.0 +/- 1.48 dB/octave above the frequency. These data indicate that Hn accelerates slow peripheral responses in the frequency range of 0.1-1 Hz. Although too much acceleration in the high-frequency range could result in instability of the system, numerical analysis of the closed-loop baroreflex response indicated that the neural arc optimized arterial pressure regulation in achieving both stability and quickness.

Attenuation of a pulsatile pressure component in the neural arc of the arterial baroreflex

“…Although the high-pass characteristics of the neural arc have been identified in our previous study [1], the transfer function of the neural arc around the frequency of heart rate (3-5H in rabbits) remained unknown. To our best knowledge, this is the first to reveal the neural arc transfer function beyond 1 Hz (Figure 1).…”

“…We set ƒ C1 and ƒ C2 at 0.1 and 0.8 Hz, respectively. For both SIM1 and SIM2, the peripheral arc transfer function was modeled using a second-order low-pass filter with a lag time as follows [1]. First, we simulated the closed-loop AP response against 40-mmHg stepwise pressure decrease using SIM1 and SIM2 without including any nonlinearities.…”

“…A numerical simulation indicated that the fast neural arc compensated for the slow peripheral arc to achieve a quick and stable AP regulation. This simulation result was obtained based on nonpulsatile AP [1]. However, if we made AP pulsatile (4-Hz sinusoid with peak-to-peak amplitude of 20 mmHg), the pulsatile pressure yield an extremely large amplitude of pusatility in SNA due to the high-pass characteristics of the neural arc.…”

“…Estimation of transfer functions among cardiovascular variables is useful in providing insight into the mechanisms of cardiovascular regulation [1][2][3][4][5][6]. In a previous study, we decomposed the carotid sinus baroreflex system into the neural arc from carotid sinus pressure (CSP) to sympathetic nerve activity (SNA) and the peripheral arc from SNA to arterial pressure (AP) [1].…”

“…In a previous study, we decomposed the carotid sinus baroreflex system into the neural arc from carotid sinus pressure (CSP) to sympathetic nerve activity (SNA) and the peripheral arc from SNA to arterial pressure (AP) [1]. A transfer function analysis revealed that the neural arc approximates the first-order high-pass filter in the frequency range between 0.01 and 1 Hz.…”