Neural loop of baroreflex optimizes dynamic arterial pressure regulation

The baroreflex loop consists of both a fast neural arc and a slow mechanical arc. We hypothesized that the neural arc of the baroreflex compensates the slow mechanical response and thereby substantially improves the quality of blood pressure regulation. In 12 anesthetized, vagotomized rabbits, we isolated carotid sinuses and randomly changed intrasinus pressure while measuring intrasinus pressure (P_s), cardiac sympathetic nerve activity (SNA) and systemic arterial pressure (P_a) using a white noise technique. We estimated the open-loop transfer characteristics of the neural arc (Hn) of the baroreflex, that is, from P_s to SNA, that of the peripheral mechanical arc (Hp), from SNA to P_a, and that of the total baroreflex loop (Ht). The gain of Hn was constant below 0.12±0.057 Hz and increased with a slope of about 6 dB/octave above it, suggesting that the response was increasingly faster with frequency. In contrast, the gain of Hp was constant below 0.071±0.030 Hz and decreased with a slope of about -12dB/octave above it, suggesting the response progressively slowed with increasing frequency. 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