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

A transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows high-pass characteristics in the frequency range from 0.01 to 1 Hz in anesthetized rabbits. The high-pass characteristics of the neural arc contribute to a quick and stable arterial pressure (AP) regulation. However, if the high-pass characteristics hold up to the frequency of heart rate (3-5 Hz), a pulsatile pressure component in AP would yield an extremely large amplitude of pulsatility in SNA. Such a large amplitude in SNA would hit the nonlinearities in baroreflex pathways, thereby disable the baroreflex regulation of AP. We hypothesized therefore that the transfer gain at the frequency of heart rate would-be much smaller than that predicted from the high-pass characteristics of the neural arc. In anesthetized rabbits (n=6), we perturbed carotid sinus pressure (CSP) according to a binary white noise with a switching interval of 50 ms. The transfer function from CSP to cardiac SNA was then estimated in the range from 0.012 to 10 Hz. The neural arc transfer function showed high-pass characteristics in the frequencies below 0.7 Hz, while losing the transfer gain above the frequency at -20 dB/decade. A simulation study indicated that the attenuation of the pulsatile pressure component in the neural arc was effective to retain the reflex regulation of AP.