Abstract
The arterial baroreflex system plays a key role in maintaining the homeostasis of arterial pressure (AP). Changes in AP affect autonomic nervous activities through the baroreflex neural arc, whereas changes in the autonomic nervous activities, in turn, alter AP through the baroreflex peripheral arc. This closed-loop negative feedback operation makes it difficult to identify open-loop dynamic characteristics of the neural and peripheral arcs. Regarding sympathetic AP controls, we examined the applicability of a nonparametric frequency-domain closed-loop identification method to the carotid sinus baroreflex system in anesthetized rabbits. This article compares the results of an open-loop analysis applied to open-loop data, an open-loop analysis erroneously applied to closed-loop data, and a closed-loop analysis applied to closed-loop data. To facilitate the understanding of the analytical method, sample data files and sample analytical codes were provided. In the closed-loop identification, properties of the unknown central noise that modulated the sympathetic nerve activity and the unknown peripheral noise that fluctuated AP affected the accuracy of the estimation results. A priori knowledge about the open-loop dynamic characteristics of the arterial baroreflex system may be used to advance the assessment of baroreflex function under closed-loop conditions in the future.
Highlights
The arterial baroreflex system is one of the most important negative feedback systems that stabilize arterial pressure (AP)
We compared the results of a closed-loop identification with the open-loop dynamic characteristics of the baroreflex system
The frequency-domain closed-loop identification employing an exogenous pressure perturbation was successful in separately assessing the transfer functions of the neural and peripheral arcs, there remains an issue of estimation accuracy in the higher frequency range of the neural arc and in the lower frequency range of the peripheral arc
Summary
The arterial baroreflex system is one of the most important negative feedback systems that stabilize arterial pressure (AP). The dynamic gain of the peripheral arc transfer function decreased as the frequency increased from 0.05 to 1 Hz, indicating the low-pass characteristics of the cardiovascular response to SNA (Figure 4A). In the user-defined function simplex, the fitting weight of the error between the model and estimated transfer functions is reduced by a factor of 1/k according to Eq 3.5.3 because the data points become denser as the frequency increased on the Bode plot. The open-loop dynamic characteristics of the total reflex arc can be directly estimated as a transfer function from CSP to AP using the following codes:. In these plots, the SNA values were normalized by the averaged dynamic gain value of the neural arc below 0.03 Hz and expressed in arbitrary units (au). The parameter fc was not compared because the lack of input power in the higher frequency range hampered a reliable estimation of fc in the closed-loop method
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